A PROMISE OF SPACE
by
ARTHUR C. CLARKE


Nonfiction

BY THE SAME AUTHOR

NONFICTION FICTION

Interplanetary Flight Islands in the Sky

The Exploration of Space Prelude to Space

Going Into Space Against the Fall of Night

The Coast of Coral The Sands of Mars

The Making of a Moon Childhood's End

The Reefs of Taprobane Expedition to Earth

Voice Across the Sea Earthlight

The Challenge of the Reach for Tomorrow

Spaceship The City and the Stars

Profiles of the Future Talcs from the "White Hart"

Voices from the Sky The Deep Range

The Other Side of the Sky with R. A. Smith: A Fall of Moondust

The Exploration of the Moon From the Ocean, From the

Stars with Mike Wilson: Tales of Ten Worlds

The First Five Fathoms Dolphin Island

Boy Beneath the Sea Glidepath

Indian Ocean Adventure Across the Sea of Stars

The Treasure of the Great Prelude to Mars

Reef

Indian Ocean Treasure with Stanley Kubrick:

2001: A Space Odyssey with the Editors of Life: (novel and
screenplay)

Man and Space

THE PROMISE OF SPACE

Arthur Clarke

PYRAMID BOOKS

At NEW YORK

THE PROMISE OF SPACE

A PYRAMID BOOK

Published by arrangement with Harper & Row, Publishers

Harper & Row edition published June 1968

Pyramid edition published February 1970

Copyright @ 1968 by Arthur C. Clarke

Library of Congress Catalog Card Number: 68-17042

All rights reserved.  No part of this book may be used or reproduced in
any manner whatsoever without written permission except in the case of
brief quotations embodied in critical articles and reviews.

Printed in the United States of America

PYRAMID BOOKS are published by Pyramid Publications A Division of The

Walter Reade Organization, Inc.  444 Madison Avenue, New York, New
York

10022, U.S.A.

CONTENTS

ACKNOWLEDGMENTS 9

INTRODUCTION 10

1. BEGINNINGS

1. IMAGINARY VOYAGES 19

2. FROM FANTASY TO SCIENCE 30

3. "NOTHING TO PUSH AGAINST" 41

4. POWER FOR SPACE 47

5. ESCAPE FROM EARTH 60

6. OTHER ORBITS, OTHER MOONS 70

7. THE PRICE OF SPEED 76

Il.  AROUND THE EARTH

8. MOONRISE IN THE WEST 89

9. OPENING SKIES 103

10.  FIRST HARVEST 112

11.  MAN IN OR 131T 133

12.  ISLAND IN THE SKY 148

HL AROUND THE MOON

13.  VOYAGERS TO THE MOON 161

14.  THE BIRTH OF APOLLO 181

15.  THE VEHICLE 187

16.  THE MISSION 197

17.  THE MOON 214

18.  THE USES OF THE MOON 221

19.  THE LUNAR COLONY 233

IV.  AROUND THE SUN

20.  THE TRILLION-MILE WHIRLPOOL 241

21.  PATHS TO THE PLANETS 248

22.  CHILDREN OF THE SUN 260

23.  THE OUTER GIANTS 273

24.  THE COMMERCE OF THE HEAVENS 281

25.  TOMORROW'S WORLDS 292

V. AROUND THE UNIVERSE

26.  OTHER SUNS THAN OURS 305

27.  ACROSS THE ABYSS 319

28.  TO THE STARS 326

29.  WHERE'S EVERYBODY?  338

30.  CONCERNING MEANS AND ENDS 347

BIBLIOGRAPHY 355

INDEX 357

ILLUSTRATIONS

FIGURES

1. The rocket principle.43

2. The forces in the rocket engine.  45

3. Solid-propellant rockets.  49

4. Liquid-propellant rocket.  51

5. Gravity and distance.  64

6. The gravitational fields of Earth and Moon.  68

7. Orbits in the Earth's gravitational crater.  71

8. Orbits, around the Earth.  74

9. The rocket-velocity law.  79

10.  Rocket mass ratios.  81

11.  Weight breakdowns of one- and two-stage rockets.  82

12.  Angular speeds of satellites.  97

13.  Ground track of low-inclination orbit.  99

14.  Applications satellites.  101

15.  The transparency of the atmosphere at varying wave lengths.  109

16.  The Apollo mission.  213

17.  Libration points in the Earth-Moon system.  232

18.  The Solar System.  243

19.  The gravitational field of the Sun.  246

20.  Hohmann orbits to Mars and Venus.  249

21.  High-speed orbits around the Sun.  253

22.  Orbit of Mariner 4. 256

23.  Mars fly-by mission.  257

24.  Orbit of Jupiter probe.  259

25.  SoUd-core nuclear rocket.  284

PLATES

1. Automatic rocket surveying Mars.  13

2. Lunar-type spaceship.  15

3. Tsiolkovsky Crater.  33

4. Goddard and one of his rockets.  35

5. V-2 being prepared for launching.  54

6. Titan 3. 58

7. Sputnik-carrying rocket.  92-93

8. The Pageos satellite.  105

9. Unmanned orbital telescope.  III

10.  Map-photo from pictures taken by

ESSA satellite.  114-115

11.  Engineer with antennae of ATS I satellite.  118

12.  ATS communications satellite.  119

13.  Cloud patterns photographed by ATS 1. 122

14.  Tycho Crater, photographed by Lunar Orbiter 5. 124

15.  Photograph of Gemini 7 taken by Gemini 6. 125

16.  Telstar communications satellite.  127

17.  Syncom communications satellite.  128

18.  Syncom satellite without covering.  129

19.  Final checkout of Early Bird satellite.  130

20.  InteWat communications satellite.  132

21.  Vostok I before flight.  135

22.  Vostok 1. 138

23.  Vostok 1 after atmospheric re-entry.  139

24.  Space station.  151

25.  Adjusting the antenna of Ranger 2. 166

26.  Surveyor 3 model.  167

27.  Surveyor I's photo of a lunar boulder.  172

28.  Surveyor satellite.  173

29.  Antenna used to track Surveyor 1. 174

30.  Model of Lunar Orbiter.  175

31.  The Earth, seen from the Moon by Orbiter 1. 176

32.  Earth photographed by Lunar Orbiter 5. 177

33.  Orbiter 2s close-up of Copernicus Crater.  178-179

APOLLO MISSION

34.  Saturn 5 space vehicle used in Apollo missions.  190

35.  Sectional view of Saturn 5. 191

36.  Saturn S-II stage.  192

37.  Saturn S-IVB stage.  192

38.  Command Module subsystems.  193

39.  Service Module subsystems.  193

40.  Model of Lunar Module.  194

41.  Jettisoning of first stage (SIC ). 200

42.  Jettisoning of second stage (S-II).  200

43.  Command and Service Modules.  204

44.  Command and Service Modules.  205

45.  Command and Service Modules.  204

46.  Jettisoning of S-IVB stage after docking.  205

47.  Command and Service Modules.  206

48.  Lunar Module separates from Comm-and and

Service Modules.  206

49.  Astronaut Aldrin descends to the surface of the Moon.  207

50.  Astronaut Aldrin on the Moon.  208

50A.  Apollo 1 I's Lunar Module on the Moon.  209

51.  Moon as seen from Earth.  215

52.  The Mare Orientale.  218

53.  Surveyor 1 photograph of the Moon's surface.  224

54.  The Hyginus Rille.  226

55.  A 17-meter rolling rock in Vitello Crater.  227

56.  A lunar canyon discovered by Lunar Orbiter 4. 228

57.  One of the first photos of the Moon'ssurface.  236

58.  Mars, Jupiter, Saturn, and Pluto.  261

59.  Mariner spacecraft and launch-vehicle system.  270

60.  Mariner 4's photograph Number 11 of Mars.  272

61.  The Martian terrain.  308-309

62.  Star clouds in the Milky Way, Sagittarius region.  311

63.  A globular star cluster.  315

64.  Spiral nebula in Ursa Major.  317

ACKNOWLEDGMENTS

It would be quite impossible to thank all those who have helped me,
directly or indirectly, during the preparation of this book, but I
would like to express my particular gratitude to the following:

Mrs.  Esther C. Goddard James Webb, NASA Administrator; George Mueller,
Associate Administrator for

Manned Space Flight; Julian Scheer, Director of Public Affairs; Dr.
Eugene

M. Emme, NASA Historian; Captain Robert Freitag; Jay Holmes Dr. Wernher
von Braun, Director, Marshall Space Flight Center, Huntsville Dr. 
Joseph Charyk, President, Communications Satellite Corporation Dr.
Edward Welsh, Executive Secretary, National Aeronautics and Space
Council Frederick C. Durant III, Assistant Director (Astronautics),
Smithsonian

Institution/ National Air and Space Museum

Ellis Levin' Systems Manager, Lunar Orbiter, Boeing Dr.  Harold Rosen,
Philip Rubin, Hughes Aircraft Company, Space Systems Division A. V.
Cleaver, O.B.E."  Chief Engineer and Manager, Rocket Department,

Rolls-Royce, Ltd.  Michael Watson, Manager, International Programs,
Advanced Programs Development,

Space Division, North American Rockwell Corporation And especially Bob
and Barbara Silverberg, for their work in checking, collecting
illustrations, proofreading, and generally coping with the sordid
details.

INTRODUCTION

A generation has now arisen that can hardly remember and can scarcely
credit-the days when anyone who talked seriously about space travel was
likely to have his sanity questioned.  That particular battle has been
won, but another, equally important, is still in progress.  Although
there can be no informed person today who doubts the technical
feasibility of manned flight to the Moon and planets, there are many
who question its value and argue that everything we need to learn about
the Solar System can be gathered by robot probes.  Others, while
agreeing that lunar and interplanetary expeditions will be of great
scientific value, think that our current drive into space has been too
much motivated by politics to be altogether healthy and believe that it
should proceed with more caution, care, and-above all-economy.
Professor J. D. Bernal once remarked that wars are run, not by logic,
but by "gusts of emotion."  There are many who would apply this phrase
to the United States space program, at least in its earlier days.

Some of this criticism is valid; some is itself based on
emotion-understandably so, in the case of scientists who may see
billions going into space when they cannot get thousands for their own
pet projects.

However, much is based on a total failure to grasp the long-term
implications of space flight.  After all the lessons that the history
of our age has given us, this failure is inexcusable; and to those who
continue to make it, it may be disastrous.

Astronautical enthusiasts are fond of quoting Senator Daniel Webster
(1782-1852), who once refused to vote a single cent to the opening up
of the West-as it would always be a howling wilderness, of no use to
anyone except savages.  (Los Angelophobes may consider that he had a
point.) tTnfortunately, there are still plenty of Daniel Websters
around, and before time disposes of their objections, they can do much
harm.  Dr.

Frederick Seitz, president of the National Academy of Science, put the
matter very well when He said that our children will wonder what manner
of people we were, that we ever questioned the value of space
exploration.

Every revolutionary idea-in science, politics, art or whatever-seems to
evoke three stages of reaction.  They may be summed up by the phrases:
(1)

"It's completely impossible-don't waste my time"; (2) "It's possible,
but it's not worth doing"; (3) "I said it was a good idea all along."
At the moment, astronautics is still passing through stage 2; I hope
that this book will smooth the transition into stage 3.

It is now thirty years since my earliest articles on space flight
appeared, and twenty since I began work on my first book,
Interplanetary Flight (1950).  Though intended for a technical series,
its sales encouraged my editor, Jim Reynolds, to talk me into writing a
more popular book for a wider audience.  This was The ExplOration of
Space (1951); as was stated in its preface it was aimed at "all those
who are interested in the 'why' and 'how' of astronautics, yet do not
wish to go into too many scientific details.  I believe that there is
nothing in this book that the intelligent layman could not follow; he
may encomiter unfamiliar ideas, but that will be owing to the very
nature of the subject, and in this respect He will be no worse off than
many specialists."  This description is also, I hope, true of the
present work.

Few conibinatious of' words are more hostility-provoking than the
tiresome phrase "I told you So," but Perhaps I may be allowed a few
nostalgic flashbacks from The Exploratioti of Spacc.  One of' the
photographs,

"Automatic Rocket Sin-veying Mars," vas described as follows:

The little rocket (the last step of a far larger niachinc) left the
Earth 250 days ago and dining, that time has been coasting freely, like
a comet, along the path that leads to Mars with the least expenditure
of fuel..  . Under the guid

Introduction ance of a tiny yet extremely complex electronic brain, the
missile is now surveying the planet at close quarters.  A camera is
photographing the landscape below, and the resulting pictures are being
transmitted to the distant Earth along a narrow, radio beam.  It is
unlikely that true television would be possible, with an apparatus as
small as this, over such ranges.  The best that could be expected is
that still-pictures could be transmitted at intervals of a few
minutes..  ..

This missile will certainly look peculiar to anyone who imagines that
rockets must be sleek, streamlined projectiles with sharply pointed
noses.

But such refinements are not only unnecessary but actually wasteful on
rockets that are launched in airless space.  This reconnaissance
missile would be carried inside a much larger rocket on its way tip
through the

Earth's atmosphere, its outrigger arms possibly folded together during
this stage, and extended when it had entered space.  [Plate 1]

With the sut)stitution of "hours" for "minutes," this is almost a
precise description of Mariner 4, launched thirteen years later.  As
the plates show, the vehicles themselves have a striking family
resemblance-though it is not likely that Plate I ever had the slightest
influence on the jet

Propulsion Laboratory designers.  A given problem must evoke the same
kind of solution from any group of engineers, as from Nature herself;
witness the superficially identical sharks, dolphins, and
ichtliyosaurs.

The layout of this Proto-Mariner was evolved by one of the most active
members of the British Interplanetary Society, the late R. A. Smith.
Ralph

Smith's unusual combination of artistic and technical skills did much
to popularize astronautics in the 1940's and 1950's; he was responsible
for the main illustrations in The Exploration of Space.  Particularly
impressive now, when compared with the Apollo Lunar Module, is his

Lunar-type Spaceship (Plate 2), which is still of considerable historic
interest.  Based on a design study which first appeared in the January,
1939, issue of the Journal of the Britivh Interplanetary Society, it
may well be one of the earliest attempts to solve, on a fairly
realistic basis, the practical problems of landing on an airless
world-and taking off again.

In 1952-53, assisted by his colleague H. E. Ross, R. A. Smith prepared
a remarkable series of forty-five drawings that showed the possible
development of lunar exploration.  Earth satellites, orbital
rendezvous, extravehicular activities, robot probes, soft-landers, the
first Moon bases, and the establishment of self-sufficient lunar
colonies were

Plate 1. Automatic rocket surveying Mars.

Painting by Leslie Carr, based on a drawing by R. A. Smith all
featured.  These illustrations were published in The Exploration of
the

Moon (1954).  Going through this volume again today, I find that
seventeen of the forty-five events depicted have already occurred,
essentially as we described them; plans for the rest are far advanced.
Though this is very satisfactory in one respect, it does demonstrate
the rapid rate of obsolescence of books on astronautics: they are
likely to date even more swiftly than the hardware.

At the end of 1954 I departed for the Great Barrier Reef of Australia
and was roughing it on a remote island when news came of the United
States' earth-satellite program-the unfortunately named but ultimately
successful

Project Vanguard.  This resulted in another book (again prodded out of
me by

Jim Reynolds), The Making of a Moon (1957).  A hasty revision was
required when the first new moon turned out to be made in the Soviet
Union.

Two years later, I edited and collected all my shorter essays on
astronautics, which were published under the title The Challenge of
the

Spaceship (1959).  For completeness I should also mention Going Into
Space (1953), which, as indicated by the title of the British edition
(The

Introduction

Young Traveller in Space), was intended for the teen-age audience.

Although the explosive development of astronautics over the last decade
has made these books very out of date, they have remained stubbornly in
print.

The Exploration of Space was partially revised in 1959, and
Interplanetary

Flight in 1960, but the prolonged and near-fatal flirtation with the
Indian

Ocean reported in The Treasure of the Great Reef (1964) left me neither
time nor energy for the complete rewriting that was really required.

Many events have now combined, or conspired, to focus my main interests
once more upon space travel.  Perhaps foremost was three years' hard
labor with Stanley Kubrick on 2001: A Space Odyssey, which made me
start thinking seriously again about probable developments during the
rest of this century.  Another was a conducted tour of Cape Kennedy,
with NASA

Administrator James Webb as guide; yet another was being present at
Comsat

Headquarters the night Early Bird was launched.  I could also mention
the cumulative impact of seeing the first live television picture from
the

Moon--7meeting Yuri Gagarin and John Clennwatching Echo slide through
the equatorial skies-walking thoughtfully around the sacked and ruined
birthplace of the god Apollo, with Leonid Sedov and Wernher von
Braun.

These and similar experiences produced a slight crisis of conscience.
The result is this book, which I am optimistic enough to hope will not
depreciate technologically by more than a few per cent per annum-and so
should still be largely valid through the 1970's.  It is all entirely
new work and replaces all those mentioned above, though I have not
hesitated to quote extensively from them where appropriate (as in
Chapter 1).

And Dow, having done my duty, perhaps I may be allowed to get back to
the equally important business of science fiction.

ARTHUR C. CLARKE Colombo, Ceylon September, 1967

Plate 2. Lunar-type spaceship: sectional view.

Drawing by R. A. Smith

L BEGINNINGS

IMAGINARY VOYAGES

Come, my friends, "Tis not too late to seek a newer world.  To sail
beyond the sunset, and the baths Of all the western stars.

TENNYSON-Ulysses

The very conception of interplanetary travel -vkas, course, impossible
until it was realized that there wert other planets.  That discovery
was much later than we, with our scientific background, sometimes
imagine.  Although

Mercury, Venus, Mars, Jupiter, and Saturn have been known from the very
earliest times, to the ancients they were simply wandering stars.  (The
word "planet" means, in fact, "wanderer.") As to what those stars might
be, that was a question to which every philosopher gave a different
reply.  The followers of Pythagoras, in the sixth century B.C."  made a
shrewd guess at the truth when they taught that the Earth was one of
the planets.  But this doctrine-so obviously opposed to all the
evidence of common sense-was never generally accepted and, indeed, at
the time there were few arguments which could be brought forward to
support it.  To the ancients, therefore, the idea of interplanetary
travel, in the literal sense, was not merely fantastic: it was
meaningless.

However, although the stars and planets were simply dimensionless
points of light, the Sun and Moon were obviously in a different class.
Anyone could see that the), had appreciable size, and the Moon had
markings on its face that might well be interpreted as continents and
seas.

It was not surprising, therefore, that many of the Greek
philosophers-and not only the Pythagoreans-believed that the Moon
really was a world.  They even made estimates of its size and distance,
some of which were not far from the truth.  Once this had been done, it
was natural to speculate about the Moon's nature and to wonder if it
had inhabitants.  And it was natural-or so, at least, it seems to
us-that men should write stories about traveling to that mysterious and
romantic world.

In actual fact, only one writer of ancient times took advantage of this
now classic theme.  He was Lucian of Samosata, who lived in the second
century

A.D. The hero of Lucian's inaccurately entitled True History was taken
to the Moon in a waterspout that caught up his ship when he was sailing
beyond the Pillars of Hercules-a region where, as was well known in
those days, anything was likely to happen.

In a second book, Lucian's hero went to the Moon quite intentionally,
by making a pair of wings, after the fashion of Icarus, and taking off
from

Mount Olympus.  For in Lucian's time, as for many centuries to come, it
was not realized that there was a fundamental difference between aero-
and astronautics.  In A.D. 160 it seemed natural enough to imagine that
if one could make a workable pair of wings, they could be used to take
one to the

Moon.

After Lucian, the theme of space travel was neglected for almost
fifteen hundred years.  When it was again renewed, it was in a very
different intellectual climate.  The modern era had begun: the Earth
was no longer believed to be the center of the universe.  And, above
all, the telescope had been invented.

It is hard for us to imagine astronomy as it was in the days when all
observations had to be made with the naked eye.  We now take the
telescope for granted, but it is only three and a half centuries since
Galileo pointed his first crude instruments at the stars and learned
secrets withheld from all other men since history began.  No scientist
can ever have gathered so rich a harvest in so short a time.  Within a
few weeks Galileo had seen the mountains and valleys of the Moon,
proving that it was indeed a solid world, and had also discovered that
the planets, unlike the stars, showed visible disks.  He had found that
four tiny points of light revolved around Jupiter as the Moon revolves
around the Earth, and the inference was obvious that Jupiter was a
world with four satellites as against Earth's one, appearing small only
because of its immense distance.

This was the first direct revelation of the true scale of the universe:
astronomers had calculated the distances of the planets before, but now
at last man had an instrument with which he could actually see into the
depths of space.  From this moment the old medieval conception of the
universe, with its picture of concentric crystalline spheres carrying
the planets between heaven and Earth, was doomed.  The frontiers of
space receded to an enormous distance: they are receding from us
still.

It is hardly surprising that the first serious story of a journey to
the

Moon appeared within a generation of Galileo's discoveries.  It is,
however, a little surprising that it was written by the greatest
astronomer of the time, indeed, one of the greatest of all time.
Johannes Kepler was the first man to discover the exact laws governing
the movements of the planets-the same laws which now govern the
movements of spacecraft.  During the latter years of his life Kepler
wrote, but did not publish, his

Somnium.  in this book he transported his hero to the Moon by
supernatural means, a retrograde step, one might think, for a
scientist.  But Kepler lived in an age that still believed in magic,
and indeed his own mother had been charged with witchcraft.  He
undoubtedly employed demonic methods of propulsion because he knew of
no natural forces that could undertake the task.  Kepler, unlike his
predecessor Lucian, knew perfectly well that there was no air between
the Earth and the Moon, although he thought that the

Moon itself might have an atmosphere and inhabitants.  His description
of the Moon was the first one to be based on the new knowledge revealed
by the telescope, and it had a great influence on all future writers
(including H. G. Wells, two and a half centuries later).

Kepler's book was published in 1634.  Only four years afterward the
first

English story of a lunar trip appeared Bishop Godwin's Man in the
Moone.

Godwin's hero, Domingo Gonsales, flew to the Moon on a flimsy raft
towed by trained swans.  This feat was really quite accidental, for
Gonsales had merely been attempting the conquest of the air, not of
space.  But he did not know that his swans had the habit, hitherto
unrecorded by ornithologists, of migrating to the Moon.  His
involuntary flight to our satellite occupied twelve days, and he had no
difficulty with breathing on the way.

However, he did notice the disappearance of weight as he left the
Earth, and on reaching the Moon discovered that its pull was much
weaker, so that one could jump to great heights.  This idea is now
quite familiar to us, but

Godwin was writing fifty years before Newton discovered the law of
gravitation.

The idea of lunar voyages was now becoming popular, and in 1640 Bishop
Wilkins published a very important book, A Discourse Concerning a New
World.  This was not fiction, but a serious scientific discussion of
the Moon, its physical condition, and the possibility that it might
have inhabitants.  But Wilkins went further than this, for he concluded
that there was no reason why men should Dot one day invent a means of
transport-a "flying chariot," as he called it-which could reach the
Moon.  He even suggested that colonies might be planted there, a
proposal which, needless to say, caused some foreign writers to make
rude remarks about British imperialism.

During the next two centuries there was a steady trickle of books about
space flight.  Some were pure fantasy, but others made at least
occasional attempts to be scientific.  Undoubtedly the most ingenious
writer during this period was Cyrano de Bergerac, author of Voyages to
the Moon and Sun (1656).  To Cyrano must go the credit for first using
rocket propulsion, even though he certainly had no idea of its
advantages.  Still more surprising, he anticipated the ramjet.  In his
last attempt at interplanetary flight, he evolved a flying machine
consisting of a large, light box, built of convex lenses to focus
sunlight into its interior.  The air, being thus heated, would escape
from a nozzle and propel the machine skyward.

Although most of the stories of this era were concerned with voyages to
the

Moon (and sometimes to the Sun, which was also believed to be a
habitable world), some writers' imaginations did go a little further
afield.  Thus

Bernard de Fontenelle, in 1686, wrote a widely read book on popular
astronomy, A Plitrality of Worlds, in which He maintained that all the
planets were inhabited by beings who had become suitably adapted to
their surroundings.  And in 1752 the great Voltaire produced
Nficrontegas, a work which is remarkably modern in outlook, as it shows
man and his planet in the correct astronomical perspective.  Micromegas
was a giant from the solar system of

Sirius who visited Earth with a companion from Saturn.  Like so many
works of its kind, before and after, Micromegas was used chiefly as a
vehicle for satire.

By the dawn of the nineteenth century, however, the space-travel story
had run into trouble.  Too much was known about the difficulties and
objections to interplanetary flight, and science had not yet advanced
far enough to suggest how they might be overcome.  The invention of the
balloon in 1783 had diverted attention to atmospheric travel and had
also shown conclusively that men could not live unprotected at great
altitudes.  The

Moon and planets had become much less accessible than they had seemed
to bishops Godwin and Wilkins.

By the second half of the century, however, the fiction writers had
overcome their momentary embarrassment, and stories of space travel had
become both more common and more scientific.  No doubt the great
engineering achievements of the Victorian age had produced a feeling of
optimism: so much had already been accomplished that perhaps even the
bridging of space was no longer a totally impossible dream.

This attitude is apparent in Jules Verne's famous story From the Earth
to the Moon (1865).  Although much of it is written facetiously-Verne
gota good deal of fun out of caricaturing the go-getting Americans who
were so anxious to reach the Moon-this work is important because it was
the first to be based on sound scientific principles.  Verne did not
take the easy way out and invent, as so many writers before and since
have done, some mysterious method of propulsion or a substance that
would defy gravity.  He knew that if a body could be projected away
from the Earth at a sufficient speed it would reach the Moon; so he
simply built an enormous gun and fired his heroes from it in a
specially equipped projectile.  All the calculations, times, and
velocities for the trip were worked out in detail by Verne's
brother-in-law, who was a professor of astronomy, and the projectile
itself was described in minute detail.  One of its most interesting
features was the fact that it was fitted with rockets for steering once
it had reached space.  Verne understood perfectly well-as many people
at a much later date did not-that the rocket could function in an
airless void, but he never thought of using it for the whole trip.

It is probable that Verne really believed that his space gun would
work, though we know now that the projectile would have been destroyed
by air resistance before it left the barrel.  On the other hand,

Verne can hardly have imagined that his travelers would have survived
the initial concussion, which would have given each of them an apparent
weight of several thousand tons.  No doubt he passed off this minor
point with a light laugh for the sake of the story.

Verne never landed his heroes on the Moon, perhaps because He was
unable to think of any way in which they could return safely.  Instead,
they performed a circumnavigation and then came back to earth-landing
in the ocean, as the Mercury and Gemini astronauts were to do exactly
one century later.

Many writers have pointed out Verne's prescience in siting his space
gun at

Tampa, Florida, barely a hundred miles from Cape Kennedy.  But he did
even better than this, for after discussing the areas of the United
States over which the Moon passed in its orbit, he decided that the two
most suitable states for the project were Florida and Texas.  So, a
century ago, he had their legislatures fighting each other for the
privilege (and profit) of running a space program.  Echoes of this
battle still roll around Congress from time to time.

Finally-and this is almost more uncanny-the 1865 American space effort
was managed by the dun Club of Baltimore.  It was in Baltimore, between
1955 and 1958, that the hardware for the first United States space
project (Vanguard) was built by the Martin Company.  But I would not
for a moment suggest that the following passage from the very first
page of From the

Earth to the Moon could conceivably apply to any space-oriented
activities in Baltimore, still less in Washington:

Now when an American has an idea, he directly seeks a second American
to share it.  If there be three, they elect a president and two
secretaries.

Given four, they name a keeper of records, and the office is ready for
work; five, they convene a general meeting, and the club is fully
constituted.  So things were managed in Baltimore..  ..

Verne's novel was an instantaneous success and has remained in print
even to this day.  It started a minor avalanche of imitations and
probably influenced the American writer Edward Everett Hale a few years
later.  His short story The Brick Moon, published in the Atlantic
Monthly (1869-70), appears to be the first treatment both in fiction
and nonfiction of the artificial satellite.

The Reverend Hale (he later became the first, and doubtless the last,
science-fiction writer to be chaplain to the U.S. Senate) proposed the
construction of his brick moon for reasons that are surprisingly
modern, ninety years afterward, the Transit program was to prove their
soundness.

He pointed out that a small but clearly visible body revolving around
the

Earth in a close orbit would be invaluable to navigators.  Given tables
showing the position of such a second moon at any time, one need only
take a simple observation of it with a sextant to determine one's
longitude.

Hale's idea, to put it crudely, was to hoist the Greenwich meridian
into the sky so that anyone could see it and so determine his location
on the

Earth.  The artificial moon would fulfill the same role for the
observation of longitude that the Pole Star does for latitude.

Though Hale's treatment of this theme was not altogether serious (much
of his story is written with the archly elephantine humor that
occasionally jars on most modern readers of Moby Dick), he had
obviously given a great deal of careful thought to the project.  He
decided that, in order to be visible through a telescope of modest
size, his satellite should be 200 feet in diameter.  And since a
satellite above the Greenwich meri dan would be visible over only a
part of the globe, there should be a second moon moving in another
orbit-say, one passing over New Orleans, the meridian of which is at
right angles to that of Greenwich.

So that it could be seen over a large area, the moon would also have to
be at a considerable height, and Hale suggested that an altitude of
4,000 miles would be a reasonable figure.  If it were too close, he
pointed out, it would spend much of its time eclipsed in the shadow of
the Earth.

To be of reasonable weight, the moon would have to be hollow, and Hale
proposed that brick would be a better constructional material than
iron, because it would withstand the heat of the satellite's friction
through the atmosphere.  This also shows remarkable foresight, since
ceramics of various kinds are now widely used as beat-resistant
materials for spacecraft.

The problem of getting the brick moon up into its orbit was one which
Hale solved in a very original fashion.  His heroes, who were
altruistically fired with a desire to save the thousands of seamen who
perish every year through errors in navigation, built two enormous
vertical flywheels.  These revolved, their rims nearly touching, in
opposite directions, being brought up to speed over a period of months
by water power.  When the brick moon was finished, it was to be:

gently rolled down a gigantic groove provided for it, till it lighted
on the edge of both wheels at the same instant.  Of course it would not
rest there, not the ten-thousandth part of a second.  It would be
snapped upward, as a drop of water from a grindstone.  Upward and
upward; but the heavier wheel would have deflected it a little from the
vertical.  Upward and northward it would rise, therefore, till it had
passed the axis of the world.  It would, of course, feel the world's
attraction all the time, which would bend its flight gently, but still
it would leave the world more and more behind..  .

The money to build the brick moon was raised by public subscription,
and the flywheels were constructed in a remote part of the United
States.  The moon itself was nota simple shell of masonry, but had its
interior divided into thirteen spherical chambers, in contact with each
other so that "by the constant repetition of arches, we should with the
least weight unite the greatest streng&"

However, things did not go quite according to plan.  One night, owing
to a ground subsidence, the brick moon was accidentally
launched-together with all the workmen and engineers who had decided
that its spacious chambers made better living quarters than their log
cabins.  Yet the story has a happy ending for all concerned (except
possibly the subscribers to the enterprise).  The thirty-seven men,
women, and children in the brick moon had survived their unscheduled
launching into space, and having large quantities of food (not to
mention a few bens) with them, had managed to establish a contented
little community.  They were able to signal to their friends on Earth
by making long and short jumps off the edge of their tiny world, thus
producing messages in Morse code that could be read through a
telescope.  They had no regrets at all for leaving the Earth, and the
moral that the author drew was: "Can it be possible that all human
sympathies can thrive, and all human powers be exercised, and all human
joys increase, if we live with all our might with the thirty or forty
people next to us?  ... Can it be possible that our passion for large
cities, and large parties, and large theaters, and large churches,
develops no faith nor hope nor love which would not find exercise in a
little 'world of our own'?"

Hale's story was published in 1869-70; seven years later, at the
Naval

Observatory in Washington, Dr.  Asaph Hall discovered that Mars had two
tiny satellites, one of which revolved around the planet more swiftly
than Mars turned on its axis.  He wrote to Hale, "The smaller of these
moons is the veritable Brick Moon."  One wishes that both author and
astronomer could have known that just eighty years later Earth was to
rival Mars in this respect.

The ubiquitous Jules Verne made a passing reference to artificial
satellites in one of his lesser works, The Begum's Fortune, published
in 1879.  This novel also contains a prototype of the mad scientist who
haunted (one might say infested) so much early science fiction but who
is fortunately now almost extinct.

The story concerns the rivalry between two cities, Stahlstadt and

Frankville, the nationalities of which should be obvious.  Stablstadt
was ruled by the demoniac Professor Schultz, whose main interest seemed
to be the invention of diabolical weapons of war.  His masterpiece was
a giant multiple cannon with the barrels nesting one inside the
other-an anticipation, in some respects, of the step, or multistage,
rockets of today.

This cannon was intended to destroy Frankville at one blow, but the
professor made one of those extraordinary oversights which characterize
his species.  (I have yet to encounter a mad scientist who was defeated
by the hero's brains rather than his own carelessness.) He had made the
cannon too powerful, and the shell reached such a velocity that it
never came down again but continued to circle the Earth.

In the first year of the twentieth century appeared what still remains
the finest of all interplanetary romances, H. G. Wells's The First Men
in the

Moon.  Like many of Wells's early novels, it is untouched by time, as
it encapsulates forever one moment in history, the last golden
afterglow of the Victorian age.  On the purely technical side, however,
"the book marks a retrogression from Verne,

whose space gun was at least plausible and founded on scientific facts.
To get his protagonists to the Moon, Wells invented "Cavorite," a
substance that could act as a gravity insulator.  His heroes had only
to climb into a sphere coated with this useful material and they would'
travel away into space.  To steer themselves toward the Moon it was
merely necessary to open a shutter in that direction.

This conception of a gravity-insulating or gravity defying substance
did not originate with Wells, and the first person who seems to have
employed it was one J. Atterley, whose Voyage to the Moon appeared in
1827.  Neither Mr.

Atterley nor any of his numerous successors ever explains, so far as we
are aware, how their antigravitational metals manage to stay on Earth:
one would have thought that materials with such a tendency to
levitation would long ago have departed into space.

It is not difficult to show that a substance like Wells's "Cavorite" is
a physical impossibility, defying fundamental laws of nature.  But the
idea of antigravity is not in itself absurd, and we sba ll return to it
in Chapter 24.

Wells's book appeared in 1901, and it would be difficult to count, let
alone read, the number of works that have since touched upon the
subject of interplanetary flight.  There are two very obvious reasons
for this increase.  In the first case, the conquest of the air had
acted as a stimulus to imagination; in the second, the foundations of
astronautics were being laid by competent scientists, and the result of
their work was slowly filtering through to the general public.  The
researches of Goddard (from 1914 onward) and later of Oberth had
focused attention on the rocket, and even before the modern era of
large-scale experimental work had proved the accuracy of these men's
predictions, the rocket had been accepted as the motive power for
spaceships in the majority of stories of interplanetary travel.  It can
hardly be doubted that these stories-and not merely those few with a
carefully scientific basis-have done a great deal to bring closer the
achievement of which they told.  When one considers it dispassionately,
it is a somewhat extraordinary situation.  Even the literature of
flight, which provides the closer parallel, is not nearly so extensive
or so carefully worked out.  The conquest of space must obviously have
a fundamental appeal to human emotions for it to be so persistent a
theme over such a span of time.

It is sometimes argued, by people who can know very little about either
science or science fiction, that the actual achievement of space travel
will mean the end of romances about the subject.  The reverse is more
likely to be the case.  True, "first-voyage-to-the-Moon" stories have
graduated from fiction to news; but the farther our frontier extends
into space, the greater the area of contact with the unknown.  When we
land on the Moon and really learn something about that strange and, it
now seems, exciting little world, there will be splendid opportunities
for stories about its remote past and its probable future; and the
planets, of course, will remain as a playground of the imagination for
decades to come.  The space-travel tales of the twenty-first century
will have the same hard core of realism that makes Wells and Verne so
much more satisfying than their unscientific predecessors.  The more we
really know, the greater is the scope for fiction; only feeble minds
are paralyzed by facts.

A little late in the day, scholars are now beginning to study the
interactions between science and literature; in her book Science and

Imagination, for example, Marjorie Hope Nicolson has pointed out the
tremendous impact made upon art and general culture by the inventions
of the telescope and the microscope.  This is a theme to which we shall
return in Chapter 30, when the philosophical and cultural effects of
astronautics will be discussed.

It is surely only a matter of time before artists, writers, and
musicians express their reactions to man's newest conquest of his
environment.  From the exploration of.  space has already come such a
flood of knowledge as the world has never before seen.  But that is not
enough, for without feeling and emotion, knowledge alone is no more
than a weariness of the soul.

FROM FANTASY TO SCIENCE

All men dream; but not equally.  Those who dream by night in the dusty
recesses of their minds wake in the day to find that it was vanity; but
the dreamers of the day are dangerous men for they may act their dream
with open eyes, to make it possible.

T. E. LAWRENCE-The Seven Pillars ol Wisdom

'ihere was a time, just before Sputnik 1, when Soviet claims to
priority in any field of science or invention were treated with amused
skepticism.

Sometimes this was justified; but in the case of astronautics, there
can be no doubt that credit for first working out the scientific
principles of space flight goes to Konstantin Tsiolkovsky.  His
pioneering mathematical papers on the subject were written in the
1880's and were first published in 1903, the very year in which the
Wright brothers flew.

Tsiolkovsky was a shy, deaf schoolteacher-although, as in the case of
that other inventor Thomas Edison, his deafness was probably far from
being a complete disadvantage.  He was born in September, 1857, and it
is no coincidence that the Soviet Union launched its first satellite
within a few days of his centenary.

At the age of fourteen Tsiolkovsky became interested in aviation and
conceived the then-daring idea of the all metal dirigible.  This led
him on to thoughts of space flight, and to quote his own words: "There
was a moment when it appeared to me that I had solved this Droblem fat
sixteen].

I was so excited that I could not sleep the whole night, and instead
spent it wandering through the streets of Moscow and thinking about the
great consequences of my discovery.

Toward morning, I was convinced of the fallacy of my invention.  I
still remember that night, and even now, fifty years later, I sometimes
dream about rising in my machine toward the stars and feeling the same
elation."

The sixteen-year-old Tsiolkovsky's mistake lay in thinking that one
could use centrifugal force for propulsion.  As we shall see later,
this is a common error and crops up, even today, among the
perpetual-motion-mac bine fraternity.  He quickly set himself on the
right track and realized that the rocket was the only means of
providing thrust in the vacuum of space.

By 1898 he had derived the fundamental laws of rocket propulsion (see

Chapter 7).  He was the first man in history to understand the true
scale of the problem involved in escaping from Earth.

Working under great difficulties, with pitifully meager resources,

Tsiolkovsky calculated, made models in his little workshop, and wrote
numerous popular and technical articles advocating his ideas.  Not only
were most of these soundly based; they were also so astonishingly ahead
of their time that even now we are still catching up with him.  To
quote from

Academician M. E. Tikbonravov's preface to the collected works (Moscow,
1964): "Tsiolkovsky dreamed of sending mankind to the entire solar
system; he dreamed of the possibility of a total realization of solar
energy; he dreamed of a more comfortable life in a medium without
gravity and of cities in interplanetary space."

Besides anticipating and solving in principle almost al the engineering
difficulties of space flight, Tsiolkovsky also applied himself to the
biological problems.  He discussed immersing astronauts in water to
reduce the effects of acceleration at takeoff; he designed centrifugal
showers so that they could bathe in the absence of gravity; he
considered growing plants in cosmic "greenhouses" to purify the air and
to provide food; he looked into the design of space suits.  Most of
these concepts are now so familiar to us that it is hard to realize
that someone first had to invent them; that someone was usually
Tsiolkovsky.

In his attempt to spread his ideas as widely as possible, Tsiolkovsky
wrote several works of science fiction, with such titles as "The Year
2000" and

"The Conquest of the

Solar System."  Most of these were never published (or indeed
completed) ; an exceptimi is the naive but fascinating novel Beyond the
Planet Earth, which first appeared in 1918.  Many years later, in 1933,
Tsiolkovsky became involved in a Soviet motion picture, Cosmic Voyage,
and made numerous drawings for it, but nothing came of the project.  He
was perhaps luckier than Hermann Obertb, whose experience five years
earlier with the Fritz

LangUFA movie Girl in the Moon was far from happy.

Tsiolkovsky's work was little known outside his own country until it
was discovered by the rest of the world in the 1930's.  It is greatly
to the credit of the struggling new Soviet state that, after the
revolution, He received support and modest acclaim; when He died in
1935, his home town,

Kaluga, gave him a lavish state funeral and erected an impressive
monument in his honor.

His greatest monument, however, is one that appropriately enough had
never been seen by human eyes before it was discovered by Lima 3 on the
far side of the Moon.  It is the giant crater, one of the most
extraordinary of all lunar formations, that now bears his name (Plate
3).  This astronomical immortality would, one feels, have left
Tsiolkovsky pleased, surprised, and more than a little embarrassed.

The second pioneer, in order of time, was the New, England physics
professor Robert Hutchings Goddard, born in Worcester, Massachusetts,
in 1882.  As a boy, Goddard had his imagination fired by the stories of
Verne and Wells.  In his autobiography, he recalls an incident at the
age of seventeen that bears a striking resemblance to Tsiolkovsky's
moment of revelation; even the basic error was the same:

On the afternoon of October 19, 1899, I climbed a tall cherry tree at
the back of the barn and, armed with a saw and a hatchet, started to
trim the dead leaves from the tree.  It was one of those quiet,
colorful afternoons of sheer beauty which we have in October in New
England and, as I looked toward the fields to the east, I imagined how
wonderful it would be to make some device which had even the
1)ossibility of ascending to Mars, and how it would look on a small
scale if sent up from the meadow at my feet.

It seemed to me then that a ~weight, whirling around a horizontal shaft
and moving more rapidly above than below, could furnish lift by virtue
of the greater centrifugal force

Plate 3. Tsiolkovsky Crater, on the Far side at the Moon.  Photographed
by

Lunar Orbiter 3 on February 19, 1967.  NASA at the top of the path.  In
any event, I was a different boy when I descended the ladder.  Life now
had a purpose for me.  Later in the year, I started making wooden
models in which lea4 weights were to furnish lift by moving back and
forth in Yertical ari-s, or strike against metal pieces as they whirled
around b,orizontal arcs.  These naturally gave negative results, and

I began to think that there might be something after all to Newton's
Laws.  .

Goddard realized that if he hoped to make any progress, he would have
to master physics.  and mathematics.  This He did- to such effect that
he obtained his Ph.D. at Clark University, Worcester, where he was also
to spend all his academic career.  By 1909 he had worked out the theory
of the multistage (step) rocket, and in a series of more than two
hundred patents from 1914 onward he covered almost every conceivable
aspect of rocket design, propulsion, and guidance.

Unlike Tsiolkovsky, Goddard had the resources to do a considerable-for
that time-amount of experimenting.  By 1916 he had demonstrated that
his theories were sound and had shown by actual tests that rockets gave
a greater thrust in vacuum than in air.  (There had never been any
theoretical doubt of this, but even at a much later date skeptics still
refused to believe it.)

Goddard's eyes were clearly focused on the Moon and planets; in his
private notebooks he discussed refueling spacecraft from hydrogen and
oxygen produced on the Moon, electrical propulsion, atomic power,
reconnaissance of the planets by automatic cameras, and similar highly
advanced ideas.  But he was also a cautious and practical man, and when
the time came to draw up a prospectus of his future plans he
concentrated on a discussion of atmospheric sounding rockets, which he
gave the innocuous title A Method of

Reaching Extreme Altitudes.  Not until the last few paragraphs would
the intrepid reader learn that "extreme" could mean "infinite."

This manuscript secured a grant of $5,000 from the Smithsonian
Institution, which published it in 1920.  Goddard was thus able to
increase tLc scope of his experiments, and on March 16, 1926, he flew
the world's first liquid-rocket-propelled vehicle in a field near
Auburn, Massachusetts.  This flimsy contraption was airborne for just
over two seconds, reached an altitude of 40 feet and a speed of 60 mph,
and was the direct ancestor of all the giants of today.

In 1929 a successful flight by a somewhat larger rocket, whose peak
altitude was no less than 90 feet, caused so much noise that the whole
neighborhood was disturbed, and the police were deluged by reports of
crashing airplanes.  Goddard was forbidden to conduct any more flights
at

Worcester, but this temporary setback proved to be a blessing in
disguise.

The resulting publicity came to the attention of Charles Lindbergb,
then at the height of his fame.  The aviator visited Goddard, discussed
his work, and immediately realized its importance.  He recommended
support for it from the Guggenheim Fund for the Promotion of
Aeronautics, which subsequently arranged a grant of $50,000.

Now, for the first time, Coddard was able to devote himself entirely to
rocketry.  He established a workshop and launching tower near Roswell,
New

Mexico, not far from the White Sands Proving Ground, where, less than
a

Plate 4. Robert H. Goddard and one of his rockets.

Courtesy of Mrs.  Esther C. Goddard year after his death, the first
Americanized V-2's were to roar into the sky.

At Roswell, with the aid of his wife, Esther, and a handful of
assistants,

Goddard built, tested, and flew a whole series of increasingly advanced
rockets between 1930 and 1941.  Although the greatest height reached
was only 9,000 feet, they represented an astounding achievement.  When
one looks at the Goddard exhibit in the National Aerospace Museum,
Washington, it is almost impossible to believe that a single man should
have attempted to develop such complex systems.  Today's rocket
designers have thousands of subcontractors who can deliver practical I
ly any component straight off the shelf; God dard had to build almost
everything in his own workshop.

Little wonder that to the outside world his progress seemed agonizingly
slow and that he was sometimes criticized by other rocket enthusiasts
for not publishing or exchanging information.  Any such exchange would
have been rather a one-way business, and Goddard's reticence was
increased by garbled and often facetious press coverage.  (Once you
have announced that it is possible to reach the Moon, of course,
everything you launch is a "failure" if it doesn't get there.)
Moreover, his long series of patents proves that he knew exactly what
he was doing; after his death Mrs.  Goddard (who had acted as his
photographer, secretary, and archivist) and the Guggenbeirn

Foundation were jointly awarded $1 million by the Department of Defense
for their use-the largest patent settlement on record.

It has often been suggested that Goddard would have made more rapid
progress, and history might also have been changed, if he had received
more money or technical assistance.  Mrs.  Goddard does not think that
this would have made a great deal of difference; additional funds might
have helped, but on the whole, except for two years lost during the
Depression, the grants Goddard received were adequate for his scale of
operation.  She once remarked to me that a really large sum of money
would have swamped their little team; Dr.  Goddard would have spent all
his time dealing with accounts, preparing budgets, hiring and firing,
answering auditors' queries, testifying before Congress.... By avoiding
all this, he was a lucky man-and a happy one.

Moreover, like most pioneers, Goddard was a "loner."  Though He was wit
tv and cultured and enjoyed social life, in his creative work he was,
like

Newton, 11 sailing strange seas of thought-alone."

One well-known American rocketeer who volunteered his assistance did
not get very far.  I have received piquant accounts, from both
surviving principals, of a visit to Roswell by an enthusiastic young
aeronautical engineer in 1936.  The Goddards, he says, received him
cordially, but never once were the dust sheets removed from the large,
torpedo-shaped object that lay in full view of his vainly goggling
eyes.

After Goddard's death, on August 10, 1945 (he lived

Front Fantasy To Science 9 37 just long enough to examine, in a
captured V-2, the large-scale realization of his concepts) the range of
his vision was slowly appreciated.  Today innumerable institutions,
awards, banquets, and other functions bear his name.  There is the
Goddard Space Flight Center near Washington, the Goddard Medal of the
American Institute of Aeronautics and

Astronautics, the annual Goddard Symposium of the American

Astronautical Association, and even Goddard Day (March 16).* At

Clark University, where he spent so many years as student, graduate,
and professor, a splendid Goddard Memorial Library has been
established, thanks to a fund-raising drive sponsored by one of his
greatest admirers, Dr.  Wernher von Braun.  It was also

Dr.  von Braun who started the successful agitation to have a stone
marker placed at the site of the first liquid-fuel rocket launch.

And one day, it can hardly be doubted, Robert Hutchings Goddard's name
will join Tsiolkovsky's on the far side of the Moon.

While Goddard was preparing his first Smithsonian paper, a young

German-Hungarian student named Hermann Oberth was also thinking of
space travel.  Quite independently of his two precursors, he had
covered much the same ground; He had even fallen into the identical
"centrifugal-drive" trap that seems to lurk in ambush for amateur
astronauts.  ("Every year,"

Oberth has since reported, "I am approached by eight or ten inventors
with what amounts to the same scheme."  And not long ago, the editor of
a leading

American science-fiction magazine, who should have known better, gave
publicity to a similiar 9 proposal.)

It was Jules Verne's Moon novel that set Oberth thinking about rockets,
at first as a means of steering in space.  However, he slowly realized
that they could perform the whole mission, not merely the minor job of
course correction.  I should tell a lie," Obertb has written, "in
stating that I was delighted with this discovery.  I was not pleased at
all with the enormous fuel consumption, the hazards of rockets
containing solid fuels, the difficulty of handling liquid fuels,
etc."

0 It is ironic to note that the first Goddard Professor of the
California

Institute of Technology, the brilliant Hstie-Shen Tsien, is now in
charge of the Chinese rocket program.  For an account of the almost
incredible events in the McCarthy Era which led to this disaster, see
"The Bitter Tea of Dr.  Tsien," Esquire Magazine, September, 1967.

Realizing that practical experiments were far beyond the means of a
young mathematics teacher, Oberth concentrated on theoretical studies.
By 1923 he had derived the basic equations of rocket flight and had a
very clear idea of the speed, fuel requirements, and general
engineering principles of spacecraft capable of traveling beyond the
atmosphere.

At his own expense, he published his results in a slim brochure
entitled

"The Rocket Into Planetary Space" (1923); he was quite unaware, then,
that

Tsiolkovsky had covered much of the same ground twenty years before.
(Later, the two men exchanged friendly greetings and copies of their
publications.) The scientific establishment, as might be expected,
ignored

Oberth's work almost completely.  Those few academicians who deigned to
notice it could find no flaws in the calculations, but that did not
deter them from pronouncing them "obviously" absurd.

Despite this, Oberth's views attracted a great deal of attention in the
defeated and impoverished Germany of the 1920's; the psychological
reasons for this (escapism?) might be worth investigating.  His views
were widely popularized by a number of young science writers, notably
Willy Ley, and in 1929 he expanded them into a formidable volume
entitled Wege zur

Raumschiflahrt (The Road to Space Travel).

After a brief discussion of automatic rockets, Oberth quickly got on to
the subject of manned vehicles, and in particular, "space stations" in
orbit around the Earth.  Among their uses he considered meteorological
observations, military reconnaissance, the mapping of unexplored
places, iceberg warnings (the Titanic disaster, which Obertb
specifically mentions, was still fresh in mind), and the establishment
of communications (by heliograph) between isolated spots on the
Earth.

Perhaps most important of all, Oberth pointed out the enormous value of
space stations as refueling bases for interplanetary expeditions.  His
most imaginative suggestion, however, was the proposal that huge
mirrors be constructed in space to reflect sunlight to the Earth. Owing
to the weightless conditions that prevail in free orbit, it would be
possible to build mirrors literally miles in diameter from quite modest
amounts of material.  Such reflectors could produce alterations in the
intensity of sunlight over large areas of the Earth, thus preventing
frosts, controlling winds, and making the polar regions habitable. 
(Another use was proposed forty years later.  In 1966 the U.S.
Department of Defense asked five aerospace companies to look into the
question of orbital mirrors for tactical military
purposes-specifically, for illuminating the jungles of

Vietnam at night.)

All this was very exciting, and in 1925 Oberth's ideas led directly to
the founding, by a group of young German enthusiasts, of the Verein
ffir

Raumschiffabrt (literally, "Society for Spaceship Travel," though it is
usually referred to as the German Rocket Society).  The vicissitudes of
this organization, and Oberth's tragicomic entanglement with the UFA
movie company's The Girl in the Moon, have been well documented in
Willy Ley's standard history, Rockets, Missiles, and Space Travel.
Before time ran out, and the Nazis marched in, the VfR had succeeded in
launching several types of small liquid-propelled rockets and
recovering them by parachute.  There was nothing here that Goddard had
not already done, but his work was still virtually unknown, whereas the
German experiments were conducted in a blaze of publicity.  The
impecunious rocketeers cannot be blamed for this; it was the only way
they could raise money.

Not surprisingly, their work also attracted the attention of the
German

Army, then looking for weapons that were not banned under the Treaty
of

Versailles.  When that document was drawn up, no one had taken rockets
seriously, an error which was to be repeated many times in the decades
ahead.

As an unfortunate but perhaps inevitable consequence, man's first steps
into space were taken under military sponsorship.  Not until the Saturn
I's and 5's of the 1960's were any really large rockets developed for
purely peaceful objectives; and even here the underlying motivation was
not entirely scientific.

Of the three "classical" writers on astronautics, only Hermann Oberth
lived to see the full attainment of his dreams.  But as he was
primarily a theoretician, and nota practical engineer, he had to watch
others turn them into reality.  Although He eventually joined the
Peenemiinde staff, the V-2 had already been developed by the time he
was able to obtain his security clearance.  Then, to make the irony
complete, he was set to work on solid-propellant anti-aircraft
rockets.

In 1955 he came to the United States to join the

Redstone group but was able to stay only a few years before he had to
return to Germany in order to claim his teacher's pension.  He then
went to live in retirement near Nuremberg, but from time to time he
emerges in somewhat dubious political company.

I last glimpsed this strange and brilliant man in circumstances that
neatly summed up the frustrations of his life.  He was one of a crowd
of visitors being conducted through the great space center that now
bears the name of

Robert Hutchings Goddard.  None of the young scientists who were acting
as guides recognized him; I wondered how many of them even knew his
name.

"NOTHING TO PUSH AGAINST"

There was a time, not very long ago, when any writer or lecturer on
space flight had to devote a good deal of effort to convincing his
audience that rockets could provide thrust in the vacuum of space,
where, obviously, there is 1. nothing to push against."  This
infuriating phrase-so true, yet so misleading-is seldom heard now that
the capabilities of rockets in space have been amply demonstrated.
Nevertheless, most people would probably find it very hard to explain
how a rocket does manage ~o function in a medium where all other forms
of propulsion are useless.

It is no answer to say glibly, as do some writers, that the rocket
operates by "pure reaction."  Every form of propulsion does that; it is
impossible to conceive, even by the wildest flight of imagination, of
one that does not.

A reaction is simply an opposing thrust or force.  When a man walks,
the friction between his feet and the ground makes the Earth move
backward, ever so slightly.  If there were no reaction-if, for. 
example he were standing on a sheet of completely frictionless
ice-there could be no movement.

So it is with automobiles, ships, and aircraft.  They all react,
through tires, screws, or propellers, on the medium that supports them.
This fact was first clearly recognized by Sir Isaac Newton and embodied
in his third law of motion-"To every action there is an equal and
opposite reaction"-a statemen~, , 4such deceptive simplicity that it
may seem self-evideni... This equality of action and reaction is
universally true, but in most of the cases in everyday life we are
aware of only the action; the reaction is un observable  Why this is so
is obvious when one considers the case of a man jumping.  He imparts an
equal reaction to the Earth; but as the mass of the Earth is about 100
sextillion (100,000,000,000,000,000,000,000) times greater than his,
the velocity he gives to it is smaller in exactly the same ratio.  Only
in rather exceptional or dramatic cases is the reaction obvious; the
most familiar example is the recoil produced by the firing of a gun.
But whether it is obvious or concealed, the reaction is always there,
and no movement of any kind is possible without it.

We can best visualize the mode of operation of a rocket by considering
what

Einstein used to call a "thought experiment," an experiment which no
one would actually perform but which illustrates some principle.
Imagine a man on a light sled, which also carries a large pile of
bricks, and assume that the sled is resting on a sheet of smooth,
absolutely frictionless ice.

The man takes one of the bricks and throws it horizontally.  Newton's
third law (and common sense, which is not always wrong) tells us that
the action of throwing the brick produces an equal reaction on the
sled.  But because the sled (plus cargo) weighs much more than the
brick, it moves off at a correspondingly smaller velocity.  Again,
there would be an exact proportionality.  If the vehicle's weight was a
hundred times that of the brick, it would move at one-hundredth of its
velocity.

However, this velocity would not be lost, since we have assumed that
the ice is completely frictionless.  Even if the sled's acquired speed
were only a few inches a minute, it would retain this speed
indefinitely.  (We are also, of course, assuming that there is no air
rqistance.)

Now the passenger throws away another brick, at exactly the same
velocity as before.  The speed of the sled at once jumps again, but by
a fractionally greater amount this time, for it is now a little hilbter
owing to the loss of the first brick.  And as more and more bricks are
thrown overboard, it will continue to gain speed, each time by a
slightly greater amount as its mass diminishes.

We can learn several important lessons from this simple analogy; in
fact, it teaches almost everything that is necessary to know about
rocket propulsion.

xv __

N,

Fig 1. The rocket principle.

First of all, it is obvious that what happens to the bricks after they
have left the sled does not matter in the least; all the recoil or
thrust is produced during the act of throwing.  The bricks could sail
on forever or could crash into a wall six inches away-it would make no
difference to the sled.  The method of propulsion is, therefore,
independent of any external medium.

As the bricks are used up, so the weight of the vehicle steadily
diminishes.  (To forestall objections from purists: the words "weight"
and "mass" are used interchangeably here, as there is no need to make
the distinctions that will be necessary later.) The last bricks will,
therefore, produce much greater effect than the first; ond the
difference can be very large if the mass of the sled has been
siibstantiallv reduced.

If the "empty" weight of the sled is on1v half that of its full weight,
the very last brick will produce twice the gain in speed of the first
one.

Consequently, not only does the sled's velocity increase during the
experiment, its acceleration does so as well.

The analogy with the rocket should now be clear, the main difference
between the two cases being that a rocket ejects matter continuously
and not in separate lumps, so that it produces a ste adv thrust instead
of a series of jerks.  If the man on the sled were pumping water out of
a nozzle, the analogy would be exact.

Thus it is possible to have a completely self-contained propulsion
system that can operate in a vacuum.  Yet, though the logic is
impeccable, for a long time even highly qualified engineers and
scientists remained unconvinced.  They felt in their bones-and some
readers may svmoathize-that though such arguments were sound for
devices that ejected solid masses, like the sled discussed above, they
did not apply to a rocket that released a 11 mere" stream of gas into
an infinite vacuum.  In fact, some savants denied that any combustion
was -oossible in these circumstances; it was for this reason that
Goddard went to the trouble of firing small rockets in vacuum chambers.
This did not stop the New York Times from printing an editorial in
1920.  in which it exnressed bowes that a professor at Clark

College was only pretending to be ignorant of elementary physics.  if
he thought that a rocket could work in a vacuum The writer would
doubtless have been surmised to know that one day the Times would
receive the National

Rocket Club's award for aerospace reporting-at the Robert H. Goddard

Memorial Dinner.

The critics overlooked the fact that mass is mass, whether it be in the
form of solid lumps or the most tenuous vapor.  If the bricks in our
thought experiment were ground into fine sand before being ejected, it
would make no difference to the result.  Similarly if they were
volatilized, the final speed of the sled would be exactly the same as
before, provided only that the ejection speed of the material remained
unaltered.

So the answer to the old question, "What does a rocket push against?"
should now be obvious.  It pushes against its own combustion
products.

A further and more subtle question is then often asked: "Just where
inside the rocket is the thrust developed?"  Essentially, a rocket
motor-and this is true whether it is solid- or liquid-fueled-consists
of an enclosed space (the combustion chamber) containing hot, expanding
gases which can escape in only one direction, through a nozzle or
orifice.

For simplicity, suppose that the combustion chamber is spherical (which
is actually the case for some high efficiency solid rockets) and that
there is at first no orifice; the chamber is completely sealed.  The
combustion products are then unable to escape, and they produce the
same thrust over the entire interior surface of the sphere.  All forces
balance out and so (assuming that the chamber does not burst) there is
no movement in any direction.

Now pierce a hole in one side of the chamber.  The pressure exactly
opposite this hole will be unbalanced; there will therefore be a net
force producing movement

* I have been mean enough to reprint this editorial, despite Mrs.
Goddard's kindhearted protests, in The Coming of the Space Age (Des
Moines: Meredith, 1967).

"Nothing To Push Against" e 45

0 D C+

(a) (b)(C)

Fig.  2. The lorces in the rocket engine.

toward the left.  The other forces will still cancel each other, and
their only effect will be to exert pressure on the wall of the chamber,
which must therefore be built strongly enough to withstand them.

The situation shown in Figure 2 (a) and (b) is that reproduced in the
familiar experiment of blowing up a balloon, releasing the neck and
letting it jet around the room.  This demonstration, though perfectly
sound, is not really convincing; a skeptic could always argue that the
balloon's gyrations were produced by reaction against the air.

A simple hole like that shown in (b) would result in a highly
inefficient performance; most of the escaping gas would expand sideways
and do no useful work.  Matters can be much improved by the addition of
a nozzle (c); when the released gases expand, they press against it as
shown, and so provide additional thrust.

Anyone who has followed this argument should now understand that all
the thrust of a rocket is generated inside the combustion chamber and
nozzle and that any surrounding medium plays no essential part in the
process.

This is not to say, however, that it has absolutely no effect on the
performance of a rocket motor.  When any rocket flies inside the
atmosphere, the surrounding air actually hinders the expansion of the
exhaust gases.

For this reason the thrust of a rocket increases by 10 per cent or more
as it leaves the atmosphere and enters the vacuum of space the only
environment where it can function with full efficiency.

It also follows-and this is perhaps even harder to accept-that a rocket
gets no additional thrust at takeoff if the jet impinges on some fixed
object, such as the ground or the launching pad.  Indeed, this must be
avoided at all costs, since the reflected stream of hot gases can cause
great damage to the vehicle.

Almost all rockets that have been built so far have obtained their
thrust from chemical reactions; burning substance", have generated hot
gases that escape from a nozzle.  However, there are endless ways of
producing the same effect: any power source may be used, from a nuclear
reactor to an electric battery.  And any material may be used to
provide the jet: solids, liquids, gases, electrons, ions, subatomic
particles.  As long as they have mass and can be air ned in a definite
direction, they will give thrust.

Perhaps in the far future there may be spacecraft propelled by the
swiftest "jet" that can exist-beams of pure light of unimaginable
intensity, created by generators brighter than a billion suns.  But
they will still be rockets, in the direct line of descent from the
crude vehicles which, in our time, first broke through the barrier of
the atmosphere.

POWER FOR SPACE

By the early 1930's there was plenty of rocket theory but very little
practice.  Though a few small test vehicles had flown, their
performance had not been impressive, especially when set against talk
of travel to the Moon and planets.  Most people who beard that
Goddard's rockets had ascended a few thousand feet probably reacted in
the same way as the shortsighted but typical newspaper editor who said
of the Wright brothers' first bop off the ground: "57 seconds?  If it
had been 57 minutes, that might have been news."

What the skeptics failed to realize was that, even when the basic
theory is completely sound, it requires millions of man-years and
billions of dollars to develop a new technology.  A man like Goddard
could design an entire rocket vehicle, and it might seem to the layman
that all that then had to be done was to send the drawings to the
workshop.  But it is not as easy as that; even the simplest
liquid-propellant rocket contains dozens of components, all of which
have to function perfectly, and most of which have to be specially
built.  Apparently straightforward devices such as valves to control
the flow of propellants, gyroscopes for steering, pumps for feeding
fuel into the combustion chambers, and reliable parachute-ejection
mechanisms may demand months of development and dozens of tests.  When
one considers the mishaps that have plagued programs with virtuallv
unlimited funds and manpower, it seems a miracle that any of the
pioneering experimenters ever got their rockets off the ground.

As is well known, rockets fall into two distinct categories, one based
on solid, the other on liquid propellants.  47

"Solid" rockets, of which the ordinary back-garden, or Fourth of July,
fireworks are the most familiar examnle, have been in existence for
many centuries.  Precisely how long is still a matter of debate, but
they were certainly recorded in Chinese literature around A.D. 1200.

Although it has been said that the Chinese invented gunpowder and
proved their culture by using it only for fireworks, the rocket refutes
this, for they emPloyed it with great effect against the Mongols at the
siege of

K'aifungfu, north of the Yellow River, in 1232.  News of the invention
reached Europe very quickly, and the rocket was soon in common use both
as a work and as an impressive but usually unreliable weapon.  It was
not until the end of the eighteenth century, however, that its military
application was taken very seriously in the Western world.  Then, once
again, the demonstration came from the Orient, when the Indian prince
Tipu

Sahib of Mysore used it against the British at the Battle of
Seringapatarn (1792).  Although Tipu lost (his opponent, Charles
Cornwallis, was rather luckier than at Yorktown eleven years earlier),
the havoc wrought by his rocket artillery created a great impression.
It came to the notice of

Colonel William Congreve (not to be confused with the dramatist of the
same name) who developed large war rockets with ranges of more than a
mile and weights of tip to 42 pounds.  For a while it seemed that the
rocket might replace the gun, as indeed Congreve believed that it
would, but the great improvements in artillery soon made it obsolete,
except for campaigns against ill-equipped natives.

In the meantime, however, it had found another use, as a launcher of
rescue lines to ships stranded offshore.  Between 1850 and 1940 the
rocket was used almost exclusively for pyrotechnics and lifesaving; if
the totals could be added up it might yet turn out that the rocket has
saved more lives than it has taken.

No simpler propulsive device than a solid-fueled or powder rocket can
be imagined.  Even today its simplicity enables it to hold its own in
many applications, such as the Polaris and Minuteman missiles, although
these involve a fantastic degree of chemical, engineering, aerodynamic,
and electronic sophistication.  By trial and error, over a period of
centuries, the classical design shown in Figure 3 was evolved.

Black powder

Steel case N

Fig.  3. Solid-propellant rockets (a) firework, (b) modern solid.

The propellant was a slow-burning form Of gunpowder known as black
powder, the composition of which is roughly 60 per cent saltpeter
(potassium nitrate), 25 per cent charcoal, and 15 per cent sulfur; note
the crude nozzle and the internal-combustion chamber formed by the
conical space in the hard-packed powder charge.  Stability in flight
was maintained-if at all-by the trailing stick.

Cheapness and ease of manufacture were the two merits of this design;
in almost every other respect it was deplorable, and as a means of
carrying substantial payloads any distance it was useless.  One obvious
improvement was to remove the dead weight of the stick and to obtain
stability by small fins or canted exhaust nozzles, which made the
rocket spin in flight like a rifle-bullet; but graver defects were not
so easily remedied.  The most serious-for a device which is to be used
as a propulsive engine, not as a missile-is lack of controllability.
Once started, the powder will burn until it is all used up.  The
acceleration produced is also extremely high, so that the rdeket
reaches maximum speed very quickly and then wastes all its energy
against air resistance.

But a much more fundamental objection to the classical powder rocket is
that its propellants are really very feeble.

It was a long time before this was appreciated, because the spectacular
performance of an ascending rocket gives an impression of great
energy.

And yet, pound for pound, such mixtures as ordinary gasoline or
kerosene, with the correct proportions of oxygen, give several times
the energy of gunpowder.  True, they do not burn so rapidly, but that
is also an advantage, for the last thing wanted is in explosion.  On
the contrary, what is desired is a controlled release of energy, and
preferably a reaction that can be stopped or started at will.  Liquid
mixtures, which can be pumped and metered, are ideal for providing
this.  Some typical examples, with their performances, are listed in
Table 3, page 78.

One seldom -mentioned advantage of liquid propellants is that some of
the most powerful combinations (e.g."  kerosene and liquid
oxygen-"lox") are also very cheap, costing only a few cents per pound.
Since large rockets contain hundreds or even thousands of tons of fuel,
this is no trivial matter.

On all counts, therefore-performance, control (including ability to
stop and restart), and economy-liquid propellant mixtures appeared much
superior to solid or powder ones.  For this reason almost all
space-fligbt discussions from the time of Tsiolkovsky onward were based
on liquid propel] ants-usu ally alcohol, or a hydrocarbon, or hydrogen,
burning with oxygen.

Yet technological progress has a curious way of doubling back on
itself.

During World War II, after the liquid propellant rocket had been fully
proved, new types of solid propellant were discovered which greatly
narrowed the "energy gap."  Much more surprising, ways were found of
controlling, stopping, and even restarting solid propellant motors,
which have now been built in sizes (20 feet in diameter!) beyond all
reasonable expectations of a few years ago.  Such giant motors are
valuable as strap-on boosters to provide additional thrust at takeoff;
but it seems unlikely that they will displace the liquid-propellant
systems that have dominated space exploration since the 1940's and
which will do so at least for several decades to come.

Reduced to their simplest elements, these systems -have to comprise the
following items:

1. Fuel tank

Power For Splace 0 51

Combustion

Payload Oxidizer pumpcha .  mber

Fuel tank IJ Oxidizer tank Nozzle

Controls Fuel pump Pump motor

Fig.  4. Liquid-propellant rocket.

2. Oxidizer tank 3. Fuel pump 4. Oxidizer pump 5. Pump motor (s) 6.
Combustion chamber 7. Guidance system 8. Structure.  9. Payload

The first two items had better be defined now to avoid confusion.
Together, fuel and oxidizer make up the propellant; the fuel is what
burns, the oxidizer is what must be mixed with it to support
combitstion.  The commonest fuel is some variety of kerosene, similar
to that burned in jet engines.  The most powerful-and the most
difficult to handle, because of its extremely low temperature-is liquid
hydrogen.  The first large rocket (V-2) used alcohol; chemicals like
aniline and ammonia may also be used as fuels in special
applications.

The oxidizer is usually oxygen itself, in the liquid form; however,
chemicals rich in oxygen are sometimes employed (e.g."  nitric acid,
nitric oxide, hydrogen peroxide).  There is even one "oxidizer" that
contains no oxygen, the hyper reactive element fluorine, which has been
used in some experimental rockets.  Like the detergents that wash
whiter than white, fluorine is an oxidizer that supports combustion
better than oxygen, so well, indeed, that ignition is usually
spontaneous.

It is also possible to combine both fuel and oxidizer in a single
component, giving what is known as a monopropellant.  This considerably
simplifies the design of a rocket, since only one tank and one pump are
then needed.  However, the dangers of such a system are obvious.  With
separate fuel and oxidizer, nothing can happen until they are mixed in
the combustion chamber; barring leaks, the system is fail-safe.  But a
monopropellant is potentially an explosive and could start reacting in
the tank or pipeline before it got to the combustion chamber, with
disastrous results.  Not surprisingly, therefore, mono propellants have
had only limited application.

It will be realized that in the chemical rocket the propellants (i.e."
fuel + oxidizer) serve a dual purpose.  They are the source of energy
of the system, and when ejected after combustion, their momentum
provides the thrust.  One could, in theory, separate these two
functions by burning the propellants but not discarding them, and using
their energy to eject some other material.  This would be an absurdly
inefficient procedure in the case of chemical rockets, but as we shall
see later, it is precisely what happens in the case of the nuclear
rocket, where fuel and propellant fluid are quite separate.

The first time all the items in Figure 4 worked successfully in a
really large rocket was on October 3, 1942, when a V-2 missile rose
from its launching pad at Peenemfinde and plunged into the Baltic 120
miles away.

That evening General Walter Dornberger, who directed all German Army
rocket development, told his colleagues, "Today the spaceship was
born!"  It took nineteen years for the baby to become strong enough to
carry a man.

The story of German rocket research has been well recorded elsewhere
(see

Bibliography) and in any case is outside the scope of this book.
Sufficient to say that, in 1932, officers from the Ordinance Department
witnessed rocket firings by the Verein frir Raumschiffahrt but were
unfavorably impressed both by the vehicles' performances and the aura
of publicity that surrounded them.  As von Braun puts it, "I attempted
to persuade Colonel

Becker that our showmanship was necessary, as a means of relieving our
chronic financial stringency.  Becker, however, was not slow in
pointing out the incompatibility of any and all forms of showmanship
with the development of a long range arm in the Germany of 1932.  He
finally offered us a degree of financial support provided that we were
prepared to do our work in the anonymity assured by the Army..  .." So,
at the ripe age of twenty, Wernher von Braun took charge of
liquid-rocket development for the

German Army, and ten years later the V-2 made its first flight.

Although it has now been completely dwarfed by its successors, this
14-ton rocket was such an advance on anything that had gone before that
many people (notably Churchill's opinionated scientific advisor

Lord Cherwell) refused to credit its existence.  In almost every
department -speed, range, altitude, power-it set new records.  Above
all, it was the first manmade object to reach space, for in vertical
launchings it was able to attain heights of more than 100 miles.

In just over 60 seconds of powered ascent the V-2 burned almost 10 tons
of propellants (alcohol and liquid oxygen), which gave it a speed of
3,800 mph, or more than one mile a second.  This was sufficient for it
to continue coasting as a free projectile for a total distance of 200
miles; after fuel burnout, it was unguided and traveled on a ballistic
trajectory, like a normal artillery shell, taking 5 minutes for its
full flight.

Although it is rather meaningless to talk about the "horsepower" of a
rocket-the only parameter which makes much sense is thrust-the V-2
converted energy at the rate of more than half a million horsepower;
heat equal to that produced by the electric generating plant for a
large city had to be handled in a volume of a few cubic feet.  Cooling
was achieved by allowing the alcohol fuel to circulate through the
double wall of the engine before it entered the combustion chamber.
This idea-re generative cooling-is now almost universally employed and
sounds very simple in theory; but it took thousands of experiments and
hundreds of spectacular explosions, from the time of Goddard onward,
before it was reliably achieved.  If the flow of cooling fluid falters
for a fraction of a second, the ravening heat of the engine will burn a
hole almost instantly through the thin metal of the combustion chamber,
which melts at a temperature thousands of degrees lower than the fires
it contains.

The V-2 consumed fuel at a rate more appropriate to a firefighters'
pump than anything that had hitherto been called an "engine."  The
total propellant flow was 275 pounds per second; to handle liquids at
this rate, and to force them into the combustion chamber against the
pressure of the continuous explosion taking place there, required pumps
driven by a 700-bp motor.  By normal engineering practice, this motor
would have absorbed all the rocket's payload; however, as it had to
operate only for one minute, durability was nota problem.  The tiny
tur

Plate 5. V-2 being prepared for launching at White Sands Proving
Ground.

American Institute of Aeronautics and Astronantics, Inc.

bine developed for this task was driven by superheated steam produced
by the decomposition of hydrogen peroxide.  (The violently reactive
pure chemical, not the feeble 5 per cent solution sold in
drugstores.)

Though the V-2 had four conventional fins, they could affect its flight
only in the lower atmosphere, ar~d their main purpose was to keep the
missile from tumbling when it approached its target.  During powered
ascent, most of the control was provided by small rudders or vanes in
the jet; since they reacted on the exhaust gases themselves, they were
just as effective in space as in the air.

The two sets of rudders (one for lateral, one for vertical control)
were programed by an onboard automatic pilot to follow the required
flight path.

The autopilot used the first application of what is now known as
inertial guidance; except for a few experimental models, the V-2 was
not radio-controlled, which would have made it liable to outside
jamming.  Once it had left its launch pad it was on its own; nothing,
except a direct hit by another missile, could deflect it from its
course.

Inertial guidance is a kind of positional memory; it is the only form
of navigation that does not depend upon external landmarks or
observations.  It allows a man in a moving, completely enclosed box to
tell where he is at any time, provided only that He knows where He
started from.  At first sight this seems impossible, but like many
impossibilities it looks simple when one knows how it is done.

All movement involves acceleration-a positive acceleration on starting,
a negative one on stopping.  Acceleration can be readily measured by
simple instruments; an ordinary spring balance with a weight on it can
be used as an effective "accelerometer."

Imagine such a spring balance, placed on the floor of an elevator
cage.

When the cage is motionless or is moving at a steady speed, the balance
will give its normal reading.  But it will read above normal (too
heavy) when the elevator is starting, below normal (too light) when it
is stopping.  The excess, or deficiency, in weight will be exactly
proportional to the acceleration of the cage.

If one timed these changes with a stopwatch and did a few calculations,
it would be a straightforward task to calculate the speed acquired by
the cage, and hence its position at any moment.  This can be done
instantaneously by a very simple form of computer.  In a highly
inaccurate

56 * THE PROMISE OF SIIACE

mariner, the human brain often performs this same function.  When a man
enters an elevator, the pressure on his feet tells him wlictlicr it is
going up or down, and his time sense allows him to estimate when He is
approaching the desired floor.  And this, in principle, is all there is
to inertial guidance.

In practice, needless to say, there are complications.  An ascending
space vehicle is not like an elevator, constrained to move in a single
direction.

It invariably travels along a curve, and so is subject to accelerations
in all three planes; therefore, it requires not one, but three
accelerometers to detect its motion and compute its velocity.  They
also have to be extremely sensitive, yet able to withstand considerable
shock and vibration.  Reconciling these conflicting requirements has
taxed the art of the instrument maker to the utmost.

I do not know who invented inertial guidance, if indeed any single
person ever did so.  But I can still clearly remember my first
encounter with the principle, when it was enunciated by the late J. H.
Edwards, an eccentric near-genius who was the technical director of the
British Interplanetary

Society immediately before World War II.  Edwards worked out, and
published in the January, 1939, issue of the BIS.  Journal, the
mathematics of such an instrument, which he called an "absolute
accelerometer."  The Society, with wild optimism, even started its
construction, and Edwards proposed that we test it on the escalators of
the London Underground.  (This I should like to have seen.) Little did
any of us imagine that far more ambitious tests of such instruments
were already in progress on the other side of the

North Sea and that many of them would be arriving in London at high
velocity within five years.

Luckily for the Allies, Hitler also failed to foresee the future; he
did not believe in rockets.  He had dreamed that the V-2 would never
cross the

English Channel, so did not give it the support that might have changed
the progress of the war.  For this, both victors and vanquished may
well be thankful.  The first nuclear chain reaction was achieved in the
same month as the first V-2 flight.  If southern England had been
evacuated as a result of rocket bombardment, the invasion of Europe
might never have taken place-and, almost certainly, the atomic bomb
would have been used first against Germany, not Japan.

After the collapse of Germany in the spring of 1945, Dr.  von Braun and
more than a hundred of his top men surrendered to the United States
Army-a few jumps ahead of the advancing Russians.  Stalin, to his
loudly expressed annoyance, secured only a handful of the senior
scientists, but several hundred production engineers and technicians
were "persuaded" to work in the USSR for some years.  Perhaps even more
valuable to the Russians was the capture of the vast underground V-2
plant at Nordhausen, intact apart from one hundred missiles
surreptitiously whisked away by the United States

Army a few hours earlier.  This operation was quite illegal, since

Nordhausen and all its equipment were in the zone already assigned to
the

USSR.  Many Americans have since wished that the Army had compounded
its felony by blowing up the whole plant, instead of leaving it in full
working order for its grateful and incredulous allies.

However, since brains are always more valuable than hardware, the
United

States had much the better bargain; it merely failed to exploit it, for
more than five years.  By then it was the old story of too little and
too late, for the USSR.  had achieved a head start that would take more
than a decade to overcome.

Apart from the tremendous increase in size, from the 14 tons of the V-2
to the awesome 3,000 tons of the Saturn 5, the improvements in rocket
design during the 1950's and 1960's lay more in increased
sophistication and reliability than in major changes of concept.
Engines became more efficient as their combustion-chamber pressures
were raised from less than 300 to about 1,000 pounds per square inch,
with even higher values now in sight.

Fuels of greater energy content than alcohol-e.g."  kerosene and,
finally, liquid hydrogen, the ultimate chemical fuel-were developed.
The airship like fins of the V-2 shrank and, frequently, vanished
altogether from such missiles as Atlas and Titan, which make few
concessions to aerodynamics and are virtually flying cylindrical
storage tanks.  Steering is now effected by pivoting the engine, or
engines-just like the outboard motor on a small boat.  This is a more
complex but more efficient arrangement than the

Goddard V-2 solution of rudders in the jet exhaust.

Not so obvious merely by looking at the designs are improvements in
materials and constructional techniques, which have steadily reduced
the dead, or empty, weight

Plate 6. Cutaway view of Titan 3: a standard liquid-fueled rocket of
the 1960's, able to develop more than 2.5 million pounds of thrust in
its four stages.  American Institute of Aeronautics and Astronautics,
Inc.

of rocket structures.  In the V-2 the propellant tanks were enclosed
inside an outer skin; in later rockets the tanks themselves form the
main body of the vehicle.  The material of which they are built is
sometimes so thin that they may have to be pressurized to prevent them
from collapsing; they are, in effect, metal balloons, capable of
holding a dozen or more times their own weight in fuel and oxidizer.

As a result of all these improvements, the range of single-stage
rockets of the V-2 type rose from 200 miles in 1942 to well over a
1,000 miles by the 1950's.  Though such performances would have
permitted scientific, and even manned, flights some hundreds of miles
into space, they were not adequate for the task of escaping completely
from the Earth.  To understand why this was the case, let us now look
at the obstacles on the road to the planets

ESCAPE FROM EARTH

Any project for leaving the planet Earth has to take account of two
dominant factors-the presence of the atmosphere and the force of
gravity.  They are not independent; if gravity were weaker, the
atmosphere would be less dense, and would also extend farther out into
space, since it would not be held so tightly to the surface.  Such a
situation prevails on Mars, where the gravity is one-third and the air
pressure only one-hundredth of ours.  On the Moon conditions are even
more extreme; the gravity is one-sixth of Earth's, and the atmosphere
has leaked away completely.  (However, this must not be taken as a
general rule; Venus has a slightly weaker gravity than Earth, but her
atmosphere, for unknown reasons, is many times more dense.)

To the would-be space traveler, our atmosphere is both a help and a
hindrance.  On the way out, its resistance cuts back the speed attained
by an ascending spacecraft, and extra fuel has to be carried to
overcome this loss.  The penalty decreases with the increasing size of
the vehicle and is relatively unimportant for very large rockets,
though it dominates the performance of very small ones.

This is a consequence of the well-known square-cube law.  The mass of a
body increases as the cube of its dimensions; its surface area, only as
the square.  Thus larger bodies have proportionately less area, and
therefore less air resistance, than smaller ones.  if a cannonball and
a marble are thrown at the same speed, the cannonball will go much
farther.  It was this effect which, for more than a thousand years,
obscured the true laws of motion.  Fortunately the very mode of
operation of the rocket 60

minimizes the influence of air resistance.  Where the atmosphere is
densest, at ground level, the rocket is moving at its lowest speed.
When it has gained appreciable velocity, the atmosphere is already
thinning rapidly.  And by the time the rocket has reached its maximum
speed, it is in frictionless space.

On the return from space, the atmosphere is almost wholly beneficial;
it acts as a 100-mile-deep cushion, absorbing the enormous velocity of
re-entry.  None of our past feats and future plans for manned space
travel would be possible if we had to do all our braking by rocket
power alone.

Thanks to heat shield and parachute, the final landing on Earth can be
achieved without expenditure of energy.

The question "Where does the atmosphere end?"  is one that cannot be
answered simply-which is rather unfortunate, since it is now a matter
of great legal importance.  According to international law, most
countries claim jurisdiction over vehicles traveling through their
"airspace," whatever that may be.  Attempts to define it now run to a
good many million words.

The atmosphere, in reality if not in law, has no definite end; it
slowly thins out into the near (but not perfect) vacuum of
interplanetary space.

For every 3 miles of altitude, the air density is approximately halved.
Men can live and work without artificial aids at heights of 3 to 4
miles if they are given time to adapt themselves.  But 5 miles marks
the limit of human endurance for sustained periods; Mount Everest (6
miles high) is already beyond that limit.  A man can exist there for
some time without breathing gear, but he cannot exert himself.

Signposts are always helpful on any road, and the list below is an
attempt to establish a few on the road to space.  Their positions are
only approximate and in some cases debatable.  As far as an unprotected
man is concerned, even 10 miles up is already "space"; at the other
extreme, 100 miles is not high enough if one wishes to establish a
satellite in a permanent orbit.

The height at which a satellite, moving at orbital speed of 18,000 mph,
encounters catastrophically increasing atmospheric drag is almost
exactly 100 miles.  For many practical purposes, therefore, this may be
regarded as the beginning of space.  Below this altitude, no pure
spacecraft is capable of prolonged free orbital flight.

TABLE 1

THE EARTH'S ATMOSPHERE

HEIGHT, TEMPERATURE' PRESSURE

MILES DEGREES F.ATMOSPHERESCHARACTERISTICS

0 -100 to +1001Sea level 5 0 to1 004/10Limit of unaiaed human life -1:
2/111Limit with oxygen mask 2: 1/ 1 00Limit for aircraft 0 1/1,000Limit
for ballons 60 -1001/1,000,000Ionosphere 70 +1001/1,000,000,000Meteors
burn up 100 500 to 1,5001/1,000,000,000,000Satellites re-enter; "space"
begins legally?  600 1,000 to 3,00010-mUpper limit of aurora

NOTE: For very high altitudes, the figures shown are merely
rel)resentative; they can vary widely.  Thus, at 600 miles~ the daily
temperature variation can be more than 1,000 degrees!

There are a number of ways, not yet widely exploited, in which the
atmosphere may be used to assist departure from the Earth.  Balloons
have been used as platforms to carry small rockets to great altitudes
before ignition, and there have been many studies of schemes for using
atmospheric oxygen for the early stages of departure.  All these
involve great engineering complications and in most cases appear to be
more trouble than they are worth; but the time may well come when
spacecraft receive a considerable part of their initial boost by jet-
or ramjet-propelled lower stages, capable of flying back to their
launching sites for re-use after each mission.

One of the first facts that scientists discovered when they started
making balloon ascents in the eighteenth century was that it becomes
rapidly colder as one goes upward.  Indeed, this is obvious to anyone
who has ever done any mountaineering.  At great heights, though the Sun
may be shining in the clear sky, it is always extremely cold, and it is
possible to get sunburn and frostbite simultaneously.

It is cold at great altitudes, despite the increased strength of the
unhindered sunlight, because the air is too thin to absorb much heat;
it can thus no longer act as a

Escape Front Earth 0 63

thermal bath, warming all bodies immersed in it.  The temperature
recorded by a thermometer (shielded from the Sun, of course) reaches a
minimum of60 degrees F. at an altitude of about 10 miles; then,
surprisingly, it starts to climb again.  At 30 miles' altitude it has
risen to the freezing point; this zone of relative warmth coincides
with the existence of a layer of ozone, very tenuous but, vital for the
protection of life on Earth, as it blocks the Sun's dangerous
ultraviolet rays.

Thereafter the temperature falls again to a second low, and about 60
miles up it reaches a new minimum of100 degrees F. But now we are
approaching the ionosphere, where incoming solar radiation produces
intense electrical activity.  So the temperature starts to rise again,
very rapidly.  Soon it is hotter than at sea level; 100 miles up (the
frontier of space) the temperature reaches the boiling point and
continues to rise rapidly to 1,000 degrees or beyond.

These facts, which were discovered in the 1930's, were gleefully seized
upon by some critics of space flight to prove that any vehicle would
melt as soon as it left the atmosphere.  I well remember one newspaper
article that had the sensational title "We Are Prisoners of Fire."
Others suggested that shooting rockets into the inferno overhead would
cause it to leak downward and burn up the world.

The explanation of this paradox is that at such extreme altitudes, the
atmosphere is so thin that the word "temperature" no longer has its
conventional meaning.  At ground level the molecules of nitrogen and
oxygen which compose the air are so tightly jammed together that they
travel, on the average, only a few millionths of an inch before they
collide with their neighbors.  The air thus behaves as a continuous
fluid, and a thermometer immersed in it will give a definite reading,
just as it would in a bath of water.

One hundred and fifty miles up, however, the situation is entirely
different.  The molecules have to travel, not millionths of an inch,
but something like one mile before they encounter each other.  Although
their individual velocities may be those that correspond to
temperatures of thousands of degrees, they are so few and far between
that the amount of beat they actually contain is negligible.  A
thermometer immersed in them would give no meaningful reading at all.

A I Ton

1/4 Ton

AIC.t 10 Pounds I Pound Distance from center of Earth' Miles

Fig.  5. Gravity and distance.

A good analogy of this situation is provided by the common "sparkler"
firework.  This gives off showers of incandescent sparks so bright that
their temperatures appear to be several thousands -of degrees.  But
when they fall on the hand, they produce no sensation whatsoever; they
contain so little matter.  that their heat capacity is negligible.  So
it is with the air of.  the ionosphere and beyond.

As far as outgoing spacecraft are concerned, therefore, the atmosphere
ig not very imp(?rtant; it is little more than the scenery along the
road.  But that road, of course, winds uphill all the way, because of
the inescapable influence of gravity.  That is the force which has
-bound us so long to our native planet and which even now taxes out'
skill and resources to the utmost when we attempt to leave it.

Gravity may be one of those fundamental, irreducible entities which has
no "explanation"; it simply is.  Despite immense efforts, scientists
have made little.  progress- in understanding it, and none in modifying
or controlling it.  In the sevctiteenth century Sir Isaac Newton
discovered the law of gravitation, which makes apples fall and keeps
stars in their

Courses, but his great law was a description, no tan explanation.
Though it could predict, with amazing accuracy, the movements of bodies
under the influence of gravity, it said nothing about the iricelianism,
if any, of this universal force.

Almost three hundred years later, Einstein's General Theory of
Relativity introduced some subtle modifications to the Newtonian
picture.  It replaced the idea of a force acting between two bodies
with that of curved space-a concept that only mathematicians can grasp
and which so far has had not the slightest practical application.  For
the purposes of space travel, it is as if the

General Theory had never been formulated; astronauts will always base
their calculations on Newton's law.  Any deviations from it are so tiny
that they will cause about as much concern as does the curvature of the
Earth to an architect when he is planning a house.

Let us, therefore, forget all about theories of gravity and consider
only its effects.  (Later, in Chapter 24, we will see if there is any
chance of neutralizing it in the manner beloved by the early
science-fiction writers.) Like the air itself, gravity is such a
universal phenomenon that we take it for granted and seldom think about
it in the ordinary course of events.  It may dominate the lives of
steeplejacks and mountaineers; we are usually aware of its existence
only when we slip, run upstairs in a hurry, or drop a valuable and
fragile object.

It was Galileo who demonstrated the surprising fact that all objects
fall at the same rate, no matter how much they weigh.  For 2,000 years,
since the time of Aristotle, most thinkers had taken the common-sense
view that the heavier the object, the faster it would fall; DO one
until Galileo had thought of putting the matter to an exact,
quantitative test.  He found that the acceleration produced by gravity
on any unsupported body was 32 feet per second per second (usually
written 32 it.  /sec.2

This means that, starting from rest, a falling object is moving at 32
feet per second (20 mph) after one second; 64 feet per second (40 mph)
after two seconds; 96 feet per second (60 mph) after three seconds; and
so on.  Thus very large velocities can be built up extremely quickly
though near the

Earth's surface, air resistance soon comes into play and limits the
maximum speed attainable.

The value of 32 feet per second per second is usually referred to as I
g, and is almost constant over the whole globe.  (It is a fraction of a
per cent larger at the poles than at the equator.) However, the
acceleration of gravity varies considerably from planet to planet; as
is well known, it is much lower on the Moon, where the value is
approximately one-sixth of

Earth's (i.e."  five feet per second per second).  On some very tiny
moon lets and asteroids, only a few miles in diameter, gravity is so
weak that a falling body would scarcely appear to move.  But on the
giant planet

Jupiter, gravity is about 23"2 times as great as on Earth; a falling
object would gain speed by 50 miles per hour every second!

It is a fact of everyday experience that moving upward against the
force of gravity involves work, and therefore a source of energy must
be available.

A climbing man obtains this energy from the food he has eaten; he would
be doing well if he climbed one mile on one meal.  An ascending rocket
must get the energy it needs for its mission from the fuel and oxidizer
it carries in its tanks.  Mountaineer and rocket thus face similar
problems, but they solve them in very different ways.

A climbing man expends energy at a more or less constant rate and moves
at a fairly uniform speed.  He can also stop at any point and rest,
without falling back and losing any of the altitude that he has
gained.  But a vertically rising rocket cannot do this, since it has no
support; during every second of flight, gravity is inexorably deducting
32 feet per second from its speed.  For this reason spaceships and
mountaineers have to use entirely different strategies to attain their
objectives.

Yet the spaceship has one advantage: the force that it is fighting
diminishes with increasing altitude, according to the inverse-square
law first enunciated by Newton.  For the non mathematically minded,
this simply means that if you double your distance from the Earth's
center, gravity is reduced to a quarter; increase the distance three
times, it is reduced to one-ninth; ten times, to one-hundredth; and so
on.  Thus for small distances the weakening of gravity is very slight,
but at great distances it fades away rapidly.  Though it never becomes
zero, for almost all practical purposes it may be ignored after a few
million miles.

Some actual figures may help to make the picture clearer.  One hundred
miles up-where the closest satellites orbit, just before they re-enter
the atmosphere-gravity still has 99 per cent of its sea-level value.
The average man, standing on bathroom scales at the summit of a
100-mile-bigb mountain, would observe that he had lost about two pounds
of weight, and would not be aware of the difference.  (The astronaut
whizzing past him at 18,000 mph at exactly the same altitude, of
course, feels no weight at all.

The reason for this will be discussed in detail later; for the moment
it is necessary only to note that the mountaineer is supported, while
the astronaut is in free fall.  Anyone who has ever had a chair
suddenly jerked away from underneath him will appreciate the
distinction.)

At an altitude of 1,000 miles-a quarter of the Earth's radius-gravity
is cut to 64 per cent of its sea-level value.  To reduce it to
one-half, it is necessary to climb to 1,700 miles.  These heights are
of course very modest in terms of rocket performances, but they show
why gravity is a constant, invariant factor in our everyday lives.

Figure 5 expresses the same facts in graphical form, with the Earth
drawn to scale.  Note that at the Moon's distance of 240,000 miles the
force of gravity is almost too small to be indicated; nevertheless, it
is still powerful enough to keep the enormous mass of our solitary
natural satellite firmly chained in its orbit.

The steady falling off of gravity with distance from the Earth gives us
a mental picture, or model, from which a great deal can be learned.
Climbing out of the Earth's gravity field is rather like ascending a
slope which is at first very steep but which slowly flattens out until
at last it becomes almost horizontal.  Thus the early stages of the
ascent are extremely difficult and require the expenditure of a great
deal of energy, whereas the final ones require practically no energy at
all.

We can set a precise numerical value to the height of this imaginary
gravitational hill, up which we must climb in order to escape from
the

Earth.  When we calculate the total amount of work which has to be done
to leave our planet completely, we obtain a surprisingly simple and
mathematically beautiful result.  It turns out that lifting a body
right away from the Earth, and out into the depths of space, requires
exactly the same amount of work as lifting it one Earth radius-4,000
miles-against a constant gravity pull equal to that at sea level.  So
if you desire a mental picture of the energy needed to escape from the
Earth, imagine climbing a mountain 4,000 miles high, assuming that
there is no falling off in gravity on the way to the top.
Alternatively, imagine climbing a 4-mile-high mountain 1,000 times: it
comes to exactly the same thing.

To make this mental image more realistic, and more useful, it is best
to turn the mountain upside down-to convert it into a pit or crater.
From the gravitational point

/77 M.0

0 Earth

Fig.  6. The gravitational fields of Earth and Moon.

of view, we dwellers of the Earth's surface are in the position of
people at the bottom of a gigantic funnel, 4,000 miles deep.  To
escape, we have somehow to climb the steeply sloping walls; near the
bottom they are almost vertical, but eventually they flatten out into
an endless plain.  This horizontal plain represents gravitation less
space, across which we can travel for immense distances with very
little expenditure of energy-once we have reached it.

The above calculation is one case of a completely general law, applying
to every body in the universe.  To escape from any star, planet, or
moon demands as much work as moving vertically through the radius of
that body, against a gravity field equal to that at its surface.  Let
us anticipate a little and see what this implies in the case of our
nearest neighbor, the

Moon.

We have already said that its surface gravity is one sixth of Earth's;
its radius is very nearly one-fourth of our planet's.  Hence the work
required to escape from it is only 1/(,x~j, or 1~14th, of that needed
to leave

Earth.  Any lunarians are thus at the bottom of a gravitational crater
a mere 170 miles, not 4,000 miles, deep.  This shows how very much
easier it is to escape from the Moon than from the Earth.

Figure 6 shows these two imaginary gravitational craters (the Moon's is
so small that it has been necessary to exaggerate it).  Remember that
this picture is only a mathematical model, having no more physical
reality than the isobars familiar to millions on the television weather
charts or the contour lines on a map.  But a study of it can give a
very clear impression of the energy requirements for the Earth-Moon
journey, and we shall return to it again when we study this in more
detail.  For implicit in this simple model is the entire theory of
flight from world to world; we can use it to visualize the orbits of
spaceships and space.  probes not only around the

Earth but also, as we shall see later, around the Sun itself.

OTHER ORBITS, OTHER MOONS

During the first decade of the Space Age, the Earth acquired almost a
thousand new moons-some very small and temporary, others weighing many
tons and with lifetimes comparable to that of our natural Moon.
Virtually overnight, what had been one of the most impractical and
theoretical fields of mathematics-celestial mechanics became a branch
of engineering affecting the prestige and destiny of nations.

Celestial mechanics is horribly complex; many pure mathematicians would
also consider it horribly ugly, despite the grandeur of its subject
matter.

Even some of its simplest problems have remained unsolved after
centuries of effort, though answers can always be obtained to any
desired degree of accuracy by brute-force methods using giant
electronic computers.  These machines have revolutionized the subject;
it is not too much to say that space research would be as impossible
without them as without the rocket itself.

Luckily, all the important basic ideas in this area can be grasped
without any knowledge of mathematics at all, by the use of the model
described in the last chapter-the 4,000-mile-deep crater which is the
analogue of the

Earth's gravitational field.  The lower slopes of this model are shown
in

Figure 7; if we imagine that it is made of some smooth, hard material
such as perfectly frictionless glass, we can use it to demonstrate the
movements of space vehicles in the neighborhood of the Earth.  All that
we have to do to reproduce them for any initial conditions of velocity
and direction is to see what happens to an 70

(d)

(h)

----------(C) -1,500

-1,000 4,006 miles (b)

Earth (a) ---..--- (e)Lo

Fig.  7. Orbits in the Earth's gravitational crater.

object when it is projected along the slope, like a marble flicked
inside a wineglass.

The case of a vertical launching is the simplest; obviously, the
greater the initial speed, the higher the object will rise before
gravity reduces its velocity to zero.  Then it will fall back, gaining
speed, until it returns to the starting point-at its initial
velocity.

Although this example may seem rather trivial, we can learn several
very important points from it.  The first is that velocity can never be
lost in space; it can be exchanged for altitude, but it can always be
exchanged back again.  In general, no matter what path or orbit a body
takes around a planet, when it comes back to the same altitude (or
distance) it will always be moving at the same speed (though not
necessarily in the same direction; in this case the speed has been
reversed, but the energy is the same).

It is also clear that as the velocity of projection increases, the
altitude reached increases even more rapidly because of the steadily
flattening slope.  Figure 7 shows, to scale, the heights reached by
bodies launched away from the Earth at speeds of (a) 5,000, (b) 10,000,
and (c) 15,000 mph.

It is obvious that as the speed of projection increases still further,
there will be a certain critical velocity at which the body will never
fall back.  Though it will lose most of its initial speed during the
ascent, it will still have some velocity left when it reaches the "rim"
of the crater, and so it will continue to move on outward forever.  The
speed that is just sufficient to climb out of a gravitational field is
known as the velocity of escape; for the Earth its value is about
25,000 mph, or 7 miles per second.

If a body starts off with more than this critical speed, it will still
have something in hand when it leaves the gravitational pit.  However,
the excess velocity cannot be obtained by simple subtraction, because
we are really dealing with energies, not merely velocities.  A body
starting from the bottom of the crater at a speed of 7 miles per second
reaches the top at zero velocity; but one beginning at 8 mps emerges at
considerably more than the one mps that might be expected.  The rather
curious results that follow are shown in this table:

INITIAL VELOCITY, MPS FINAL VELOCITY, MPS

7 051/2 This matter is not very important as far as the present
argument is concerned, but in the case of actual missions it has a
great effect on fuel requirements and flight times (see Chapter 7).

Now consider the case of a body projected not vertically up the
gravitational slope, but horizontally-at right angles to it.  If its
speed is adjusted properly, it can remain orbiting at a constant
altitude, like a motorcyclist in the "Wall of Death" popular in circus
sideshows.  (Though this analogy is a good one, it is not quite
accurate, because friction operates here, and the rider has to keep his
engine running to counteract it.)

This is the now-familiar case of a satellite in a circular orbit, at a
constant distance from the Earth.  It is obvious that the higher the
satellite, the more slowly it needs to move to preserve its position. A
very close satellite requires an orbital speed of 18,000 mph (5 mps),
whereas a distant one like the Moon need move at only about 3,600 mph
(1 mps).

It also follows that as altitude or distance increases, the time to
complete one orbit increases at an even greater rate, for not only is
there more distance to be covered, but the speed in orbit is less. This
fact is expressed in Kepler's famous third law-"the square of the time
for one revolution increases as the cube of the radius"-which was the
clue that led

Newton to his law of gravitation.

We have by no means exhausted the possibilities of our model, for let
us now consider the case of an object projected along its surface at
some arbitrary speed or inclination.  If it does not have enough
velocity to maintain itself at the height where it enters into the
system, it will drop down the slope, but as it does so it will gain
speed, like any falling body.  When it has reached its lowest point-and
its greatest velocity-it will start to rise again, continually
retracing the same inclined curve.

This, of course, is the analogue of a satellite in an elliptical
orbit.

In Figure 8 the elliptical orbit has been drawn so that it touches two
circular ones; it can lie anywhere, but this has been done to
illustrate another idea-transfer from one orbit to another.  It will be
realized that at the upper point of contact, an object in the
elliptical orbit is moving more slowly than one in the circular orbit
here; this is why it falls back to the lower level again.  If it is to
remain in the higher orbit-make a rendezvous-it must be given an
additional impulse.

Conversely, at the lower point of contact the body in the transfer
orbit is moving too fast for a rendezvous, it must therefore receive an
impulse to slow it down if its orbit is to be "circularized."

Before we leave, for the moment, this highly instructive model, there
is just one more case to be considered, that of a body entering the
gravitational field from a great distance and at a considerable
speed.

This is the exact reverse of the "escape-velocity" case; the object
will gain speed as it slides down the wall of the crater.  It will gain
so much, in fact, that it will whip completely around the bottom of the
crater and rise out of it, to disappear once more toward
infinity-eventually regaining all its original speed, though it will be
heading in some different direction.

There are fun-fair operators, doubtless unversed in celestial
mechanics, who have learned to profit by this example.  They display
attractive vases, which can be won

--------(b)

(b) (a)

Fig.  8. Orbits around the Earth: (a) circular, (b) elliptical, (c)
parabolic.

by anybody who can toss a ball into them.  It looks easy, because the
openings of the vessels are quite wide; but the trick is almost
impossible, because any ball that does get into the smooth interior
promptly emerges again with barely diminished speed.  The astronomical
analogue, of which there are several examples every year, is the comet
which enters the solar system from the depths of space, does a hairpin
turn around the Sun, and then beads out once more toward the stars.

A careful study of the perhaps rather unlikely model in Figure 8 will,
therefore, give a very good idea of all the possible trajectories and
orbits of a space probe or satellite moving in the gravitational field
of the Earth.  More than that, it may be generalized for all celestial
bodies-the Moon, the Sun, or any of the planets.  Only the numerical
values are different; thus, for the Moon, escape velocity is only 1%
miles per second (compared with 7 mps for Earth).  For the Sun, however
it is an enormous 400 miles per second; some idea of the forces raging
there can be gathered from the fact that solar eruptions frequently
exceed this speed, so that matter is continually escaping from the Sun.
It must be remembered that Figure 8 is a model, nota map; it shows the
characteristics of possible orbits, not their actual shapes in space.

It will be seen that there are two possible classes of orbits, closed
and open.  The closed ones are circles and ellipses; they repeat
themselves indefinitely.  All real orbits are in fact ellipses; the
circle is the theoretical, limiting case of the ellipse with zero
eccentricity-a state of perfection which does not exist in nature,
though it has been approached by some artificial satellites.  Venus has
the most perfectly circular orbit, with an eccentricity of 0.0068.  A
synchronous satellite like Early Bird has an orbital eccentricity of
only 0.0005-ten times better.

The open orbits, which never repeat themselves but lead off to
infinity, are hyperbolas or parabolas.  Like the circle, the parabola
is a limiting case which exists only in theory.  It is the orbit of a
body which has exactly enough velocity to escape-not one micron per
millennium more or less.  So in practice, all escape orbits are really
hyperbolas.

The Greek mathematicians, in the fourth century B.C."  discovered that
all these curves can be obtained by cutting a slice through a cone.  If
the slice is parallel to the base, the result is a circle; as the
section is tilted, the resulting curve becomes first an ellipse, than a
parabola, then a hyperbola.  So the Greeks called them all "come
sections" and worked out their mathematical properties from a pure
sense of aesthetics.

Two thousand years later, Kepler found that the ellipse is the path in
which all the planets travel around the Sun.  This caused great dismay
to the classical scholars, who believed that anything as celestial as a
heavenly body must move along the only "perfect" curve, the circle.

One can hardly imagine what they would have thought, could they have
known that the time was coming when the come sections would lead man
himself into the heavens.

THE PRICE OF SPEED

We have seen in the last chapter that the speed required for even the
simplest and easiest space mission-orbiting the Earth-is about 5 miles
a second, or 18,000 miles an hour.  To escape completely requires 7
miles a second (25,000 mph), but once this critical speed is attained,
a whole range of possibilities opens up, as shown by the table on page
77.

Ignoring for the present the rather odd fact that it is twice as
difficult (in terms of velocity) to reach the Sun as the nearest star,
this shows that a very slight extra speed over the minimal escape
velocity brings the closer planets within range, as has already been
demonstrated by the various Mars and Venus probes.

Tsiolkovsky used the phrase "first cosmic speed" for the orbital
velocity of 5 mps, and "second cosmic speed" for the escape velocity of
7 mps; these expressions are still employed in contemporary Russian
space writings.  Even the lower velocity seemed so wildly beyond hope
of attainment at a time when airplanes could barely reach 100 mph that
one can hardly blame the early critics of astronautics for their
skepticism.

And yet Tsiolkovsky and his successors had shown in complete
theoretical detail how such speeds might be attained by means of
rockets, provided that certain engineering problems could be overcome.
It was all a question of getting a sufficiently high exhaust velocity
and an efficient enough structure.  These were the two vital factors;
everything else was secondary.

TABLE 2

MISSION LAUNCH SPEEDS

LAUNCH SPEED

MISSION MPHMILES/SEC.

Close Earth orbit 18,0005

Voyage to Mars or Venus 26,0007

Voyage to Jupiter 32,0009

Voyage to Pluto 35,00010

Voyage to nearest star 37,00010

Voyage to Sun 70,00020

Let us go back to the brick-carrying sled used in Chapter 3 to
demonstrate the rocket principle, and consider how its performance-
that is, its final velocity after all its "propellant" has been
expended-depends on these two parameters.

Common sense, without any mathematical aids, tells us that the final
velocity will be directly proportional to the speed of ejection of the
bricks.  If the bricks are thrown out at 20 mph and the sled reaches a
final speed of I mph, then it will reach 2 mph if the ejection speed is
increased to 40 mph, assuming exactly the same number of bricks are
thrown out as before.

Thus the exhaust speed of a rocket is its most important
characteristic, for its final speed, at "all burnt," is directionally
proportional to this.

Table 3 gives some values for a few representative propellants.

When these figures are compared with the mission requirements shown in
Table 2, it will be seen at once that the old-style powder rocket is
pitiably inadequate.

But even the modern, liquid-propellant rockets have exhaust speeds
which are only a fraction of the "first cosmic velocity."  To perform
any space mission, therefore, we must build rockets capable of
traveling several times as fast as their exhaust speed.

At first sight, it may seem impossible for a rocket to attain a speed
greater than that of the jet that propels it; I have known able
mathematicians who intuitively dismissed the idea.  But it must be
remembered that the jet exhaust always leaves the rocket at the same
speed, whatever the velocity of the rocket itself may be relative to
some arbitrary external point.  As long as there is any fuel aboard,
the jet will continue to give the same thrust, and the rocket will
continue to accelerate.

TABLE 3

ROCKET PROPELLANTS

PROPELLANT EXHAUST VELOCITY, MPH

Black powder (firework) 700

Modern solid propellant 3,000 to 5,500

Alcohol-oxygen (V-2) 6,200

Kerosene-oxygen (Atlas, Saturn)6,500*

Hydrogen-oxygen (Centaur, Saturn)8,500

Hydrogen-fluorine 9,000.

Hydrogen (nuclear rocket) 20,000 and up

Ions (electric rocket) 40,000 and up

Sea-level values.  Exhaust velocities in vacuum could be 10 to 15 per
cent higher.

To return to the analogy of the sled and its load of bricks, each brick
gives the same impetus to the vehicle, whether the sled is standing
still or moving at 100 miles an hour across the ice.  Since the fuel is
carried along with the vehicle and shares its speed at any time, the
sled's velocity cannot affect its performance.

The fact that rocket exhaust speeds are considerably less than those
needed for space missions does not, therefore, make them impossible; it
merely makes them difficult.  We can see how difficult if we look again
at the man on the sled and ask ourselves what amount of propellant be
would have to throw off in order for his vehicle to reach "exhaust
speed," that is, the speed with which he is throwing out the bricks.

It is easy to see what the minimum weight must be.  If all the
propellant could be ejected simultaneously, in one explosive effort,
and if its weight equaled that of the empty sled, then the velocities
would also be matched.

After the Big Bang, we would have two equal masses moving in opposite
directions, with equal speeds [Figure 9 (a)].

In this case, the initial mass of the system (vehicle plus propellant)
would be twice that of the empty, or final, mass.  It would be said to
have a "mass ratio" of 2. Such a ratio presents no engineering
difficulties, though it is a good deal higher than usual for surface
vehicles; the average automobile has a mass ratio of about 1.03, since
only about 3 per cent of its weight is fuel.  It is attained by some
aircraft, which can carry their own empty weight in fuel.

30 V

M M

=-V =-V

M 1.72 M

Fig.  9. The rocket-velocity law.

However, the explosive, or "instant-burning," case we have described is
not applicable to the rocket, where combustion takes place over a
period of time which may last for several minutes.  And certainly the
man on the sled would require a considerable time to throw out a mass
of bricks more than equal to his own weight!

This alters the situation a good deal, reducing the efficiency of the
system.  Because all the propellant is not ejected at once, work has to
be done to accelerate the unused material, up to the moment until it is
finally discarded.  This means that more propellant has to be
carried-and more propellant has to be carried to accelerate that, in an
infinite but fortunately diminishing series.  The very last brick on
the sled has to be carried to the bitter end; when it is finally
jettisoned, it has almost reached the velocity of the payload; yet all
the work done to accelerate it to that point is a complete waste,
though an unavoidable one.

It is straightforward, though tedious, to calculate the additional mass
of bricks now needed to bring the vehicle up to "exhaust speed" without
using any higher mathematics.  (Anyone who likes to try may assume that
the propellant mass is split into first 1, then 2, then 4, 8, 16, etc."
bricks.

As the individual units get smaller and smaller, he will see that the
answer converges to a limiting value.) In the case of a real rocket,
where there is a continuous flow of material, the calculus has to be
used, and it can be easily shown that in order for the vehicle to reach
the speed of its exhaust, the mass ratio must be increased from 2 to
the somewhat higher value of 2.72.  Thus the vehicle has to eject 1.72
times its empty weight of propellant [Figure 9 (b) 1. The 0.72 is the
penalty we have to pay for carrying along part of the fuel until it is
needed; it might be much worse.

The now-primitive V-2, it is interesting to note, had a mass ratio
considerably higher than 2.72.  Its loaded weight was 28,000 pounds,
its empty weight 8,500 pounds, and the ratio of these two figures is
3.3. In theory, therefore, a V-2 could travel faster than its exhaust
(5,000 mph); that it actually achieved only 3,600 mph was due to air
resistance and gravity losses.  It could have attained its theoretical
performance in the vacuum of space.

Now let us be more ambitious.  What load of bricks has the sled to
carry, if its final speed is to equal twice that of its "exhaust"?

It turns out that we have to square the mass ratio, thus increasing it
from 2.72 to 2.722, or 7.4. In other words, the sled has to carry 6.4
times its own empty weight in propellant.

Similarly, for three times the exhaust speed, the mass ratio has to be
cubed, giving a value of almost exactly twenty, and so on.  There is no
theoretical limit to the process, but clearly the practical
difficulties are increasing very rapidly.  Is it possible to construct
a vehicle strong enough to stand the accelerations of flight whose
empty weight-including payload!-is only one-twentieth of its weight
when loaded with propellants?

But this is what has to be done if we are to build a rocket which can
fly three times as fast as its own exhaust.

These results are shown in diagrammatic form in Figure 10.  In each
case the empty weight of the rocket is assumed to be the same-say, one
ton.  That one ton, remember, must cover the weight of the propellant
tanks, the rocket engine, the control system, the payload-everything.

The old V-2, as we have seen, is slightly better than case (a). Today's
best liquid-propelled rockets can surpass (b), and there are some
solid-propellant rockets that can even match case (c).  The makers
claim that their mass ratio of twenty beats that of nature's most
efficient container, the egg.  However, this figure applies to the
rocket motor only, and the complete vehicle would bring us back to
something poorer than case (b) again.  We can conclude, therefore, that
it is not practical to build a rocket with a final speed more than
twice that of its exhaust.  (There may be exceptions for vehicles built
to operate

The Price 0/ Speed 0 81

(C)

Rocket reaches 3 times exhaust speed (b)

Rocket reaches 2 times Empty exhaust speed weight

(a) Rocket reaches exhaust speed Fuel

Empty weight M19 weight 1

Empty weigh Fuel6.4 weight

Fuel we'ightA1.72 a

Mass ratio: 2.72 7.420

Fig.  10.  Rocket mass ratios..  exclusively in space, where very light
structural materials and novel techniques can be employed.)

The greatest exhaust speed for conventional propellants, listed in
Table 3, is 8,500 mph.  Since orbital velocity is 18,000 mph, it
appears impossible to build a rocket, using hydrogen and oxygen, to
become a satellite of

Earth.

The way out of the dilemma is the simple, effective, but expensive
device of the step, or multistage, rocket.  All the calculations given
above refer to single-stage rockets, where the structure, dead weight,
etc."  which begin a mission are used right through to the end.  But it
is obvious that if we make the payload of our rocket another complete
rocket, which starts to operate only when the first stage has exhausted
its fuel and has been dropped off, we can achieve a much higher final
speed.  In fact, if the two rockets have the same propellants and the
same mass ratio and are identical except in size, the final speed will
be doubled.

How the step rocket works (and why it is expensive) is shown in Figure
11.

Let us suppose that one can design a rocket with a weight breakdown of
80 per cent propellant, 15 per cent structure, and 5 per cent payload,
as shown in Figure 11

80%

Propellant Structure Payload

(b) 80%::15%:

Propellant 2nd stage Structure ~ Payload

Fig.  11.  Weight breakdowns of one- and two-stage rockets.

(a).  (It is possible to do a good deal better than this, but these
values have been chosen to give round numbers.) This being a
single-stage rocket, its 5-per-cent payload might be able to attain a
theoretical final speed of 10,000 mph.  In practice, air resistance and
gravity could reduce this to about 8,000 mph.  Even if the whole of the
payload were replaced by propellant, the mass ratio would show only a
slight improvement-in this case, from 5 to 6.7. The resulting increase
in speed-at the cost of zero payload!  would only be 2,000 mph.

If, however, we take the payload and make it a second rocket, with the
same weight breakdown as the first [Figure 11 (b) 1, then this stage
will have the same performance.  But it would start where the first had
left off, both in velocity and in altitude.  It could add another 8,000
mph to the speed it already possessed, giving a grand total of 16,000
mph.

In actual practice it Would do a good deal better than this.  Since the
second stage would not begin firing until it was scores of miles above
the ground, it would lose very little velocity through air resistance,
and its engine would operate at maximum efficiency.  Moreover, it would
no longer be ascending vertically; it would have started to curve over
toward the horizontal.  This r~cans that gravity drag (which acts in
the downward direction) would be less effective in reducing its
speed.

For all these reasons, the second stage would approach its theoretical
performance of 10,000 mnh, so that its payload would achieve 18,000
mph, or orbital velocity.

The reason why a step rocket can travel so much faster than a
single-stage rocket, whatever its size, is not hard to see.  In a
single-stage rocket, as the propellants become used up we have the
situation where a now unnecessarily powerful, and therefore excessively
heavy, engine is trying to accelerate a lot of useless dead weight. The
big propellant tanks, for example, still have to be carried along even
when they are virtually empty, so that in a sense the overall
efficiency of a rocket steadily decreases as its propellants are
consumed.  In the last seconds of firing time the engine is wasting
most of its effort imparting velocity to structural mass which is no
longer serving any useful purpose.  The only way to improve the
situation is to throw away the empty rocket and to start again with a
new, scaled-down one.

There is no limit to the number of stages that may be employed in a
step rocket or, therefore, to the speed which may be attained by the
final.  stage when the earlier ones have been discarded.  The practical
disadvantage of the step principle, of course, is that after two or
three stages the ultimate payload is an extremely small fraction of the
initial takeoff weight.  In Figure 11 the payload of the single-stage
rocket is 5 per cent, but that of the two-stage rocket is only 5 per
cent of 5 per cent, or a mere 34' per cent.  For multistage vehicles,
such as the Saturn 5 designed for the lunar mission, the percentage of
payload is even less; but that is the penalty that has to be paid for
achieving high velocities.

It is sometimes asked, "Why do we need such high speeds for space
flight?

Could nota rocket leave the Earth at a fairly low, steady velocity,
running its engines at some modest thrust level, rather than going
all-out to reach the escape velocity of 25,000 mph as quickly as
possible?"

Yes, it could-if it had a virtually infinite source of energy.  The
slower the rate of climb in the Earth's gravitational field, the more
wasteful is the expenditure of fuel.  This will be obvious if we look
at two extreme cases.

Suppose the rocket burns all its fuel instantly, so that it acquires
escape speed while it is still at ground level.  (We know, of course,
that air resistance, as well as engineering factors, would make this
impossible in practice.  But there are some anti-ballistic-missile
missiles-ABM's-that do have incredible accelerations even in the lower
atmosphere and will serve to illustrate the principle.)

In this theoretical case, none of the fuel has to be lifted against the
earth's gravitational field; it therefore imparts all its energy to the
rocket and wastes none lifting itself.  It all stays near the
ground-but the rocket escapes from the Earth.  We are, virtually,
dealing with the case of a gun launched vehicle, and the propellant is
used at maximum efficiency.  To look at it in another way, because the
whole process of reaching escape speed takes zero time, gravity which
normally reduces the speed of any vertically climbing missile by 20 mph
every second-has no time to act.

Now consider the other extreme, the case of a rocket which takes off so
slowly that it merely hovers at a fixed altitude.  It burns its entire
load of propellant merely balancing itself against gravity, and gets
nowhere

Clearly, the nearer we can get to the first case, the more efficient
the operation and the smaller the total amount of propellant needed.
Escaping from Earth is difficult enough as it is, without.  aggravating
the problem by making unnecessary concessions to gravity.  We have to
climb out of the gravitational crater as quickly as possible; the more
time we spend lingering on its lower slopes, the more we shall slip
back toward the bottom.

The above argument also throws light on a fallacy often advanced by
critics of space flight in the early days; sometimes trained
mathematicians, who should have known better, fell headlong into the
trap.  Here is a splendid specimen from a speech by one Professor
Bickerton, delivered to the British

Association for the Advancement of Science in 1926:

This foolish idea of shooting at the moon is an example of the absurd
length to which vicious specialisation will carry scientists working in
thought-tight compartments.  Let us critically examine the proposal.
For a projectile entirely to escape the gravitation of the earth, it
needs a velocity of 7 miles a second.  The thermal energy of a gram at
this speed is 15,180 calories..  .. The energy of our most violent
explosive-nitroglycerine-is less than 1,500 calories per gram.
Consequently, even had the explosive nothing to carry, it has only
one-tenth of the energy necessary to escape the earth .. .. Hence the
proposition appears basically impossible ..

General Dornberger has given a vivid eyewitness account of this
happening at Peenernfinde; see The Coming of the Space Age (Meredith
Press), 1967.

The Price 0/ Speed e 85

In this relatively short passage Professor Bickerton managed to
compress two major errors.  One would have thought it obvious that an
explosive was the last substance suitable for a rocket propellant; in
any event, nitroglycerin contains considerably less energy than equal
weights of typical propellants like kerosene and liquid oxygen.  This
fact of elementary chemistry had been carefully pointed out years
before by

Tsiolkovsky and Goddard.

Bickerton's second error is the "energy fallacy" in its purest form.
What does it matter if the nitroglycerin (or other propellant) contains
only a fraction of the energy necessary to lift itself away from the
Earth?  It never has to do so.

What it has to do is to impart that energy to a suitable payload, and
(if it were not for air resistance) that could all be done at ground
level.

Thus even Bickerton's own argument merely proves that at least ten
pounds of nitroglycerin would be required to send one pound to the
Moon.  For actual space vehicles, most of the propellant is burned
within a hundred miles of Earth, and so lifts itself only a fraction of
the way out of the

Earth's gravitational field.  When Luna 2 impacted on the Moon just
thirty three years after Professor Bickerton proved it was impossible,
its several hundred tons of kerosene and liquid oxygen never got very
far from the

Soviet Union-but the half-ton payload reached the Mare Imbrium.

The passage I have quoted is also worth studying for another reason. It
demonstrates how men who should be scientifically trained can let
prejudices and preconceived beliefs distort their logic, so that they
commit almost childish errors when attempting to prove their points.
Space flight, and aviation before it, attracted a lot of this nonsense;
and even today, as we shall see in Chapter 27, there are circles in
which it is a popular pastime to "prove" that though interplanetary
flight is perfectly feasible, we shall never, never be able to reach
the stars.

H. A R 0 UND THE' EAR TH

MOONRISE IN THE WEST

The use of rockets for high-altitude research-the dream which Goddard
had pursued but had never realized in his own lifetime-began
immediately after

World War II.  Many of the V-2's captured by the United States Army
were launched from the White Sands Proving Ground, New Mexico, with
their warheads replaced by instruments which would radio their
observations back to ground stations.  In addition, smaller rockets,
such as the Aerobee and the Viking, were developed purely for
scientific purposes.

This work was very modestly funded and would probably have led to the
achievement of manned space travel around the middle of the
twenty-first century.  Fortunately or unfortunately, depending upon
one's point of view, the main impetus for rocket development was being
provided not by man's quest for knowledge but by his instinct for
survival.  As in the case of the

V-2, the military were quietly providing the real money.

Although the United States possessed, in the Peenemimde team, the most
experienced rocket designers in the world, it showed no inclination to
use them.  Its monopoly of the atom bomb (confidently expected to last
for many years) and its fleet of B-29 Superfortresses made such
futuristic weapons as long-range ballistic missiles appear unnecessary.
Moreover, theoretical studies showed that it would require rockets
weighing several hundred tons to deliver nuclear warheads over useful
distances.  No competent engineer doubted that such vehicles could
eventually be developed, but the cost would be enormous and there
seemed no justification for a high-priority program.

The Soviet Union-and specifically Joseph Stalinthought otherwise.  From
their point of view, intercontinental missiles made excellent sense.
They also had a long tradition of interest in rockets, going back to

Tsiolkovsky, and until the mid-1930's their engineers had probably led
the world in this field-though this fact was not generally known or
believed outside the Soviet Union.

In addition, they had now acquired the priceless background of German
wartime research, a great deal of hardware (including Peenemimde and a
complete V-72 factory), the very few top-ranking scientists and
engineers who had not thrown in their lot with Dr.  von Braun's team,
and more than a thousand technicians.  This was a prize of no small
value, but to imagine that it was responsible for establishing the
Soviet lead in space is absurd.  The United States had the better
bargain, as Stalin was quick to point out.  According to one eyewitness
(Tokaty), he berated General Serov as follows: "This is absolutely
intolerable.... We occupied Peenemiinde, but the Americans got the
rocket engineers.... How and why was this allowed to happen?"

Although a carrier for their first, heavy atom bombs would have to
weigh several hundred tons, the Soviet Union decided to go ahead and
develop it.

When perfected in the late 1950's, it was also large enough to launch
heavy satellites-and to carry the first man into space.  Whether this
had been planned from the beginning, or whether it was a lucky bonus,
is perhaps one of those questions which even the Soviets themselves
cannot now answer.

When it was finally revealed to the outside world at the Paris Air Show
in the spring of 1967 (ten years after its first historic flights), the
giant

Sputnik carrier (Plate 7) proved to be of a highly original design,
bearing scarcely any resemblance to the V-2 formula.  Dr.  von Braun
had already forecast this when he stated that "There is every evidence
to believe that [German engineers'] contribution to the Russain space
program was almost negligible.  They were called upon to write reports
... they were squeezed out like lemons, so to speak.  In the end they
went home without even being informed about what went on in the
classified Russian projects."

The American long-range rocket program remained in limbo until about
1950, though well over one billion dollars was spent on the development
of jet-propelled guided missiles such as Navaho and Snark, which were
no more than robot airplanes capable of cruising only at relatively low
speeds inside the atmosphere.  All were abandoned after the ICBM
breakthrough.

The two events which suddenly revived American interest in long-range
rockets were the outbreak of the Korean War in 1950 and the realization
that thermonuclear (or fusion) weapons could soon be built.  These
would not only be hundreds of times more powerful than the first fision
bombs, but also lighter; they could be delivered by vehicles weighing
about a hundred tons, instead of several hundred.  And so, after
several false starts, were initiated the programs which led first to
ballistic missiles of intermediate range such as Redstone, Jupiter, and
Thor, and later to the true intercontinental missiles Atlas and
Titan.

All this was going on during the period 1950-55, and meanwhile the
scientists were also getting involved.  Many of the younger ones had
been using sounding rockets to explore the upper atmosphere and had
pioneered new fields of research in meteorology, astronomy, and
geophysics.  But this work was as frustrating as it was exciting, for
sounding rockets could spend only a few minutes reporting from space
before they fell back into the atmosphere.  The obvious answer was the
artificial satellite, which could stay aloft indefintely, behaving, as
one wit put it, like a

Long-playing Rocket.

There was much discussion, therefore, of scientific satellites around
1950; as early as 1951, the British Interplanetary Society sponsored a
congress in London on "The Artificial Satellite."  By an accident of
history, all these studies (some of which went into great technical
detail) appeared just at the time when the scientific community was
planning the greatest global research effort ever conceived-the
international Geophysical Year (1957-1958).

The United States committee of the ICY, under the chairmanship of Dr.

Joseph Kaplan, recommended that a satellite be launched as part of the,
nation's program; the suggestion was approved by the government, and
the

White House made the announcement to a somewhat startled world on July
29, 1955.  Little notice had been paid to the statement on April 15,
1955, in the Soviet

Plate 7. The giant Sputnik-carrying rocket displayed at the Paris Air

Show, 1967.  Rolls-Royce, Derby, U.K.

press that an Interdepartmental Commission on Interplanetary
Communications had been set up to develop satellites for meteorological
purposes, so when the USSR.  repeated this item the day after the
American announcement, it was received with amused skepticism.

Then followed the tragicomedy which has been the subject of millions of
words of excuse, apology, accusation, recrimination, and 20:20
hindsight.

Having resolved to orbit a satellite, the United States next had to
decide oil the launch vehicle.

There were three principal candidates.  The Army proposed the Redstone,
being developed at Huntsville, Alabama, by the von Braun team.  Using
this as a first stage, and mounting clusters of solid rockets on top of
it, small payloads could be launched into orbit by the beginning of
1957.  This scheme had the great advantage of using hardware that
already existed, and so could be ready in the shortest time.

The Air Force wanted to use the still-to-be-tested Atlas as the
first-stage booster; this would put a much larger payload into orbit,
as was later amply proved by Project Mercury.  However, it was
practically certain that Atlas would not be ready in time for the IGY,
unless there was interference with its overriding military priority.
(Its first successful flight did not in fact take place until December
17,1957.)

The Navy proposed to develop what was almost a new vehicle, though its
first stage would be based to some extent on the successful
Viking-research rocket, which had now carried substantial payloads to
heights of up to 158 miles.  One of the arguments in favor of this
approach was that the whole project could then be an unclassified,
civilian one, using no military hardware-in keeping with the peaceful,
scientific nature of the IGY.

To decide between these conflicting proposals, a committee was set up
under the chairmanship of Dr.  Homer Stewart; to the bitter
disappointment of the

Army, it selected the Navy's project, which was given the unhappy
name

Vanguard.  The reasons for this decision were as much political as
scientific (if not more so), and the "Stewart Committee" has since been
widely criticized for its verdict.  This is particularly bad luck for
Dr.

Stewart himself, as he submitted a minority report in favor of the
Army's

Redstone project.

The Office of Naval Research, given the go-ahead, started to design the
complex and sophisticated Vanguard vehicle, most of which was built by
the

Martin Company of Baltimore.  Work proceeded on an unrealistically low
budget, with no priority; more important rockets had the first call on
men and materials.  Yet the final outcome was a highly successful
launch vehicle, which made great contributions to space technology; it
should not be forgotten that the longest-lived of all satellites, which
would be in orbit a thousand years hence, apart from the near certainty
that it will soon be collected for the Smithsonian Aerospace Museum, is
the little three-pound Vanguard 1, launched March 17, 1958.  And
Vanguard 3 (September 18, 1959) far exceeded the originally designed
payload, taking 50 pounds of instruments to a high point of more than
2,000 miles.  But by that time no one took much notice, for a week
earlier the Soviets had hit the Moon.

This was merely one episode in a national humiliation that had begun
on

October 4, 1957, when to the utter astonishment of the world the USSR. 
did exactly what it had said it was going to do, and orbited the first
artificial satellite of Earth.  It was at once obvious that a
full-sized

ICBM vehicle-nota small, purely scientific rocket-had been used as a
launcher.  Radar and optical observations showed that though the
announced payload was .184 pounds, the empty final stage also circling
the Earth must weigh several tons; when the even larger Sputnik 2 went
into orbit carrying the dog Laika on November 3, 1957, photographs
obtained by powerful tracking cameras proved that the combined
structure of payload and final stage was more than 60 feet long.

Fortunately for the United States, the Redstone team had refused to
accept permanent exclusion from space.  Dr.  von Braun had made
repeated attempts to get author

Moonrise lit The West0%

ization for his project, and though they were all turned down, be
continued the struggle.  On one occasion he was preparing to launch a
slightly clandestine satellite with a Jupiter-C (virtually a duplicate
of the vehicle which eventually orbited the first United States
satellite, Explorer 1), but the Department of Defense discovered the
project in time to frustrate it.

Not until the first Vanguard test vehicle had exploded spectacularly on
the pad (December 6, 1957) was the Army given permission to go ahead.
On

January 31, 1958, the United States had its first satellite in orbit
and could obtain some consolation from the fact that it had made the
most important discovery of the IGY.  For it was Explorer I that
detected the wide-ranging, invisible halo of the Van Allen radiation
belt.

So, in circumstances more dramatic than any novelist could have
contrived or any scientist would have desired, Earth's new moons came
into being.

Millions of people were to see Sputnik 2, still catching the sunlight
on the edge of space, gliding slowly from west to east across the
ancient constellations.  Few could have remained unmoved by the
knowledge that they belonged to the first generation to set its sign
among the stars.

The uses-scientific and otherwise-of artificial earth satellites will
be discussed in the next two chapters, but before some of these can be
fully appreciated it may be well to look a little more closely at the
orbits they must follow.  These are the expression of nature's traffic
laws; we violate them at our peril.

The critical speed of 5 miles a second, necessary to establish an
orbit, is quite independent of the size or mass of the satellite
concerned; it applies equally to the 100-ton-payload of Saturn 5 and
the barely visible wire hairs launched by the millions in the notorious
"Needles" experiment.

If Earth had a natural moon just outside the atmosphere, it would have
to orbit at this speed; and since at 18,000 mph it takes one and a half
hours to circumnavigate the globe, this would be the duration of the 1.
month."

A month that was shorter than the day sounds an odd phenomenon; but
stranger things happen on other planets.

At greater distances from the Earth, less speed is necessary to counter
the weakening gravitational pull, so the period of revolution steadily
increases; 1,075 miles up, it is exactly two hours, or one-twelfth of a
day.  For many purposes, such as regular tracking from ground stations,
it is convenient to have satellites "geared" to exact ratios of the
Earth's rotation; the twelve-hour orbit is particularly useful.  But
the most valuable of all is the twenty-four hour or synchronous, orbit,
which permits a satellite to hover apparently motionless over one spot
on the globe.  The idea of a body hanging fixed in the sky seems more
than a little uncanny, but of course such a "geostationary" satellite
is not really motionless.  It is merely turning through space at the
same rate as the Earth; and in order to do that at a distance of 26,000
miles from the center of rotation, it has to move along its orbit at
almost 7,000 mph-very far from standing still.  Figure 12, which is
drawn to scale, shows the altitudes at which these various phenomena
occur.

Although it is simplest to talk about circular orbits, all real ones
are elliptical, as explained in Chapter 6. In some cases, the
ellipticity-or eccentricity, to use the correct term-can be very high,
a satellite coming to within a few hundred miles of the Earth and then
rising tens of thousands of miles out into space at its far point.
Oddly enough, the eccentricity does not affect the period of a
satellite; that is determined only by the length of its longest axis.
Elliptical orbits are sometimes referred to as 11 egg-shaped," but this
is incorrect, since eggs are-usually more pointed at one end than the
other.  An ellipse is perfectly symmetrical about both axes.

The dimensions of an orbit and its eccentricity are its two most
important characteristics; but they do not define it completely, for it
can be tilted at any angle to the Earth's axis.  From the practical
point of view, it is easiest to launch a satellite in the equatorial
plane, because when it takes off it can get the maximum boost from the
1,000 mph of spin available there.  Unfortunately, equatorial sites
tend to be politically unstable, though in 1967 the Italians neatly
avoided this in their San Marco project by launching from an
oil-drilling rig in the Indian Ocean.  (For very large spacecraft,
ocean launches may one day be mandatory.)

At the other extreme from the equatorial orbit is the polar one, which
is slightly more difficult to achieve, since it cannot take advantage
of the

Earth's spin.  This handicap is more than offset by the fact that a
polar satellite, in

Moonrise In The Weste97

2-hour orbit

4our orbit

'on

Earth's rotation in one hour 1,0758,000

12,000 6,000 20,000Fig.  12.  Angular speeds ol satellites.

the course of a few revolutions, can observe the entire surface of the
globe, whereas an equatorial one is limited to low latitudes.

It is also perfectly possible to launch a satellite against the
direction of the Earth's spin, so that it has what is -known as a
retrograde orbit.

If it were exactly retrograde moving from east to west, as the natural
celestial bodies appear to do-it would require an extra 2,000 miles an
hour of launching speed to overcome the effects of the Earth's
rotation, and there would be little point in such a fuel-wasting
procedure.  But satellites that are very slightly retrograde-a few
degrees "backward" from the orbit over the poles-do have some valuable
properties (see pp.  100-101).

The ground track of a satellite-the path it traces over the surface of
the

Earth-may be almost as important as its orbit.  It determines the
regions from which the satellite can be observed by ground stations,
either electronically or optically.  It also determines the areas of
Earth which the satellite itself can observe and the frequency with
which it can view them, obviously a deciding factor for meteorological
or reconnaissance satellites.

The very simplest case is that of the equatorial satellite; it remains
always above the equator and retraces the same path forever.  It will
go over the same spot once in every orbit, at regular intervals
determined by its period of rotation.  The only exception is the
stationary satellite, which always stays over one spot and may thus be
regarded as having an infinite period.

A satellite in a polar-90-degree-orbit, on the other hand, will weave a
pattern embracing the entire Earth as it shuttles from north to south,
and the planet turns beneath it.  A similar kind of basketwork pattern,
but spanning a narrower band of latitude, is traced out by satellites
launched in inclined orbits.  The typical Cape Kennedy ground track,
made familiar to millions by the Mercury and Gemini flights, is that
shown in Figure 13.

Satellites with unusual periods and angles of inclination can produce
the most extraordinary ground tracks, forming loops, apparently going
backward, and so on.  All these cases can be worked out with the aid of
a globe, as long as one remembers that the plane of the orbit stays
fixed in space, while the Earth revolves at a uniform speed inside it.
Highly instructive models can be purchased from educational stores to
illustrate all these cases, so no attempt will be made to describe them
here.

The stability of an orbit is obviously a matter of the greatest
practical importance, especially for expensive satellites, which must
operate for many years to pay for themselves-either scientifically or
commercially.

However, there are two kinds of stability to be considered.  The first
involves a satellite's lifetime-how long it will remain aloft before it
re-enters the atmosphere and is burned up (or recovered).  The second
and more subtle point is: how long will the satellite remain in its
original orbit?

As far as lifetime is concerned, the simple answer is that a satellite
will stay up forever, as long as no part of its orbit ever enters the
atmosphere.  But if the lowest point of the orbit (the perigee) is
close enough to Earth for there to be any appreciable air resistance,
the satellite is bound to come down sooner or later.  Every time it
slices into the

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atmosphere, it loses a little of its energy, so it does not rise quite
so far out into space the next time around.  The far point (apogee)
therefore steadily descends, coming closer and closer with each
revolution-thougb perigee remains almost unaffected.  To put it
expressively though not quite accurately, the satellite spirals in
toward Earth.

At last, the orbit becomes perfectly circular; apogee and perigee are
identical.  The orbit is now wholly inside the atmosphere; resistance
is acting over the entire path, and the satellite has only a few hours
of life remaining to it.  Unless it is a heavily protected re-entry
vehicle, designed to survive the thousands of degrees of beat produced
by boring through 5 miles of gas in every second, it will burn up in a
spectacular display of artificial meteors.

The period of a satellite in the closest possible orbit, just before
the final catastrophe, is almost precisely 90 minutes (the very last
orbit is completed in about 84 minutes).  This means that, by pure
coincidence, during the last few days of its life every satellite makes
exactly 18 revolutions in every 24 hours, and so retraces the same path
over the surface of the turning Earth, day after day.

So, in the spring of 1958, millions of people throughout Europe were
able to watch, at almost the same time every night, and moving along
the same track through the constellations, the brilliant star of
Sputnik 2 carrying the corpse of the dog Laika.  This nightly
death-watch for a dying satellite may well be repeated, with far deeper
emotions, in the years ahead, as some future space mission terminates
in a celestial funeral pyre.

This fate can never befall a satellite whose perigee is more than 1,000
miles from Earth-still very close indeed, as cosmic distances go.  But
though an orbit may be stable, it is not necessarily permanent; there
are forces at work which may slowly change it.

Among these are the gravitational attractions of the Sun, Moon, and
planets, engaged in an endless tug-of war  Their influence, however, is
very small, at least for satellites close to the Earth.  But one
"perturbation" which is not small is that due to the Earth itself.

If our planet were a perfect sphere, with a uniform distribution of
matter inside it, a satellite would always repeat the same orbit.  But
in the real case, the Earth has a pronounced equatorial bulge, as well
as other less conspicuous dents and bumps.  The polar flattening
produces a most important effect known as precession, which is well
demonstrated in the case of a spinning top.

When a top loses its speed and begins to fall over, the downward pull
of gravity has a paradoxical effect on its behavior.  The axis of the
top, which until now has been fixed vertically in space, starts to
trace out a conical path.  Anyone who has ever played with a toy
gyroscope and has noticed how it appears to move at right angles to the
Airection in which a force is applied has observed the phenomenon of
precession in its clearest form.

A satellite whirling around the Earth is in effect an enormous
gyroscope, several thousand miles in radius, and the plane of its orbit
tends to remain fixed in space.  This indeed happens, when the orbit is
directly over the equator, and its axis coincides with the Earth's. But
when the orbital plane is tilted, the attraction of the Earth's
equatorial bulge can then come into play, and the orbital plane begins
to twist, so that after a few thousand, or a few million, revolutions
it may have precessed around a complete circle.

By selecting the right inclination, one can choose any rate of
precession desired.  This has been used to advantage, in the case of
some meteorological and reconnaissance satellites, to produce an orbit
whose plane makes one

Radio relay

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&,.

Ra 10 5.0m iolar met, Refueling zone _!"ati-n orbi(I 1/~1-3 hour
orbits)

Ice

Met and as tro station (12-24-hour orbits)

Radio relay

Fig.  14.  Applications satellites.

revolution every year.  Such an orbit is called "sun synchronous"; it
exactly cancels out the Earth's annual rotation around the Sun, and a
satellite moving in it passes over the same spot on the Earth at the
same time every day.  The United States Air Force's Samos
reconnaissance satellites have this useful characteristic, so that they
can re-photograph the same areas under identical illumination.  To do
this, they have to be launched into a slightly retrograde orbit, tilted
about six degrees backward from the axis of the

Earth.  Who would have thought, even a decade ago, that the intricacies
of celestial mechanics would one day be of military importance?

Magnetic and electrical effects in space can also produce minor effects
upon satellite orbits; more surprisingly, so can the pressure of
sunlight, as discussed in Chapter 24.  Feeble though it is, as it acts-
continuously it can produce large effects on satellites of low density,
like the Echo balloons.  These huge but flimsy structures have been
"blown" hundreds of miles out of their original orbits by the pressure
of solar radiation.

To sum up, then, it is possible to establish satellites in orbit around
the

Earth at almost any distance, eccentricity, and angle in inclination.

Figure 14 shows just a few of these, with their scientific and
technical applications.

This illustration was prepared in 1950 for the first edition of The
Exploration of Space, and I see no purpose in altering it; the next two
chapters will describe how all these concepts, and more, have now been
realized.  "However, two comments may be in order.  The first is that
even now we do not have direct links between relay satellites, and
there ate some slight advantages in this.  The second is that the "Met
and Astro Stations" are shown at an altitude which no one could have
then guessed was occupied by the intense radiation of the Van Allen
belt, not discovered until eight years later.

This does not invalidate the diagram.  If we find these orbits useful
for manned stations, that will be just too bad for the Van Allen belt.
We will simply sweep it up.

OPENING SKIES

It is rather amusing, in the second decade of the Space Age, to look
back on the hopes and predictions of those who first proposed the
launching of artificial satellites-and to see how modest they were in
the light of later achievement.  In 1954, for example, the Space Flight
Committee of the

American Rocket Society prepared a report for the National Science

Foundation on "The Utility of an Artificial Unmanned Earth Satellite."
Some of the points it father diffidently made were:

ASTRONOMY AND ASTROPHYSICS.  A satellite could overcome some of the
limitations on observations made through the atmosphere.  GEODESY
(INCLUDING NAVIGATION AND MAPPING).  The size and shape of the earth,
the intensity of its gravitational field, and other geodetic constants
might be determined more accurately.  Practical benefits to navigation
at sea and mapping over large distances would ensue.

GEOPHYSICS (INCLUDING METEOROLOGY).  The study of incoming radiation
and its effects upon the earth's atmosphere might lead eventually to
better methods of long-range weather prediction.

Within five years of the committee's report, all these forecasts had
been amply demonstrated; within ten, the sciences mentioned were
undergoing something like a revolution.  And this was entirely due to
the fact that, for the first time, it had been possible to establish
observing stations above the atmosphere.

In the first few years of the Space Age scores of "scientific"
satellites were launched, carrying instruments for hundreds of ex
eriments.  Some were extremely simple; .P others, like the Soviet
Union's giant "Proton" satellites, nothing less than orbiting physics
labs.  Even to list them would take pages, and to describe the results
they have obtained has already required many volumes.  At the

Goddard Space Flight Center, Maryland, where the instrument readings
are stored for later analysis after they have been relayed to earth,
hundreds of thousands of reels of magnetic tape are stacked in endless
rows while the scientists try to cope with the flood of new knowledge
pouring down from the stars.

Only a few typical or unusually interesting satellites will be
described here, together with a sampling of the results they have
obtained.  But which of those results are the most important we may not
know for generations.

Only time will tell what secrets are now bidden away in the vaults at

Goddard, waiting to demolish long-held theories or to establish new
ones.

For simplicity, it would be hard to beat the "balloon" satellites, of
which

Echo I was the first and most famous.  On June 24, 1966, NASA launched
a singularly perfect specimen, the 100-foot-diameter Pageos, which
looks exactly like a giant, highly polished ball bearing.  Made of
mylar film 0.0005 inch thick, Pageos weighed only 120 pounds and when
inflated in orbit was half a million times larger than the canister
into which it had been skillfully packed.  Moving in a polar orbit at
an altitude of 2,600 miles (period 181 minutes), it is easily visible
to the naked eye (Plate 8).

Its purpose is geodesy-the mapping of the Earth to a degree of
precision never before possible.  Surveyors thousands of miles apart
can observe it simultaneously and photograph it as it moves across the
stars; when analyzed, these photographs will allow points on the Earth
to be fixed to within about ten yards.  Similar results have also been
obtained by using satellites carrying flashing strobe lights (Anna I-B,
1962) or mirrors reflecting back laser beams (Geos 1, 1965), but Pageos
requires the minimum of ground equipment.

High-precision studies of orbits made possible by satellites of this'
type have already revised our knowledge of the Earth's shape.  It is
nota simple flattened sphere (ovoid); there are bumps and bulges which
will tell us much about its evolution and the distribution of matter
in

Plate 8. The Pageos satellite.

NASA

its interior.  Of course, these deviations from the ideal shape are
very small-utterly invisible to the eye of the astronaut looking back
at his borne from a few thousand miles away.  But they are of great
importance scientifically, and it is a curious thought that knowledge
of the Earth's interior can best be obtained by going far out into
space.

However, most of the instrumentation aboard satellites has been
designed to study the environment through which they pass, and
undoubtedly the greatest discovery yet made is that due to the very
first United States satellite,

Explorer 1 (1958).  This revealed, as someone put it expressively, that
"space is radioactive," and for a while there was considerable alarm
about the effects of this discovery upon orbiting astronauts.

We now know, thanks to Explorer 1 and its much more elaborate
successors, that our planet is surrounded by a huge radiation belt,
roughly doughnut-shaped, with the Earth in the hole.  The inner part of
the belt-named after its discoverer, Dr.  James Van Allen-consists
mostly of positively charged protons (hydrogen nuclei) and reaches its
maximum intensity at a height of about 500 miles.  In the outer zone,
negatively charged electrons predominate, with their maximum intensity
at 10,000 miles.  At one time it was believed that there were two
separate belts, but it is now known that they merge into each other,
though they are separated by a region (about 8,000 miles high) where
the intensity of radiation is a minimum.  There is also very little
radiation over the poles; it all lies above the equatorial and
temperate zones.

The great radiation belt is produced by streams of electrons and
protons from the Sun, which have become trapped in the Earth's magnetic
field.  As a result there is an extremely complicated interrelation
between solar and terrestrial magnetic-activity, both of which vary
with time.  For tens of thousands of miles around the Earth there is an
invisible cloud of electronic and pro tonic "weather," with its storms
and winds and calms, never suspected until our generation.

The great radiation belt is not symmetrical; the gale of charged
particles "blowing" from the Sun compresses it on the daylight side of
Earth and makes it trail out on the night side.  The doughnut is
therefore badly distorted three or four times thicker on one side than
on the other.  At its outer fringes it merges imperceptibly into the
(very weak) general background of radiation between the planets.

Almost every scientific satellite launched from the Earth -as well as
many space probes on greater journeys-has carried instruments to
measure the ever-changing phenomena in the great radiation belt.  A
good example is the

Orbiting Geophysical Laboratory (OGO), of which the third, and first
fully successful one, was launched on June 6, 1966.

OGO 3 has an orbit specifically designed to sample an enormous volume
of the near-Earth environment.  Its perigee is only 170 miles up, but
its apogee is 75,800 miles from Earth, or one-third of the way to the
Moon.

Completing this very elongated path once every two days, it reports -on
the energy and concentration of the protons and electrons in the
radiation belt, fluctuations in the Earth's magnetic field, radio
propagation characteristics, cosmic rays, interplanetary dust, radio
noise-to mention only some of the twenty-one separate experiments it
conducts.

One of the most important-and most uncertaincharacteristics of the
space environment before artificial satellites became available was the
frequency of meteoroids; some pessimists believed that any spacecraft
would be riddled by cosmic mac bine-gun fire as soon as it left the
protective blanket of the atmosphere.  In fact, meteoroids have turned
out to be so rare that it is quite difficult to accumulate reliable
statistics about them, and rather heroic efforts were needed to do so.
Perhaps the most impressive of these, were the launchings of the three
huge Pegasus satellites (February 16, May 27, July 30, 1965) by the
last three of the

Saturn 1 rockets.  In orbit, the Pegasus satellites extended vast
"wings," almost a hundred feet across, which consisted of thin aluminum
panels, varying in thickness between 1.5 and 16 thousandths of an inch.
These panels were connected to electrical circuits which reported any
meteoroid penetrations, and signaled them back to Earth.  After many
months of successful operation, the three Pegasus satellites showed
conclusively that, at least for flights of short duration, meteoroids
were nota serious danger

The ionosphere-that electrified layer in the upper atmospl;ere which
reflects radio signals back to Earth, and so makes long-distance
communication possible around the curve of the globe-is one piece of
near-space that has been of tremendous scientific, commercial, and
military interest for half a century.  It is not surprising, therefore,
that dozens of satellites have been launched to investigate it.  One of
the first and most successful was the Canadian Alouette (lark), sent
into a 600-mile-high polar orbit on September 29, 1962.  It carried a
radio transmitter which swept continuously across the VHF
(very-high-frequency) band; after the signals from this "topside
sounder" had passed through the ionosphere, they were picked up by
ground stations and their intensity gave a measure of the electron
density in this region.  Ionospheric probing was also the main purpose
of the first United Kingdom satellite, Ariel I (April 26, 1962).

Its instruments measured

0 Note on terminology: a meteoroid (usually micro meteoroid is a small
solid object moving through space; a meteor is the streak of light it
produces when it enters the atmosphere; a meteorite is what remains in
the rare cases when it reaches the ground.  The words are often used
interchangeably.

and sampled the charged particles between 242 and 754 miles above the
Earth.

From the scientific point of view, perhaps the most exciting satellites
are those which, although they may be within a few hundred miles of the
Earth, are looking outward to deep space.  For by lifting our
instruments through a distance which is quite trivial, even by
terrestrial standards, we have been able to obtain a completely new
view of the universe.

Until our age, astronomers had to make all their observations from the
bottom of the atmosphere.  As a result, they were rather like
color-blind men straining their eyes through a fog-or, to use a
well-known and not inaccurate analogy, like fish peering upward from
the bottom of a muddy pool.

On a clear, moonless night, when we look up at the stars, it seems that
there is nothing to obscure our view.  But this is an illusion-the
result of evolutionary necessity.  Our eyes have, naturally enough,
adapted themselves to use the light which passes through the
atmosphere, and that is only a small fraction of the radiations that
fall upon the Earth from space.  Most of them, luckily for us, are
completely blocked by the 100-mile-thick gaseous shield above our
heads.

The complete range of the electromagnetic spectrum that is, all
possible types of wave that can pass through space-is shown in Figure
15, which also shows the regions in which the Earth's atmosphere is
normally transparent.

It will be seen that there are a number of 11 windows" through which
radiation can penetrate; the most ipportant is that centered around
visible light, but a second one-the radio window-has been opened in our
lifetimes and has given rise to the vast new science of radio
astronomy.

Between and beyond these windows there is partial or complete opacity.
Even a few feet of atmosphere acts like a brick wall to the very short
waves of the spectrum, such as the X rays and the far ultraviolet.
Ground-based astronomers had no way of telling if such waves existed in
space, but they could be certain that, if they did, they would carry
priceless information about the Sun and stars.

-a a > -c -5 Radio wavescc

~-3 11~2 to'-, 1 10 102 10, 10-2 10-1 1 10 to, to,

Microns Motors (millionths of a motor)

Fig.  15.  The transparency a/ the atmosphere at varying wave
lengths.

The Orbiting Solar Observatory (OSO) and Orbiting Astronomical
Observatory (OAO) were very complex satellites designed to explore this
hitherto unseen universe.  OSO-A was launched on March 7, 1962, and
observed the Sun for 2,000 hours during its operational lifetime.  OSO
2 (February 3, 196$.) was also successful, but the third, OSO-C (August
2~, 1965), failed to orbit.

The satellites were of unusual design, consisting of a spinning wheel
on the axis of which was mounted a semicircular "sail" carrying
instruments pointing with great precision at the Sun.  These
instruments measured and analyzed the solar radiation in the X-ray and
the far-ultraviolet region.

There are at least two reasons why this particular radiation is of
major importance.  Unlike visible sunlight, it shows great fluctuations
in intensity, as a result of gigantic eruptions, or "flares," on the
surface of the Sun.  Sometimes these outbursts cause such violent
changes in the ionosphere that they completely disrupt long-distance
radio communications.

It is also possible that they may have some effect upon the weather.

Even more serious, as we move into the Space Age, they may herald the
advent of ionized gas clouds leaping from Sun to Earth, and so could
give warning to astronauts of "solar storms."  As manned space flight
becomes more common and more widespread, it will be essential to keep a
regular patrol of Sun-watching satellites.

The first Orbiting Astronomical Observatory was launched on April 8,
1966.

It contained a battery of telescopes (the largest having an aperture of
16 inches), and with its 440,000 separate parts and 30 miles of wiring
was, at that time, one of the most complex satellites ever developed.
It was injected into a perfect orbit, but within a few hours something
went wrong with its power supply and its signals slowly faded out.  In
its first attempt to see the unknown universe of ultraviolet stars and
nebulae, the United

States had gambled enough to build half a dozen Mount Palomar
telescopes-and had lost.

At the other end of the spectrum, there is also unknown territory
represented by the very long radio waves which are reflected back into
space by the upper surface of the ionosphere and so do not normally
reach ground level.  The waves concerned are those longer than 30
meters (100 feet), and to study them properly it will be necessary to
use very large antenna systems.  The Canadian Alouette pioneered in
this field by carrying antennas rolled up like steel rules, and these
have been developed now to such a degree that a small drum can extrude
an antenna several hundred feet long.  The really advanced radio
astronomy satellites, however, will probably be in the form of spinning
webs; design studies show that centrifugal force would permit the
automatic deployment of antenna systems which may be tens of miles in
diameter, yet may weigh only a few hundred pounds.

The heartbreaking demise of the first multimillion-dollar Orbiting

Astronomical Observatory-which might have been saved had there been a
man on the spot with a screwdriver-strongly suggests that the very
large and complex scientific satellites of the future will be designed
for easy servicing, even if they are not permanently manned.  As a step
in this direction, a large number of experiments were carried out by
the Mercury and Gemini astronauts.  Plans for the next stage-the
orbital laboratory-will be discussed in Chapter 12.

Meanwhile, the robot probes which have been leaving the atmosphere in
such numbers have already started a revolution, comparable to that
which began three and a half centuries ago when Galileo pointed his
first crude 11 optic tube" at the heavens.  Every breakthrough in
instruments produces a corresponding breakthrough in knowledge; the
satellites have given us new eyes and ears, and for a long time to come
we will be dazzled and deafened by the information they bring us.  But,
later, we will begin to understand.

Plate 9. Unmanned orbital telescope.

American Institute of Aeronautics and Astronautics, Inc.

FIRST HARVEST

In the last chapter we glanced briefly at the new knowledge now being
obtained by artificial satellites; in this one we shall look at their
practical uses.  It is essential to realize, however, that this is a
very arbitrary distinction, and the dividing line is constantly on the
move.  All really great advances in technology, as opposed to mere
gadgetry, arise from scientific discoveries which at the time seem to
be of no relevance to everyday life.  Electric power and light were
made possible because men like

Faraday played with magnets and coils of wire, trying to understand the
workings of nature and sometimes even taking a perverse pride in the
invariably mistaken belief that their discoveries.  would never be of
use to anybody.  Yet always, a generation or two later (a decade or two
later, nowadays), the Edisons come along and turn their "pure" science
into bi

Ilion -dollar industries.

As yet, the magnetic fields in space, the great radiation belt, the
harmonies of the Earth's gravitational field, the solar wind, and
similar exotic phenomena have little value in the marketplace.  But
their time will come.

Meanwhile, there are types of satellite which have obvious and
immediate practical uses, which everyone can appreciate and many
millions can indeed share.  These are the so-called applications
satellites, which do not gather scientific facts, but work for a
living.  (Many do both, for applications satellites usually carry
instrumentation of various kinds.) As already mentioned in Chapter 1,
the first fictional 112

project for an artificial satellite-Hale's "Brick Moon"-was an aid to
navigation.  Indeed, it is hard to see what other use could have been
imagined in 1869, since no practical way then existed of collecting
information automatically and sending it over great distances.

Probably no one would have been more surprised than Hale to know that
his inspired fantasy came true in less than 90 years, though it did so
with the aid of techniques of which He could scarcely have dreamed. His
brick MOOD was to be observed visually, like any other of the celestial
bodies, which meant, of course, that it would be useless in daylight
and in cloudy weather.  The navigational satellites of today make their
presence known by radio and so can be tracked under any conditions.

The first to be launched, Transit 1 B (April 13, 1960), carried two
radio beacons and utilized the Doppler effect the change of pitch of a
signal with varying speed.  The operation of the system can best be
imagined by this analogy: Suppose you are standing at some distance
from a railroad track and that a train passes with its whistle blowing.
While the train is approaching, the whistle will seem to have a higher
frequency than normal; while it is receding, the frequency will be
lower than normal.  Only at the moment of closest approach will you
hear the whistle's note as it really is; if you possessed what
musicians call perfect pitch, you could pinpoint this moment and would
know, even without being able to see it, when the train was nearest to
you.

The Transit satellite is the train, and because its orbit is known with
great precision, it runs to a more accurate timetable than any
railroad.

The radio beacon provides the whistle; by analyzing its rate of change
of pitch, ship or air-borne electronics sys terns can obtain a "fix"
with an accuracy of one-tenth of a mile.

A series of Transit satellites was launched between 1960 and 1964; they
included the first satellites ever to be powered by nuclear energy, and
the system became operational in July, 1964.  Although at first its
main customers were the Polaris submarines, it is Dow available for use
by all ships which fit the fairly simple receivers and computers
required; oceanographic survey vessels have particularly benefited by
it.

More advanced systems are now being developed which will involve
satellites fixed in the 24-hour stationary orbit

I "' - " "I

Plate 10.  Three hurricanes visible on a map-photo compiled Irom
pictures taken by the ESSA #5 weather satellite in September, 1967, and
transmitted via ATS 1. NASA

above the equator; this arrangement will be much simpler and will
permit a far wider range of users.  The time will come, in the
not-too-distant future, when a wristwatch sized computer turned to the
Navsat network will tell a man exactly where be is anywhere on the
surface of the globe, and no one need ever again be lost, even in the
remotest corner of the world.

Now that millions of TV viewers are accustomed to seeing, in their
regular weather forecasts, photographs of cloud cover over whole
continents, it may seem surprising that anyone ever doubted the utility
of meteorological satellites.  Yet their value was no tat first obvious
even to the experts, as I can testify from personal knowledge.

When the American Museum of Natural History's Hayden Planetarium asked
me to arrange its 1954 symposium 9n space flight, I wrote to Dr.  Harry
Wexler, chief of research of the U.S. Weather Bureau, suggesting that
be should present a paper on the meteorological uses of satellites.  I
was somewhat taken aback when be replied that they would be of very
little value.  After brooding aw bile I wrote again, challenging him to
demonstrate this-if only to stop us space cadets from wasting the
valuable time of the meteorological authorities.  To his credit, Dr.
Wexler accepted the challenge; by the time he had written his paper, he
had converted himself completely.  Afterward he became the United
States' chief protagonist for this new research instrument and played a
major role in the development of meteorological satellites until his
death in 1962.  Perhaps I should add that Dr.  Wexler's attitude was
precisely correct and demonstrates all the stages (skepticism, inquiry,
enthusiasm) a scientist should pass through when confronted with some
novel and (in this case literally) far-out idea.

The first meteorological satellite, Tiros (Television and Infrared

Observation Satellite) was launched on April 1, 1960, into an almost
circular orbit a little more than 400 miles above the Earth.  Because
its orbit was inclined to the equator at an angle of 48 degrees, during
the course of every few revolutions it ranged over half the surface of
the globe.  As the first of its 22,500 photographs was received by the
ground stations, the meteorologists realized that they had, as one of
them put it, "gone from rags to riches overnight."

Seven further satellites were launched in the Tiros series between
April, 1960, and December, 1963, all into similar orbits with periods
of 100 minutes.  Most of them equaled or exceeded their designed life,
and between them they sent back to earth several hundred thousand
photographs.  In addition, they carried instruments that could measure
the flow of heat from our planet back into space information vital to
the meteorologist but previously unobtainable.

The last of the Tiros series-9 and 10-were even more successful; they
were launched into bigb-inclination (81-82-degree) orbits so that they
passed almost over the poles and gave virtually global coverage.
Similar orbits were used by the still more advanced Nimbus and ESSA
(Environmental Science

Services Administration) satellites, which have continued and extended
the work begun by Tiros, establishing the world's first operational
weather satellite system.  Today any electronic enthusiast with a few
hundred dollars and a certain amount of ingenuity can build a simple
ground station that can interrogate the ESSA satellites as they pass
overhead, and can read off, on a cathode-ray tube or commercial
facsimile receiver, the weather picture for a thousand miles around
him.  This Automatic Picture

Transmission (APT) system was introduced with Tiros 8 in December,
1963, and has made the i nultimill ion -dollar satellites freely
available to any country or any individual who cares to use them.

The first high-definition photos of an entire hemisphere, made by a
satellite sufficiently far from Earth to show it as a planet, were
obtained in December, 1966, from the first of the Applications
Technology

Satellites.  Stationed over mid-Pacific, ATS 1's special electronic
camera produced superb studies of changing cloud patterns over almost
half the

Earth (Plate 13); these were later combined to give speeded-up movies
so that meteorologists could watch the circulation of the atmosphere
with their own eyes, thus learning in a few minutes facts which might
never have been revealed in years of ground-based observations.

It is probable that the various met sats have already paid for
themselves many times over.  They have detected hurricanes far out at
sea, hours before their existence could have been discovered in any
other way.  They have improved the quality of weather forecasting, with
all that this implies to human wealth, productivity, safety, and

Plate 11.  A Hughes Aircrall Company engineer encircled by the antennae
of the 790-pound ATS 1 communications satellite.  Hugbes Aircraft
Company

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Plate 12.  The ATS communications satellite: sectional view.

Hughes Aircraft Company happiness.  It has been claimed that really
accurate prediction of rain, snow, monsoons, and other meteorological
phenomena will eventually be possible, thanks to the new knowledge from
this source-with savings that have been estimated at tens of billions
of dollars a year.  Looking even further ahead, if weather control or
modification ever becomes possible (or desirable, which is no tat all
the same thing), it can hardly be attempted without the complete
understanding of atmospheric processes that only satellites can
provide.

The ATS satellites, built by the Hughes Aircraft Company and exploiting
the technology its engineers developed for Syncom and Early Bird (see
pp.  125-129), may be regarded as a series of space buses for testing
various practical applications of satellites.  In addition to obtaining
meteorological information by their own onboard cameras, they can serve
as communications links in an elaborate data-collecting system,
relaying information from dozens of ground stations.  This information
includes readings from rainfall gauges, oceanographic buoys, met
balloons-and possibly beacons attached to large land and marine animals
for zoological research.

Probably the most interesting, and doubtless the most advanced, of the
applications satellites are those about which nothing has been
published; in some cases, even their names are classified.  I refer, of
course, to the military reconnaissance satellites.

In his 1929 book Hermann Obertb had already pointed out that a manned
space station could be used to watch the movements of warships.  With
the development of TV techniques and camera-carrying capsules that
could be recovered from orbit, satellites became of intense interest to
the military, particularly after the 1960 U-2 debacle had proved the
vulnerability of reconnaissance aircraft in the missile age.  It is
true that a satellite can also be destroyed, perhaps more easily than
it can be launched.  But there is a very important distinction; even
the people who use reconnaissance aircraft admit that they are illegal
and apologize when they are caught, for they are operating in another
country's airspace.

Satellites, however, fly only in the no-man's-territory beyond the
atmosphere and are at liberty to take as many pictures as they please.
It is true that for a while the Soviet Union considered that they were
provocative and Unfriendly, but since it too started using them in
large numbers, very little has been heard of this objection.

The United States Air Force has, naturally, been most active in this
field; it orbited its first Samos reconnaissance satellite on January
31, 1961, and since then has launched dozens of anonymous payloads,
mostly into polar orbits at fairly low altitudes, so that they can
thoroughly scrutinize the whole Earth.  The quality of the resulting
photographs may perhaps be judged by some of those sent back from the
Moon by the Orbiter vehicles (Plate 14).  Where there is physical
recovery of the capsules (as happens with the

Discoverer satellites), the definition may well be much higher.
Although haze and cloudiness set operational limits to the system, the
photographs brought back by the Gemini astronauts show the astonishing
amount of detail that can be observed from space when the atmosphere is
clear (Plate 15).

There are some military satellites which do not depend on light waves
and so are less affected by weather conditions.  The Midas satellites
were designed to spot ICBM launchings by detecting the immense amounts
of infrared radiation produced by rocket exhausts.

Other space vehicles listen in to radar and communications networks;
yet others are involved in precision mapping and navigation.  (The
Transit program, mentioned previously, was classified for some years
because of its military applications.) And particular mention should be
made of the VELA, or Sentry, satellites, which swing slowly along
almost circular orbits 70,000 miles above the Earth, waiting to detect
clandestine nuclear explosions.

The Soviet Union has its counterpart to this program, though it talks
about it even less than does the United States.  As long ago as
December, 1965, it reached number one hundred in its rather mysterious
Cosmos series, most of which return to Earth after a few days'
traveling along close, high-inclination orbits.  It may be doubted if
their purpose is always entirely sicentific.*

On balance, these satellites have probably had a stabilizing effect
upon international affairs; they have made a reality of President
Eisenhower's imaginative "Open Skies" proposal.  The advance
announcement of Chinese nuclear tests by the United States proves that
it is now impossible for one country to conduct military preparations
without the knowledge of the two super powers; nor can these hide
anything from each other.  It has been stated that the United States
reconnaissance satellites have already paid for the entire space
program-for by revealing that the Soviet Union's missile deployment was
not as fast as had been feared, they allowed the

Department of Defense to establish more modest goals for its own ICBM
program.  The Samos satellites have been worth many times their weight
in gold to the United States taxpayer.

A few months before Sputnik 1 opened the Space Age, the following
wild-eyed prophecy appeared in print: "It may seem premature, if not
ludicrous, to talk about the commercial possibilities of satellites.
Yet the airplane be

* Some of these-e.g."  Cosmos 57 (February, 1965)-have exploded into
hundreds of fragments, to the great annoyance of the satellite tracking
networks.  It has been suggested that this was to prevent them from
descending on United States territory.

The Boeing Company came of commercial importance within thirty years of
its birth, and there are good reasons for thinking that this time scale
may be shortened in the case of the satellite, because of its immense
value in the field of communications" (The Making of a Moon, Clarke,
1957).  The first $100 million of Comsat stock went on the market seven
years later (June 2, 1964) and promptly disappeared into myriad safety
deposit boxes.

The idea of employing satellites as radio relays, so that all possible
wavelengths-including light, if desired-could be used for
communications purposes, now seems a rather obvious one, and it is
somewhat surprising that it did not appear until 1945.  It is true that
Obertb, in his 1929 classic, The Road to Space Travel, mentioned that
manned space stations could signal to remote parts of the Earth by
flashing heliograph mirrors, which today seems a very primitive idea.
We tend to forget that the astonishing developments in electronics,
miniaturization, and communications techniques which now permit us to
control room

Plate 13.  Cloud patterns over Earth, photographed by ATS 1.

P-h- Aircraft Company bots on the surface of the Moon, or in orbit
around Mars, have become possible only since World War II.  Willy Ley
once pointed out that when

Oberth wrote his book, the only long-range radio stations in existence
used antenna systems acres in extent, supported by towers hundreds of
feet high.  The idea that this sort of equipment might one day be
squeezed into a bat box would then have seemed slightly more fantastic
than space travel itself.  Even as late as 1945 I still assumed that
communications satellites would be large, manned structures.  Several
years of battling with balky electronics had convinced me that it was
essential to have a servicing engineer on the spot; I have modified
this position only slightly.

The simplest type of communications satellite is passive, an orbiting
radio mirror which reflects signals back to Earth without itself
modifying them in any way.  Such was the giant Echo balloon, launched
on

August 12, 1960, into a 1,000-mile-bigb orbit, and for a long time one
of the most conspicuous objects in the night sky.  Echo I (and its
slightly larger successor Echo 2, launched into a near polar orbit on

January 25, 1964) was used for many test transmissions of speech,
teletype, and facsimile and clearly demonstrated the potential value of
satellites for communications.  However, passive systems (though they
are simple, have nothing to go wrong, and can provide an unlimited
number of circuits) are extremely inefficient; only a tiny fraction of
the power beamed at the Echo balloon actually fell upon it, and an even
smaller fraction of that power was picked up by ground stations.

Although some of these limitations may be overcome (for example, by
replacing the spherical reflector by one so shaped that it sends a much
larger signal back to Earth), passive systems appear to be largely of
historic interest.

Active satellites are true relays, receiving the signal from the ground
station, amplifying it, and rebroadcasting it at greatly increased
power (and at a different frequency to avoid interference).  Such a
system, though complex, is millions of times more efficient than a
passive one; it received its first public demonstration with Telstar 1
(July 10, 1962).  Though the United States Army's earlier

Atlas-Score (December 18, 1958) and Courier (October 4, 1960) had
provided a very limited experimental service with radio signals only,
Telstar heralded the age of inter continental television when it
inaugurated the first live transatlantic program on July 23, 1962.

Telstar was also the first privately owned satellite, and thereby
created another precedent.  It was built by the American Telephone and
Telegraph

Company, which the Bell Laboratories' energetic director of
communications research (and occasional science-fiction author), John
R. Pierce, had dragged singlehanded into the space communications
field. Dr.  Pierce was not only one of the instigators of the Echo
project but was also co-inventor of the special wide-band amplifier-the
traveling wave tube which is the heart of all communications satellites
to date.

Because the rockets then available could not lift large payloads to
very high orbits, Telstar and its Radio Corporation of America
successor, Relay (two of each were ultimately launched), orbited
relatively close to the

Earth; they therefore moved fairly rapidly and remained in view from
any given pair of ground stations for only a few

Plate 14.  Tycho Crater, photographed by Lunar Orbiter 5 Irom, an
altitude ol 135 miles on August 15, 1967.

The Boeing Company

Plate 15.  Photograph of Gemini 7, taken through the hatch window of
Gemini 6 at an altitude of 160 miles during rendezvous maneuvers on
December 15,

1965.  NASA

minutes at a time.  As a result, they could not provide the continuous
type of service essential for commercial operations.

There were two ways of overcoming this difficulty.  One was to use a
whole series of Telstar-type low-altitude satellites, more or less
equally spaced around the world so that there was always at least one
above the horizon at any given point.  The other was to go out to the
synchronous orbit, 22,000 miles above the equator, where a satellite
would appear to stand fixed in the sky, and three could provide a
worldwide service.

The synchronous system was forcefully advocated by Dr.  Harold Rosen of
the

Hughes Aircraft Company, whose Syncom 2 was launched on July 26, 1963.
(Syncom I achieved the correct orbit on February 14, 1962, but because
of an onboard mechanical failure never returned any signals.) This
satellite was stationed over the Atlantic, but because its orbit was
inclined to the equator, it did not remain absolutely fixed over the
same spot.  Instead, it described a small north-south figure eight
every day, but as the ground tracking stations followed its excursions
in latitude, it was available for 24-hour use.

The first satellite that was truly stationary (i.e."  both in a 24-hour
orbit and above the equator) was Syncom 3, launched August 19, 1964,
with the specific intention of covering the Tokyo Olympics, which it
did brilliantly.  After many thousands of hours of operation, the two
Syncoms were handed over to the Department of Defense to provide
reliable transpacific communications; Syncom 2 was "walked" along the
equator by gentle puffs from its control jets, until it had joined its
companion on the other side of the world.

The operational experience provided by the first synchronous satellites
provided the basis for a commercial system and also disposed of a
number of bogeys.  It was obvious from the beginning that a satellite
which appeared to be fixed in the sky would have enormous advantages
over one that must be constantly tracked; perhaps most important, it
would not require movable antenna systems backed up by computers, for
once the ground antennas had been aimed in the right direction, they
could be left pointing that way, and simple television-type arrays
could thus be used.  However, there was a price to be paid for this
simplicity.

In the first place, the synchronous orbit is so far from Earth that
reaching it is quite expensive in terms of rocket fuel.  Surprisingly,
it is harder to put a payload in the 22,000-mile-high orbit than it is
to send it to the Moon.

Moreover, a "stationary" satellite will not stay in one place without
occasional assistance, The perturbations of other heavenly bodies; and
in particular irregularities in the Earth's gravitational held, make it
drift slowly from its initial position, so from time to time it has to
be nudged back on station by corrective thrusts.  Only a very small
amount of fuel is required, even for several years of operation, but
this does add to the complexity of the system.

These problems, and several others of a technical nature, were
triumphantly solved by the Syncom satellites, but there remained a more
fundamentaf one which no engineering advances could remove.  It takes
an appreciable time-about one-fourth of a second-for a radio signal to
climb 22,000 miles and to return to Earth.  If you are talking to
anyone over a synchronous circuit and ask a question, it is a little
more than half a second before you can receive the reply, even if your
listener reacts instant

Plate 16.  Telstar cons inunications satellite.

American Institute of Aeronautics and Astronautics, Inc.

ly.  During that brief but perceptible interval, you may have changed
your mind and started to say something else-so you may be speaking when
the answer comes.  Moreover, unless special precautions are taken, you
may hear the delayed echo of your own voice, and nothing is more
inhibiting to speech than this.

The echo could be dealt "With by suitable circuits; the half-second
delay was a law of nature and had to be lived with.  For a time it was
feared that it might be unacceptable to the public, but in practice it
was found that few people even noticed it, though it may occasionally
cause

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plate 17.  Syncom co-munications satellite: sectional view.

Hughes Aircraft Company trouble to excitable, interruption -prone Celts
and Latins Low-altitude satellites, which would have had shorter time
delays, could therefore be dispensed with, and the much more elegant
synchronous system could be used for telephony.  For radio and
television relaying, of course, there had never been any problem.  No
listener or viewer knows or cares if his program is half a second later
than it might have been, had it come from a nearer transmitter.

The United States moved swiftly to set up an operational
communications-satellite system; the result was the remarkable
semipublic, semiprivate, national-international Communications
Satellite Corporation, established by Act of Congress in 1962. Comsat's
first child, Early Bird, was launched on April 6, 1965* and placed in
service on June 28; it could provide either one TV channel or 240 voice
(telephone) circuits, but not both.  Because of this limitation, the
initial rates were high, and before long Comsat was receiving squawks
of protest from indignant customers.

Exactly the same thing had happened 99 years be * I was present at
Comsat headquarters on that memorable occasion and watched the launch
on closed-circuit TV.  The three-stage thrust augmented

Thor Delta booster was still oil the way up when Vice President
Humphrey started to give us one of his little speeches.  The circuit to
Cape Kennedy was switched off, and it occurred to me that if anything
went wrong now, everyone in the United States would know it except the
staff of Comsat.

They were all listening to the Vice-President.

Plate 18.  The Syncom satellite, without its covering of solar cell
paneling, undergoing tin al checkout.

Hughes Aircraft Company fore, when the first successful Atlantic
telegraph went into operation.  It had taken just under a century to
progress from cable to satellite.

In the spring of 1967 Early Bird was joined by two larger
brothers-Intelsat 2 over the Pacific and Intelsat 3 over the Atlantic.
With these three satellites, all the world's TV networks could be
linked together, and the first global telecast was broadcast on June
27, 1967.

Meanwhile, the Soviet Union had not been idle and had launched Molmya
(lightning) communications satellites of its own, into unusual, highly
elliptical orbits, with a perigee only 300 miles up and an apogee
24,000 miles high.  At first it was thought that Molmya 1 had failed to
go into the synchronous orbit, but it was soon realized that its high
inclination to the equator (65 degrees) and period (almost exactly 12
hours) permitted it to arc slowly high over Russia at the same time
each day.  For a country in northern latitudes, such an orbit has some
advantages over the synchronous, equatorial one.

The first generation Comsats were all low-powered devices, so that
their signals could be picked up only by sensitive receivers coupled to
large antenna systems; the

Plate 19.  Final checkout at the Early Bird Conimunications
satellite.

Hughes Aircraft Company ground stations using them tost $1 million or
more and were linked to the various national television or telephone
networks.  However, many experts believe that the real communications
revolution will start when Comsats are large and powerful enough to
broadcast directly into the home, bypassing the ground stations
completely.  Only in this way will it be possible to open up the
undeveloped countries-Africa, South America, much of Asia-which have
never had, and now may never require, surface communications
networks.

Direct radio (voice) broadcasting from Comsats to simple ground
receivers is already technically possible and could have immense
social, political, and educational consequences.  TN7 broadcasting,
which requires much more power, will take a little longer, but even
here the problems are not so much technical as they are economic and
political-especially the latter, for direct broadcasting obliterates
national and linguistic boundaries and means, among many other things,
the end of censorship.  It is not surprising that some countries are
very worried about it.

Whole volumes and innumerable international conferences have been
devoted to the social impact of space communications Within a lifetime,
they may change our world out of recognition and alter the patterns of
business and society at least as much as the telephone has done.  They
may give us instant "newspapers," with updated hourly editions flashed
on to portable receivers no bigger than this book; they may make all
telephone calls local ones, so that it will be just as quick and cheap
to call a friend at the antipodes as in the next apartment; they may
result in the swift establishment of English (or Russian, or Mandarin
.. . ) as a global language; they may result in the disintegration of
the cities and a great reduction in travel, as telecommunications plus
tele control will allow most men at the executive grade to live
wherever they please.  And there may be even more dramatic changes, for
good or bad, that no one can foresee today-any more than Samuel Morse
or Thomas Edison could have imagined that one day a quarter of the
human race would

* I have combined my essays on the subject in Voices from the Sky,
which also contains a "Short Pre-his tory of Comsats, or: How I Lost a
Billion

Dollars in my Spare Time."  For the propaganda uses of Comsats, see the
short story "I Remember Babylon," in Tales of Ten Work1s.  Though this
is required reading by Comsat staff, I do not wish to raise any false
hopes.

watch the same pictures and hear the same sounds.

Whether we like it or not, the world of the communications satellites
will be one world.  In the long run, the Comsat will be mightier than
the ICBM.

It will put the clock back to the moment before the building of the
Tower of Babel-when, according to Genesis 11: "The Lord said: Behold,
they are one people, and they have all one language, and this is only
the beginning of what they will do; and nothing that they propose to do
will now be impossible for them."

Plate 20.  The Intelsat communications satellite.

Hughes Aircraft Company

JZ

MAN IN ORBIT

The first serious students of astronautics had taken it for granted
that men would be the most important payloads that rockets would carry
into space.

Tsiolkovsky and Oberth had written of little else, and though the
cautious (as well as more practical-minded) Goddard had confined his
few public statements to instrument-carrying vehicles, his private
notebooks leave no doubt as to where his interest lay.  In these, he
went so far as to speculate about refueling bases on the planets-a far
cry indeed from "A Method of

Attaining Extreme Altitudes."

One reason for this attitude was that these pioneers saw, much more
clearly than many who came later, that space travel was the next stage
in man's exploration of his.  environment.  Today's controversies
between the protagonists of manned and unmanned spacecraft would have
seemed to them as pointless as the theological disputes of the Middle
Ages.

The conditions which men would encounter in flight beyond the
atmosphere were well understood long before any rockets had entered
space, and the more conscientious science-fiction writers had quite
accurately described ways of coping with them.  The rise of aviation
medicine from the 1920's onward put these speculations on a more
scientific basis, and when the

Space Age dawned in 1957 there was only one serious unknown.  Every
condition that could be encountered in space was reproducible in the
laboratory, with the single exception of weightlessness.  Rocket
flights with animals (especially dogs and monkeys) in the decade up to
1957 had shown that the apparent absence 133

of weight could be endured for several minutes, so at least there was
no danger, as some had feared, of the heart promptly running amok when
the gravitational load was removed from it.  But the effects of really
prolonged weightlessness were still unknown, and there were plenty of
dire predictions from the pessimists.  I can well recall crossing
swords at an international conference, as late as 1963, with a
distinguished biologist who stated categorically that lack of weight
could not be tolerated for more than a week.

The reason why an astronaut is normally weightless is perhaps more
misunderstood than anything else in the whole business of space travel.
It is nothing to do with being "beyond the pull of Earth's gravity"-not
that such a thing is literally possible in any case.  As we saw in
Chapter 5, most manned orbital flight takes place in regions where
gravity has diminished by only a few per cent from its sea-level value.
Yet, despite this, astronauts weigh exactly nothing once their rockets
have ceased to thrust.

This confusing paradox is largely due to poor semantics.  On Earth we
tend to use the words "weight" and "gravity' interchangeably, because
in almost all terrestrial situations the two phenomena occur together.
But they are really quite separate entities and can exist independently
of each other; in space they normally do so.  On occasion, however,
they can be separated even on Earth, as will now be demonstrated. (This
is another Einsteinian "thought experiment"; carry it out at your own
risk.)

If you place a set of bathroom scales on a trapdoor and stand on the
platform, the pointer will indicate your weight.  But if the trapdoor
is opened, the reading on the scales will drop instantly to zero.
Nothing has happened to the Earth's gravity~ but your weight has
vanished!

For weight is a force, normally produced by gravity, and you cannot
feel a force if it has "nothing to push against," to use a familiar
phrase.  You do not feel any force when you push against a swinging
door; you cannot feel any weight when you have no support and are
falling freely.  And an astronaut, except when he is firing his rockets
or re-entering atmosphere, is always falling freely.  The "fall" may be
upward or downward or sideways; the direction does not matter, as long
as it is free and unrestrained.

Plate 21.  Preparing Vostok I for Yuri Gagarin's orbital flight.

American Tnstitute of Aeronautics and Astronautics, Inc.

This is why one can feel weightless even in the presence of gravity.  A
man in free orbit around one of those dense dwarf stars whose
gravitational field is a million times as great as Earth's would still
feel completely weightless.

And, conversely, one can feel "weight" even if there is no gravity;
acceleration can produce an identical effect.  If you were standing on
those bathroom scales out in deep space, billions of miles from any
celestial body, they would again register zero weight.  But attach a
rocket motor and start it firing-then weight would return.  At an
acceleration of 32 feet per second per second the scales would read
correctly: you would be under "I g," and unless you had some other
means of discovering the truth, there would be no way of telling that
you were not standing on the surface of the

Earth.  The absolute equivalence of weight due to gravity and that due
to accelerations is one of the cornerstones of Einstein's General
Theory of

Relativity.  As we shall see in the next chapter, it also provides us
with a means of generating weight artificially, should that be
desired.

When Sputnik 2 launched the dog Laika into orbit, the experiment proved
two things.  It demonstrated that higher animals (presumably including
man) could endure long periods of weightlessness, and it showed that
the Soviet

Union was intensely interested in space travel, not only space
science.

Later experiments, in which dogs were safely reco,~ered after several
days in orbit, gave the Soviet

Union further valuable information, but it was generally believed that
the first manned flights would be fairly brief suborbital or ballistic
shots, like those with which the United States did in fact open its own
program (Shepard, Grissom, 1961).  Hence it was a great surprise to
most people when the Soviets went straight for orbit on April 12, 1961,
and Yuri Gagarin circled the world in 89 minutes aboard Vostok 1. There
were men still alive who had been born when Jules Verne had dared to
suggest that this feat might be accomplished in eighty days, and
millions who could well recall when it was first done in as many hours.
*

From the opening of the Space Age to the first man in orbit was only
3,12' years-largely because the Soviets had made their very first
ventures into this new ocean with boosters already large enough to
carry a man, and merely had to develop the life-support systems.  The
United States not only had to do this but also had to stretch its
existing rockets to perform a task for which they had never been
designed.  By brilliant improvisation, the Atlas ICBM was upgraded and
"man-rated," so that less than a year after

Gagarin, John Glenn was able to perform three orbits of the Earth in
the

Project Mercury capsule Friendship 7 (February 20, 1962).

The four Mercury flights were followed by the still more successful
Gemini launches, ten in all, each involving two astronauts.  The Vostok
was succeeded by Voshkod, carrying as many as three men.  During the
first five years of manned space flight (1961-66) a truly extraordinary
record of achievement and safety was established, neither the Americans
nor the

Soviets (contrary to numerous reports) suffering any casualties.  By a
sad coincidence, the first fatalities in both space programs occurred
within a few weeks of each other during tests of the third generation
of manned vehicles (Apollo and Soyuz).  And in each case, the disasters
occurred virtually at ground level, not in space-which remains the
safest medium for transportation yet discovered.

A list of the outstanding events in this first half decade of manned
space flight (page 137) gives a good idea of

In Profiles of the Future I have given reasons for doubting if this
will ever be done in eighty seconds, though it may ultimately be
achieved in about one-eighth of a second.  That "ultimately" is quite a
long way off.

the remarkable rate of progress.  The nationalities involved have been
carefully omitted; if any reader finds it hard to remember who did
what, it may occur to him that, perhaps, it may not be as important as
he had imagined.

DATE ACHIEVEMENT

April 12, 1961 First man orbits Earth

August 6-7, 1961 First man spends full day in orbit

August 11-15, 1962 First launch of two spacecraft; first
near-rendezvous

October 12, 1964 First multi manned (3) spacecraft; first
"shirt-sleeve" (no spacesuits) environment; first non astronaut
passenger

March 18, 1965 First man to leave spacecraft in orbit

March 23, 1965 First manned orbital maneuver

June 3-7, 1965 First manned propulsion outside spacecraft

August 21-29, 1965 First men spend week in orbit

December 4-18, 1965 First men spend two weeks in orbit; first sustained
space rendezvous

March 16, 1966 First docking of two spacecraft

December 24-25, 1968 First manned voyage in orbit around

Moon

July 20, 1969 First men land on Moon

Since a lunar round trip takes less than two weeks, this series of
flights proved that there were no outstanding physiological barriers
between Earth and Moon.  Although numerous minor problems and
difficulties had been encountered, these had all been overcome, and it
seemed that man could do anything that be wished in space.  Adaptation
to weightlessness had been astonishingly easy; although it caused
housekeeping and, above all, sanitary annoyances, most astronauts found
it a delightful experience, and some were afraid that they might become
addicted to it.  Myriads of skindivers had known this for years.

However, it is important to realize that although weight

* To the invariable question "How do they MRnage?"  the answer is "Not
very well."  At least one American astronaut had a rather damp Right.
The ultimate solution to this problem is given in the next chapter.

Plate 22.  Vostok 1.

Novosti Press Agency

Plate 23.  Vostok I after atmospheric re-entry.

Novosfi Press Agency is nonexistent in orbit, mass or inertia remains
quite unaffected.  It is just as difficult to set a given object in
motion aboard a spaceship as it is on Earth, and it requires just as
much effort to stop it again.  The inherent laziness of matter-its
tendency to keep on doing the same thing-is independent of gravity.
Although this fact can be used to advantage, it can also cause
problems.

Astronauts engaged on the early extravehicular activities found it very
difficult to control their movements, because these continued even
after the initial force was applied.  Hampered as they were by their
clumsy pressure suits, they found even the simplest tasks exhausting;
they needed both hands merely to keep themselves in position.  However,
by the time the

Gemini series of flights had terminated, suitable constraints, tethers,
and handrails had been tested, and the astronauts were able to carry
out all their assigned tasks without difficulty.

What is perhaps surprising is that a man can step out of a vehicle
hundreds of miles above the Earth and drift along beside it for.  hours
without any sense of vertigo or disorientation.  It is true that all
those who have experienced this have been highly selected, trained, and
motivated; it may well be doubted that the average person would enjoy
it.  But once again the adaptability of the human organism may astonish
us; in view of the universal fear of heights, who would have believed a
century ago that flight would be possible for almost everybody?

There was never any doubt that the other problems of maintaining life
in space could be solved by straightforward engineering techniques.
What made the building of "Life Support Systems" very difficult in
practice were the contradictory requirements of extreme reliability and
minimum weight; the

Mercury capsule, in particular, was a tour de force of expensive
engineering.  Everything, including a heavy heat shield, had to be
included in the 3,000-pound payload which was the maximum that the
Atlas could inject into orbit.  The much more powerful Titan booster
used for the Gemini flights could orbit 8,000 pounds, but even this was
little enough to keep two men comfortable in space for fourteen days.
By contrast, Gagarin's

Vostok weighed 10,000 pounds, and the three manned Vosbkod more than
12,000, so from the very beginning the Soviet Union was operating under
much less severe weight restrictions.

This reflected itself in many details of design.  For example, the
Soviet space capsules had sufficient braking ability to touch down
softly on land, with their crews inside (though the astronauts landed
separately on the earlier flights).  The American spacecraft had to
splash down at sea, with all the resulting complications, expense,
operational restraints, and possible dangers of a mid-ocean recovery.
And perhaps even more important, the cabin atmosphere in the Soviet
spacecraft was normal air, whereas to save weight and reduce
complexity, the American designers elected to use pure oxygen.  There
was nothing wrong with this decision per se, but by a series of
disastrous errors and oversights it led to the loss of three lives,
tens of millions of dollars, numerous reputations, and perhaps a year
of time on the journey to the Moon.

The air we breathe is normally under a pressure of slightly less than
15 pounds per square inch, and one-fifth of it consists of oxygen; the
remaining four-fifths is nitrogen (with a trace of other gases) and
plays no part in respiration.

From the physiological point of view, therefore, a pure oxygen
atmosphere at three-pounds-per-square-inch pressure is just as good as
air (one-fifth oxygen) at five times that pressure.  From the
engineering point of view it has several advantages: the risk of leaks
is smaller, the pressure cabin need not be so strong, extravehicular
activities are easier, and the whole air-purification' system is
simplified.  The fact that in the 1967 Apollo disaster the capsule
under test contained (a) pure oxygen at full sea-level pressure (and a
little more); (b) inflammable substances that had accumulated
unnoticed, and (c) electrical equipment that may have been faulty, does
not mean that there was anything basically wrong with the design.

Under normal conditions a man uses about two pounds of oxygen per day-a
surprisingly small quantity-which presents no storage problems for
flights of a few days or even a few weeks.  After the "combustion" of
the food which provides the human machine with energy, the gaseous
exhaust products are carbon dioxide and water vapor; these must be
continuously removed, otherwise the atmosphere will quickly become
unbreathable.  Various types of

CO, absorber and water separator have been available for decades,
largely as a result of submarine technology, though they have had to be
carefully redesigned to work in the weightless condition.  In
principle, oxygen can be regenerated from the carbon-dioxide absorber,
but the additional complications are not worth it except for the very
long-duration missions involved in planetary flights or permanent space
stations.

A man requires even less food than oxygen-about 13% pounds per day for
a 3,000-calorie diet.  But this is the dry weight, assuming that it is
completely dehydrated, as is the case with the freeze-dried foods used
on the Gemini and Apollo missions.  An astronaut also needs 5 to 6
pounds of water for drinking and for reconstituting the food.

However, the water problem is much simpler than the oxygen one, for it
is easily extracted from the atmosphere, purified, and reused.  In
addition, the electrical generating system of fuel cells used on both
Gemini and

Apollo actually produces water as the reaction proceeds, so ample
supplies are available for both consumption and toilet purposes.

The temperature of a spacecraft has to be regulated very accurately,
for though men can survive for limited times over an extraordinary
range (from above boiling

'point in very dry air, down to far below freezing), for optimum
working conditions the cabin temperature should not stray outside 70-80
degrees

Fahrenheit.  In order to keep within these limits, a manned spacecraft
usually has to be cooled.

This will come as a great surprise to those who have heard about the
"intense cold" of outer space.  But temperature, like color, is a
property of matter; as space is a vacuum, it can be neither hot nor
cold.  Only an object in space can have any temperature, and the value
of this will depend in a rather complicated way on the beat falling
upon it from an outside source (usually the Sun, but possibly a nearby
planet), its own rate of radiation into space, and any internal sources
of beat (electrical, metabolic) it may possess.

A large manned spacecraft may generate many kilowatts of heat from its
equipment and the bodies of its crew.  (One kilowatt is the power of
the average portable electric beater.) If this were all trapped by an
efficient insulating system, neither machines nor men could survive for
more than a very few hours.  The excess heat has therefore to be
radiated away into space by suitable cooling fins or surfaces.  At the
same time, it is just as essential to see that too much is not radiated
away.  The cooling fins or surfaces.  At the same time, it is just as
anyone who has stood under a clear sky on a still winter's night can
testify.  If the spacecraft's radiating system is too good, the
temperature inside will start beading for absolute zero (-460 degrees
Fahrenheit).  It won't get there, of course; whether it levels off at
minus 300 or only minus 100 depends partly on the vehicle's location.

If the spacecraft is in full sunlight, every square yard facing the Sun
will receive almost 1132' kilowatts of solar heat, and it may easily
get too warm.  If it is in shadow on the night side of Earth, for
example-it will be shielded from this intense source of heat and will
tend to get too cold.

It must therefore have some way of adjusting its radiation to varying
conditions, and this can be done by opening and closing reflecting
screens.

The fact that this problem has been already solved for the worst
possible case-a close satellite that swings from midnight to midday
every forty-five minutes-proves that this matter is fully under
control.

A much more difficult heating problem is that encountered in
re-entering the atmosphere; for a long time it was not even certain if
this could be solved.  The energy of a body moving at orbital speed is
enormous; anyone who has picked up a rifle bullet immediately after it
has bit a target will know that it is uncomfortably hot, and an object
traveling at 18,000 miles an hour has at least thirty times as much
energy.  There is, in fact, no substance which would not be completely
vaporized if all its orbital energy were converted into heat.  This
problem had to be solved as part of the ICBM program; if missile nose
cones could not be brought safely back into the atmosphere, there
seemed little hope that fragile human cargoes could survive the same
treatment.

The answer was found in 1952 by H. J. Allen, chief of the high-speed
research division of the Ames Aeronautical Laboratory.  For almost half
a century aircraft had been growing slimmer and more streamlined, and
it seemed logical to assume that this process would continue as even
greater speeds were attained.  But this was a case where intuition, and
even advanced mathematics, was completely misleading.  At the hyper
sonic velocities of re-entry, where temperatures of up to 12,000
degrees

Fahrenheit were encountered, all the needle-nosed models melted down
within seconds.

Allen realized that the opposite approach was needed.  By using a blunt
body-the very reverse of streamlined-a powerful shock wave would be
produced ahead of the missile, and most of the frictional heat would be
carried off in a sheath of incandescent air; only a small fraction.
would leak back into the capsule itself.  So evolved the inelegant,
approximately conical shape first made famous by the Mercury vehicles;
the Soviets, presumably using similar arguments, chose a completely
spherical design, so that Gagarin flew around the world in a giant
cannonball that might have come straight out of Jules Verne's novels.

Curiously enough, nature had given a hint that flattened, rounded
shapes would best survive re-entry.  The small, glassy meteorites known
as tektites often assume this form, as they are fused and molded by
their passage through the upper atmosphere.  The importance of this
minor astronomical curiosity, which might have saved the United States
a few hundred million dollars had it been realized earlier, was first
noticed by the meteorite expert H. H. Nininger, at the very moment that
Allen was circu

I" e THE PROMISE OF SPACE

la ting his highly secret findings to & skeptical missile makers.  *

Even with the blunt-nosed configuration, enough beat would reach the
forward part of the spacecraft to produce temperatures of several
thousand degrees, and it was therefore necessary to Provide additional
protection.

After experiments with various alternative systems, a saucer shaped
plastic and fiberglass "ablation shield" was developed, which slowly
burned or charred away during re-entry.  Millions of Americans will
remember the alarm felt during John Glenn's three-orbit flight, when a
faulty indicator lamp suggested that his heat shield had come adrift.
If this had really been the case, nothing could have saved him from a
meteoric fate.

In the decades before man went into space, there was much concern over
the human body's ability to withstand the accelerations involved.
However, space travel does not necessarily demand high acceleration;
the time will come, though perhaps not in this century, when it will
cause no more physical stress than the takeoff of a jet airliner.  But
for the reasons given in Chapter 7 fuel economy requires that today's
rocket vehicles perform their task as quickly as structural
considerations allow,f and this involves peak accelerations (at the
moment before engine cutoff, when the propellant tanks are almost
empty) of up to eight gravities.  Even higher accelerations are
encountered during the return through the atmosphere, when up to 12 g
may be experienced briefly.  (At 12 g, a 170-pound man weighs one ton.)
But thanks to form-fitting couches and prior training, the astronauts
felt little more than momentary discomfort; they were even able to
continue talking while their apparent weight increased almost tenfold
and their blood became as dense as molten metal.

Anyone who has ever witnessed the takeoff of a large launch vehicle
will have marveled that a human being can survive even within several
hundred yards of such a con * The problems of the needle-nosed re-entry
vehicle have now been solved, and it is now used in certain
applications, especially for warheads designed to frustrate antimissile
missiles.  t Ideally, a rocket should take off from the launch pad at
the highest possible acceleration.  The huge propellant tanks, however,
would become impracticably massive and heavy if they had to withstand
accelerations of several gravities when full.  It turns out, after all
the calculations ("optimization studies") are made, that for a large
liquid-propellant rocket the best compromise involves a lift-off at the
surprisingly low acceleration of about one-fourth of one gravity.

tinuous concussion; the unimaginable volume of sheer sound produced by
a multimillon-horsepower rocket engine is not even faintly conveyed by
radio or TV.  But this, too, has proved to be little problem to the
astronauts in their double-walled, insulated capsules.  Rockets, like
jets, leave most of their noise behind them.  Though they may disturb
whole countries, they do not inconvenience their passengers.

Apart from weightlessness, the greatest unknown hazards of space in the
days before men entered it were meteoroids and radiation.  There had
been many conflicting estimates of their possible dangers, and much of
the early experimental work with space probes was devoted to resolving
these.

Meteoroids come in all sizes, from barely visible specks of dust to
giant boulders, or even small mountains like the object which produced
the famous

Arizona meteor crater.  They move at velocities of anything from 7 to
40 miles per second with respect to the Earth, depending upon whether
they are overtaking it or meeting it head-on.  Needless to say, there
is no hope of providing protection against the larger varieties; the
only safety lies in statistics.  Fortunately, those statistics are
quite reassuring.

A meteroid weighing as much as one ounce is exceedingly rare: 100
square feet of spaceship would experience an impact with such a giant
about once every million days, or three thousand years.  The numbers
rise rapidly as the size of the particles decreases; for a 1/ 100-ounce
meteroid, the waiting period between impacts would be only about three
years, but an object as small as this presents little danger to the
hull of a spacecraft.

The best proof of the relative harmlessness of meteoroids is the
millions of hours of successful operation that robot probes some with
extremely fragile structures-have now accumulated beyond the
atmosphere.

Meteoroids may be a nuisance-nota danger-to windows and optical
elements (especially telescope mirrors) in space; they may eventually
produce a kind of sandblasting effect which could degrade performance.
Additional protection for critical areas may be needed on very long
voyages, especially through the asteroid belt between Mars and Jupiter,
where there seems to be a great deal of space junk.  And they may be a
slight hazard to men wearing spacesuits, which naturally cannot provide
as great a safety margin as the metal hull of a spaceship.

Even on those rare occasions when one of these cosmic bullets does
penetrate the wall of a spacecraft, the damage is not likely to be
serious; in most cases the small hole produced would merely add to the
existing inevitable air leakage and could be easily sealed.
(Self-sealing materials, like those used in aircraft fuel tanks, could
be employed if necessary.)

Even if the hull damage were quite serious but short of
catastrophic-there would normally be ample time for the crew to put on
spacesuits and then set about repair and re pressurization  It takes
many minutes for all the atmosphere of a space cabin to escape, even
through quite a large hole.

This seems a good point to deal with one of the most persistent myths
of the Space Age-the almost universally held idea that exposure to
vacuum would not only be instantly fatal, but could result in the
victim exploding because of internal pressure.  There was never any
reason for believing this, and it has now been disproved
experimentally.  Dogs and chimpanzees have survived vacuum for
astonishing lengths of time-up to 3 minutes-with no permanent ill
effects, though they normally lose consciousness after about 15
seconds.  A man who was psychologically and physiologically prepared
for the experience (which does not even seem painful, though it is
probably uncomfortable) would have at least a quarter of a minute of
useful consciousness-a great deal of time in an emergency.  And even
after he had lost consciousness, he would recover if he could be
repressurized within one or two minutes.

The human body is a tough piece of engineering, and, as every skindiver
knows, all its internal airspaces open into the surrounding medium so
that pressure quickly equalizes.  Swimming upward 10 feet, which takes
only a few seconds, produces the same drop in pressure as opening an
Apollo capsule to the vacuum of space.

The remaining hazard-radiation-has also turned out to be not so serious
as was once feared, although the discovery of the Van Allen belt caused
a momentary flurry of alarm.  Beneath these zones of trapped radiation,
astronauts can orbit for months without risk, and all long range space
missions will pass through the belts so swiftly that they can be
ignored.

The real radiation danger may be the Sun-especially around its 11-year
peaks of maximum activity, one of which coincides with the first Apollo
flights.  Several times a year, tremendous eruptions known as "flares"
occur on the surface of the Sun, and these spray high-speed, charged
particles (mainly the nuclei of hydrogen atoms) throughout the Solar

System.  It is possible to provide some shielding against these, at
least for short journeys like the flight to the Moon.  On longer
missions, such as voyages to Venus or Mars, the situation may be more
serious, and spaceships may have to be provided with a special "storm
cellar" for protection against the occassional but possible lethal
solar outbursts.  Even this is not certain, and judging by the way in
which all the other space bogeys have evaporated, no one will be
surprised if solar flares also turn out to be more spectacular than
dangerous.

Dr.  Charles Stark Draper, president of the International Academy of

Astronautics and head of the MIT.  Instrumentation Laboratory, which
developed the Apollo guidance system, once made the rather startling
remark, "Space is a benign environment."  It is beginning to appear
that this is indeed the case.  Certainly it is not so implacably,
relentlessly hostile as the Antarctic or the ocean depths.  It presents
problems, as does all new territory, and we have to proceed with
caution as we move into it.

But it also presents tremendous opportunities which we now have the
skill to exploit.

We are like seamen who have just landed on the coast of a new
and-perhaps-empty continent.  On our first brief forays into the
interior we move in a spirit of mingled excitement and fear.  But we
are learning fast; and the time may come when our descendants in this
new land will far outnumber our ancestors in the old.

ISLANDS IN THE SKY

The space station, or permanent manned orbiting structure, may be
regarded as the next step beyond the brief extra-atmospheric excursions
which opened the Space Age.  A great deal of study and thought has been
devoted to the project, which has a literature going back at least
fifty years.  In fact, if one stretches a point, Hale's 1869 "Brick
Moon" must be classed as a true space station, since it was inhabited,
albeit involuntarily.

The whole subject of space stations raises once again the question:
"What can men do in space better than machines?"  This is more of a
philosophical than a technical problem, and we shall return to it later
in this book; for the moment, let us say that the question should
really be framed: "What can space stations do for men?"  It is already
obvious that they can do a very great deal indeed.

Many, though no tall of the applications satellites described in
Chapter 10 could perform their functions better if they formed part of
a manned complex.  A good example is provia6d by the meteorological
satellites.

Though these have transmitted enormous quantities of information to
Earth, this is only a tiny fraction of that available even to the
unaided human eye.  This is dramatically shown if one compares the
superb, full-color photographs taken on the later Gemini flights with
the best TV pictures from Nimbus or ESSA.  Moreover, this is only part
of the story.  The robot automatic systems are unselective and often
transmit virtually the same information over and over again.  A human
observer, especially one who was a trained meteor148

ologist, could concentrate on areas of particular interest, focus
special instruments on them, and ignore those that were not important.
Although this sort of thing could, in principle, be done with robot
systems, there comes a point when it is cheaper and more effective to
have the decision-making computer (i.e."  the man) on the s~of, and not
at the far end of an expensive communications link which cannot handle
full-color video signals in real time.

The meteorologists are still debating this point, but the military have
already decided; in 1965 the United States Air Force was given
authority to proceed with a Manned Orbiting Laboratory (MOL).  A veil
of secrecy promptly descended (or ascended?) over the subject, but a
good deal has been published about similar schemes, such as the Manned
Orbiting Research

Laboratory (MORL) and the Orbital Workshop-both NASA projects.

The earliest space stations, like the MOL (a 25-footlong cylinder
weighing about 15,000 pounds), would be launched into orbit as a single
unit; more ambitious ones would be built up section by section, until
ultimately they became virtual space cities.  They would be supplied
with essential materials by a shuttle service from Earth but would be
largely self-sufficient as far as oxygen and water were concerned, for
they would purify both in a closed cycle system.  Eventually they would
be able to provide their own food (or the bulk of it), through either
compact hydroponic farming systems or chemical synthesis.

Most designs for space stations envisage disk- or wheel shaped
structures, slowly revolving like giant carousels.  This rotation would
generate centrifugal force, and so give the station a kind of
artificial gravity.

"Up" would be toward the axis, "down" away from it, and the sensation
of weight would slowly ebb as one moved toward the center, becoming
zero at the axis.  A wheel 600 feet in diameter has to make three
revolutions a minute to produce a force equal to normal earth weight (I
g) at its rim.

Smaller structures spinning more rapidly would give the same result but
might cause vertigo and difficulties with scientific experiments.
Probably a fraction of a gravity-say, one-fourth-would be quite
adequate for most purposes.  It would permit almost normal walking and
would remove most of the housekeeping problems, especially the sanitary
ones.

Service vehicles would have to approach such a station along its axis
and match its spin before they docked to it; alternatively, there might
be a docking section which could be given a spin exactly countering the
station's, so that it was motionless with respect to any approaching
vehicle.  Yet another idea is that space stations might be built in two
or more sections, not necessarily in physical contact.  Only the part
where the crew ate, relaxed, and slept might have rotational gravity.
With all these possibilities, it is no wonder that many thousands of
man-hours of amateur and professional engineering skill have been
devoted to space-station design (see Plate 24).  The moment of truth is
now approaching, when we shall learn which of these actually work.

Launch vehicles of the Titan 3 C and Saturn 1 B class can place
payloads of 10 to 15 tons in close Earth orbit; the giant Saturn 5
developed for the

Apollo program can orbit no less than 120 tons.  What is more, the
propellant tanks of the last stages will also go into orbit with the
payload, and some of these have the cubic capacity of a large house.
With the addition of an airlock and a lifesupport system, they can be
fairly readily turned into shirtsleeve environments where men can work
without having to wear pressure suits.  Near-space will soon be full of
large, empty tanks which can be rather easily converted into desirable
orbiting residences, so its population may increase rapidly.

The uses of space stations may be purely scientific, "practical"
(including commercial), or military.  As far as the last category is
concerned, the

Space Treaty approved by the UN General Assembly on December 15, 1966,
has set certain limitations on what may now be legally done; in
particular, "nuclear weapons or any other kinds of weapons of mass
destruction" must not be placed in orbit.  This would seem to restrict
the use of military space stations to large defensive roles, i.e."
reconnaissance, communications, and perhaps missile interception.
Looking some distance into the future, it has been suggested that the
only effective missile defense will be based upon radiation weapons,
probably laser heat, rays or beams of charged particles.  Such weapons
could be employed only outside the atmosphere, which would absorb most
of their energy and limit their range.

The technical problems involved in generating and beaming the
quantities of power involved are gigantic but not insoluble.  However,
by the time we

Plate 24.  Space atation.  Drawing by R. A. Smith are able to build
death-ray-wielding orbital fortresses, missiles will be obsolete.  The
defense will be deadlier than the weapon it was designed to counter.

To turn to more cheerful and constructive subjects, manned laboratories
and observatories in space open up new horizons.  for knowledge such as
have not been glimpsed since the invention of the telescope itself.
What the unmanned automatic satellites have gleaned on the other side
of the atmospheric curtain is impressive enough, and they will continue
to gather immense quantities of data, often from places where it w;uld
be extremely unhealthy for human beings to go.  But manned activities
can produce results of a wholly new order; anyone who thinks otherwise
may try to imagine how fast the physical sciences would have progressed
if all experimentation and observation had to be done via
remote-controlled handling devices and TV screens.  Even the simplest
piece of scientific equipment requires innumerable adjustments, and
this is particularly true of new and untried apparatus designed to
extend the frontiers of knowledge.  The fully automated physics
laboratory or astronomical observatory is a nightmare to contemplate,
as the expensive failure of the first robot OAO (Orbiting

Astronomical Observatory) may remind us.

Since the early part of this century astronomers have made heroic
efforts to improve seeing by building their observatories on
mountaintops, but even here the problem is merely reduced, not
abolished.  Only on very rare occasions, for a few seconds at a time,
can the world's great telescopes be used at even one-tenth their
theoretical magnifying power.  For many purposes (such as photographing
faint galaxies), this is nota very serious limitation; but for
observing fine detail on planets or resolving crowded star fields, it
is a crippling one.  The images are smeared and scrambled by their
passage through the last few miles of atmosphere, and increasing the
magnifying power of the instrument only makes matters worse-like
looking at a newspaper block under a magnifying glass.  Some
ground-based astronomers of the past who have spent their entire
working lives studying the Moon and planets probably saw them with real
clarity for a total time that could be measured in minutes-spread over
half a century.

Yet, above the atmosphere, not only are seeing conditions always
perfect, but the completely blocked X-ray, ultraviolet, and infrared
bands of the spectrum, crammed with undiscovered secrets, are waiting
to be explored.  Because it spans an enormously greater range of
frequencies (see Figure 15), the far-ultraviolet band many contain
hundreds of times as much information as visible light.

The word "information" is used in the perfectly general sense; it does
not imply intelligent signals (though it certainly does not exclude
them).  In the astronomical field it usually means spectral lines,
which to the skilled interpreter speak whole volumes about stellar
compositions, velocities, temperatures, and the types of nuclear
reaction that power the stars.  No wonder, therefore, that astronomers
have long felt frustrated because the atmospheric window slams shut on
the spectrum, just when it starts to become more informative.  Nor is
it surprising that one enthusiast for space observatories, Professor
Kopal of Manchester University, has stated that manned telescopes in
orbit may "cause our more fortunate descendants to relegate most of
what we have learned about the universe from observations at the
surface of the Earth into a crude pre-history."

There is still a friendly disagreement as to whether the best location
for future space telescopes is in Earth orbit or on the airless Moon.
Boib sites have great advantages, and both will ultimately be used, but
the lunar observatory is still several decades in the future.  Orbital
telescopes, on the other hand, could be operating in the early 1970's,
using the hardware developed for the Apollo project.  As part of the
"Apollo applications program," detailed engineering studies have
already been made to see how the hi nar landing vehicle (Chapter 15)
could be adapted as a mount for a telescope, so that instead of
descending to the Moon it could remain in orbit as a first-generation
astronomical observatory, able to outperform Mount Palomar.

Though it is quite impossible to eva lute the cost effectiveness of
pure research, Dr.  William Tifft, director of the Manned Space
Astronomy Branch (that title is a sign of the times) of the University
of Arizona's Steward

Observatory, has calculated that a 200-inch telescope in space could
collect information one thousand times as efficiently as a ground-based
one.  To put it in terms of hard cash: even if it cost $2 billion to
build an orbital 200incher, it would do the work of a hundred such
instru

IS4 9 THE PROMISE OF SPACE

ments at ground level costing $20 million each.  This argument must be
taken with a large grain of salt; for one thing, there would be no way
at present of handling such an avalanche of information.  But the main
thesis is valid, and the important thing to remember is that the space
telescope could do work utterly beyond the power of any number of
instruments at the bottom of our muddy, wavering atmosphere.

It could, for example, vastly multiply our knowledge of the other
planets, which would suddenly appear at least ten times closer and a
hundred times sharper.  Such increased knowledge is essential before we
embark on expensive planetary missions, either manned or unmanned.  It
would allow us, for the first time, to search for planets of other suns
with the hope of detecting at least Jupiter-sized companions of the
nearer stars.  And by peering many times further into extragalactic
space, it would throw new light-or, rather, much older light-on the
origin of the universe and the great questions of cosmology.

If this sort of knowledge seems somewhat theoretical, and perhaps not
worth the billions of dollars it will undoubtedly cost, it should be
remembered that astronomy has always been one of the cutting edges of
scientific progress.  "The universe is the great physics laboratory
where we have been able to study matter under conditions where it does
not exist on Earth; and from those studies have emerged not only new
insights but also new industries.

The stars can conduct experiments on a scale which we will not be able
to match for centuries; and the research possibilities of orbiting
space stations may keep us busy for most of those centuries.  For the
first time, we will have access to vacuum of unlimited extent, with all
that this implies to physics and electronics.  Our civilization is now
practically founded on electronics, and this in turn depends entirely
on vacuum technology.  The very low and very high temperatures that are
readily available in space will also make possible experiments that
cannot, or should not, be conducted on Earth.  Perhaps the final
breakthrough in thermonuclear power will be achieved a few hundred
miles out in space, where any unfortunate accidents will result in
nothing worse than a very temporary second sun,

But it is, of course, the unique zero-weight environment which makes
the orbital laboratory so attractive.  We will be able to study the
behavior of atomic and molecular, living and nonliving systems, under
conditions that can never be reproduced on Earth.  As a result, there
may be fundamental advances in our knowledge of those two most
intractable of all phenomena-gravity and time.  Anyone who bets on this
as a certainty would be foolish, but not as foolish as anyone who
thinks it unlikely.

No scientists have been more interested in weightlessness than the
biologists and doctors, and not only because of their natural concern
with astronaut safety.  The way in which living matter, at the cell
level and above, reacts to the apparent absence of gravity is certain
to give new insights into the nature of life.  On Earth the size of
most organisms is gravity-limited, or at least gravity-controlled; what
will happen when this factor is removed?  Will there be an explosion of
growth, so that we can produce giant amoebas, guinea pigs, or other
entertaining science-fiction monsters?  One form of uncontrolled cell
growth is cancer; anything we can learn about such a phenomenon is
obviously of the highest medical importance.  This should give pause to
those who are fond of suggesting cancer research as an alternative to
space exploration-as if money cut from one program is ever switched to
another.

The knowledge, instrumentation, and technology derived from space have
in fact already contributed to medicine, but the greatest advances may
come from a project which may still seem like fantasy~ the orbital
hospital.

Anyone who has ever suffered from bedsores will know what a boon a low-
or zero-gravity environment could be; and for serious burns or
postoperative therapy, it might make the difference between life and
death.  The last letter I ever received from one of the finest minds of
our century,

Professor J. B. S. Haldane, was written in severe discomfort after he
had been operated on for cancer; in it be remarked what a blessing a
space hospital would be to "millions of patients like myself."

There is also a possibility-wildly speculative, but this is a field
where the stakes are indeed high-that the expectation of life may be
increased' when the wear and tear of gravity is removed.  Whether this
discovery would be beneficial or otherwise is a good subject for
debate, but it is one that could hardly be ignored.

These last conjectures may seem absurd to those who still look on
manned space flight in terms of today's multimillion-dollar
productions.  But, as will be shown later, the cost and difficulty of
space travel will be reduced by orders of magnitude in the decades to
come, until it is eventually little more unusual-or more expensive-than
jet transportation.  Anyone who finds this hard to believe should
consider the fact that, just forty years after Lindbergh, twenty
thousand people were flying the Atlantic every day.

The development of efficient and reliable space transporters, which can
be used over and over again like' conventional aircraft, not dropped
into the ocean after every mission, will make space travel an
economically as well as scientifically sound proposition.  The orbital
hospital will be one of the first beneficiaries; so will the orbital
hotel, with its variable-gravity suites and its cylindrical swimming
pool.  In the spring of 1967 such a project was seriously presented at
the Dallas Symposium on the

Commercial Uses of Space; the speaker was one Barron Hiltofi, whose
name is not unknown to those seeking accommodation in the far places of
this planet.

Orbital hotels will be good fun, but orbital industries may be a much
more serious matter.  It is virtually certain that many types of
manufacturing will become simpler and cheaper in space, when advantage
is taken of the low pressures and, possibly, high radiation levels
available there.  And there may be many chemical and metalurgical.
processes which will be possible only under weightless conditions. What
they are, of course, we will not know until our orbital laboratories
discover them; this is one of the best reasons for their
construction.

One of the most important functions of manned space stations will be
the maintenance of the numerous scientific and applications satellites
in orbit around the Earth.  As more and more services-environmental
surveying, meteorology, navigation, communications-are lifted into the
sky, so we will depend to an ever-increasing extent upon satellite
facilities~.

Troubleshooting, replacing expendables like the propellants required
for station keeping, repair, and the installation of large and complex
antenna systems-all these will be done by service crews based upon
orbital depots, flying to their jobs in low-powered shuttle vehicles.
Since most of the applications satellites will probably be in the
synchronous orbit, 22,000 miles above the Earth, we may expect the
largest of the service stations to be there.  Luckily, the problem of
shielding from Van Allen radiation is not too serious at this
altitude.

Finally, let us look a little further into the future.  The large space
station is the ideal starting point both for robot probes and for
manned expeditions.  All equipment can be checked out, and even
assembled, in space, and when everything is ready the propulsion can be
switched on and escape velocity built up gradually.  (In orbit, a body
already has 70 per cent of escape speed, so only an additional 30 per
cent is required.) There are none of the dangers posed by a takeoff
from Earth-bad weather, an abort near ground level, the possibility of
falling onto an inhabited area.  A failure to depart from orbit would
mean delay but not disaster.

The great ports of the centuries to come will be in orbit, hundreds or
thousands of miles above the Earth; here we will see the full flowering
of the rendezvous techniques pioneered by the Gemini and Apollo
flights.

Today's missions will lead ultimately to fuel depots, repair and
maintenance facilities, traffic-control systems, navigation and
quarantine authorities-everything that has evolved for the needs of
terrestrial transportation, with a few extras appropriate to space.

Every age has its dreams, its symbols of romance.  Past generations
were moved by the graceful power of the great windjammers, by the
distant whistle of locomotives pounding through the night, by the
caravans leaving on the Golden Road to Samarkand, by quinqueremes of
Nineveh from distant

Ophir..  .. Our grandchildren will likewise have their
inspiration-among the equatorial stars.

They will be able to look up at the night sky and watch the stately
procession of the Ports of the Earth-the strange new harbors where the
ships of space make their planet falls and their departures.  Often,
one of these brightly orbiting stars will suddenly explode in a silent
concussion of light, and a fierce, tiny sun will draw slowly away from
it.  And they will know that some nuclear powered mariner has set forth
once more, on the ocean whose farther shore he can never reach.

III.  A R 0 UND THE MO ON

VOYAGERS TO THE MOON

We are very fortunate to have, so close at hand, such a large and
fascinating world as the Moon for our first target in space.  For
terres trials the nearest land is only a quarter of a million miles
away.

The inhabitants of Venus, in the unlikely event that they exist, have
to travel a hundred times that distance.

As we saw in Chapter 5, the problem of getting from the Earth to the
Moon is essentially that of climbing out of one gravitational crater
and descending into another.  Figure 6 shows this in a qualitative
manner; the table on page 162 gives the numerical values for the
mission.

If Figure 6 was modeled out of some smooth material, such as glass, a
ball bearing dropped into it could reproduce all the movements of a
space vehicle in the Earth Moon system.  For example, a rocket which
left Earth at escape velocity would lose speed-at first rapidly, later
very slowly-as it receded from Earth.  If it were aimed toward the
Moon, it would be barely moving as it "went over the hump"; thereafter,
however, it would gain, speed as it fell into the Moon's gravitational
crater, and in the absence of any corrective action it would crash
against the lunar surface at the escape velocity of 5,300 mph.

It is clear that the precise path to (or around) the Moon would depend
very critically upon the initial velocity and speed of projection.  A
direct hit is quite unlikely; what is much more probable is that any
unpowered space probe would gain speed, make a hairpin bend around the
Moon, and head off again in some other direction.  It could even

TABLE 4

THE EARTH-MOON MISSION

ESCAPE VELOCITY

DEPTH OF GRAVITATIONAL

CRATER, MILES NIP'MILES/SEC.

Earth 4,00024,8007

Moon 1805,300 1.5

do a figure eight and return to the vicinity of Earth, perhaps to
repeat the performance many times, unless it came close enough to
re-enter the atmosphere.

One thing that it could not do would be to become a satellite of the
Moon; it would always gain too much speed in its fall toward it to be
captured.

Only if, by rocket braking, its speed were reduced in the neighborhood
of the Moon could it become a lunar satellite.

It will also be seen that the duration of the journey will depend, in
an equally critical manner, on the initial speed.  A rocket that can
just make it-that can barely climb over the hump-will take about five
days for the trip But a very slight excess speed cuts the time down
rapidly, though this may not be a good idea if the extra velocity has
to be neutralized for a landing.  The very first object to make the
journey (Luna 2, September 12-13, 1959) took only 35 hours.

There is one respect in which Figure 6 does not reproduce the real
situation.  It is a static model, and the Moon is of course moving
around the Earth in a period of about 29 days.  This does not affect
the general argument given above, but the actual shape or trajectory of
the paths between Earth and Moon will be affected.  Even this could be
taken care of by a more complicated model made out of sheet rubber, in
which the little crater representing the Moon's field could be set
creeping around its orbit at an appropriate speed.

With this theoretical background, we are now in a better position to
understand the lunar explorations of the

0 As might be gathered from Figure 6, the velocity of a rocket that can
just reach the Moon is only about 200 mph short of the velocity of
escape.

From the energy viewpoint, the Moon's orbit is already 99 per cent of
the way to "infinity."

Voyagers To The Moon 0 163 Early Space Age.  The first attempt to
launch a payload to the Moon was made by the United States

Air Force on August 17, 1958, using a Thor-Able-1 booster, which
exploded soon after takeoff.  Another launch on October 11 was almost
successful; the 84-pound Pioneer I payload failed to reach escape
velocity by the maddeningly small margin of 2 per cent (570 mph).  The
launch vehicle still had ample fuel for the mission when the onboard
computer prematurely cut the engine.

At 98 per cent of escape velocity, Pioneer 1 was able to rise 70,000
miles before it crashed back to Earth, and it gathered valuable
information about the great radiation belt.  Though it did not reach
the Moon, it was the first scientific probe into deep space.  It may
not be easy t& recall that, in 1958, 70,000 miles still seemed an
enormous altitude.

A month later, Pioneer 2's last stage failed to ignite; on

December 6 Pioneer 3-the United States Army's entry to the race-just
failed to reach escape velocity and almost matched Pioneer I's
performance, rising 64,000 miles and a I gain sending back valuable
data on the radiation belt.

So, by a few hundred miles an hour, the United States lost the
opportunity of being first into the Solar System,* for on January 2,
1959, the Soviet

Union launched Luna 1, or "Mechta" ("dream"), on a trajectory that took
it within 5,000 miles of the Moon.  Its payload of no less than 795
pounds included instruments for analyzing cosmic rays, recording
meteoroids, and measuring the lunar magnetic field.

After swinging past the Moon (apparently it was not intended to make an
impact), Mechta had sufficient velocity to escape from both the
terrestrial and the lunar gravitational fields.  But it was still a
captive of the Sun, which it now circles in an orbit a little larger
than the Earth's.  It thus achieved not only the first lunar fly-by,
but became the first artificial planet, with a "year" of 443 days.

A similar feat was achieved only two months later by the United
States

Army's Pioneer 4 (March 3, 1959).

0 The first manmade objects ever to leave the Earth were small metal
pellets launched by an explosive charge on an Aerobee rocket 50 miles
above

New Mexico on October 16, 1957.  One of these artificial meteors
attained a speed of 33,000 mph-far in excess of escape velocity.  The
experiment was conceived by Professor Fritz Zwicky of the California
Institute of

Technology.

This, the first American space probe to escape from the Earth, passed
within 37,000 miles of the Moon and then went into a 407-day orbit
around the Sun.

None of these feats, however, was as dramatic as the first physical
contact with the Moon, achieved by Luna 2 on September 13, 1959, at
21:02:23

Universal Time.  After its 35-hour flight, the 860-pound instrument
package (and the empty 3,330-pound final-stage rocket) landed on the
great plain of

Mare Imbrium.  Like thousands of other amateur astronomers, I was
watching for the moment of impact, with my Questar aimed out over the
Indian Ocean at the setting Moon.  However, there is no conclusive
evidence that the event was observed-except by the radio telescopes
which recorded the change in pitch of the transmitter as it accelerated
in the Moon's gravity field, and the exact moment when its sudden
silence announced that the first man-made object had reached another
world.

Less than a month later, on October 4, 1959, Luna 3 revealed something
that had been bidden from the human race since the beginning of
history-the far side of the Moon.  Although the photographs radioed
back from its automatic darkroom were crude by later standards, they
showed hundreds of craters and hinted at subtle and still unexplained
differences between the two lunar hemispheres.

Luna 3, after looping around the Moon, shuttled back and forth between
the two gravitational fields for about six months, then re-entered the
Earth's atmosphere.  It had opened up a new era in astronomy, proving
that the time was coming when the smallest details of the most distant
planets would no longer be hidden.  Yet after this dramatic opening,
there was a pause of almost five years before the next advance in lunar
reconnaissance, and this only after a series of heartbreaking
failures.

This delay was partly due to concentration of efforts into other and
more rewarding missions-manned space flight, probes to Mars and Venus
(see

Chapter 21), and many other scientific and applications satellites.

Moreover, the rather poor quality of the Luna 3 pictures-which had even
provoked cries of "Fakel" from irresponsible or ignorant
journalists-showed that considerable improvements in technique were
still needed.

Luna 3 had taken photographs with a conventional camera system,
automatically processed them onboard,

then scanned them at leisure and radioed the images back to Earth. This
system has a number of advantages; the United States orbiter vehicles
also used essentially the same process when they completed the mapping
of "Farside" seven years later.  It permits working at low radio power
levels-the main consideration in the design of any space probe-because
the picture transmission can be spread over as long a time as is
necessary.

The jet Propulsion Laboratory's Ranger spacecraft, however, were
designed to use a real television system, though one limited to a
transmission rate of one frame every 2,12' seconds instead of the 25 or
30 frames per second of domestic television.  In this case there was no
alternative; the spacecraft were going to fly straight into the Moon
and would be destroyed on impact, so the pictures had to be sent back
as quickly as they were taken.

The first five Ranger shots (August, 1961-October, 1962) failed for a
variety of reasons, no tall connected with the spacecraft itself.
However,

Ranger 4 did reach the Moon on April 26, 1962, being the first American
spacecraft to do so.

Between Rangers 5 and 6 there was a pause of fifteen months, while
numerous scientific subcommittees tried to find what had gone wrong.
During this hiatus, the Soviet Union launched its fourth Luna, on April
2, 1963, but it too failed to achieve its objectives.  :

On January 30, 1964, the jet Propulsion Laboratory tried again with
Ranger 6. Everything went perfectly all the way to the Moon, until the
last fifteen minutes.  Then, when the TV cameras were switched on,
nothing happened.  Later it was decided that a power supply had
shorted, perhaps owing to the failure of an insulator costing a few
cents.  This was probably the lowest point in the history of the United
States space program since the explosion of Vanguard TV3 on December 6,
1957.

Six months later, after more agonizing reappraisals, JPL launched
Ranger 7; it is probably not too much to say that the future of the
entire laboratory was riding with this payload's six TV cameras.  This
time the years of effort and heartbreak were rewarded; the Atlas-Agena
launch vehicle worked perfectly, the trajectory was exactly as planned,
and when, seventeen minutes before the calculated moment of impact, the
cameras were switched on,

Plate 25.  Adjusting the antenna ol Ranger 2.

American Institute of Aeronautics and Astronautics, Inc.

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Plate 26.  Surveyor 3 model.

Hughes Aircraft COMPany signals started coming back at once.  Within
the next quarter of an hour the

Moon was brought a thousand times nearer to Earth than ever before. The
closest of the 4,316 high-quality photographs obtained showed crater
lets on the lunar surface only a few feet in diameter.  Until then the
best telescopes had been unable to resolve objects less than half a
mile across.

Ranger 7 had beaten the telescope by a greater factor than that
instrument had surpassed the unaided human eye.

Ranger 8 (launched February 17, 1965) performed even better than its
precursor, sending back 7,000 photographs during the fl nal 23 minutes
of its flight.  It seemed impossible that Ranger 9, the last of the
series, could top this; but it did so, little more than a month later,
on March 24, 1965.  This time the JPL scientists had devised an image
converter so that, as quickly as the pictures came back from the Moon,
they could be displayed on a TV screen.  These images were carried by
the national networks, and so, for the first time, millions of people
watched the Moon racing toward them, as it was actually happening.
Moreover, the impact point chosen was in dramatic, mountainous terrain,
not the rather flat and uninteresting "seas" which the previous
missions had reconnoitered as possible landing sites.

The target now was the 70-mile-diameter crater Alphonsus, chosen
because slight volcanic activity had been reported near its central
peak.

No one who watched the mountain walls of Alphonsus expanding second by
second and saw more and more details never before witnessed by human
eyes swimming into view is likely to forget that transmission, or the
sign that then appeared on the television screen for the first time in
history-LIVE

FROM THE MOON.

Almost as impressive as the photographic coverage obtained was the
amazing accuracy of these last Ranger shots.  When you next look at the
Moon, notice what a small object it appears to be, and remember that it
is actually over 2,000 miles in diameter.  Then consider that the last
four Rangers missed their nominal aiming points by these margins:

ACCURACY, MILES

Ranger 6 20

Ranger 7 10

Ranger 8 20

Ranger 9 3

Such remarkable performances are made possible by mid-course
corrections; when a spacecraft has been launched on its initial
trajectory, it is tracked for many hours by radio equipment which can
measure its position to within a few feet in range, even at the
distance of the Moon.  Velocity can be measured to a similar degree of
accuracy, and given this information, computers can predict the future
position of the spacecraft as it moves under the influence of gravity.
Sometimes the injection into orbit is so precise that no correction is
necessary, but normally a change of a few miles an hour is needed.  The
amount and direction of this impulse is calculated, the spacecraft is
reoriented and a brief burst of power applied from its control jets,
and tracking continues until the effectiveness of the correction can be
determined.  Naturally, a trifling alteration in velocity at mid-course
can produce a huge change at the end of a quarter-million-mile journey,
and the correction therefore has to be made with great care.  Sometimes
things can go badly wrong during this operation, as the Soviet
scientists found on June 11, 1965.

They were now going through much the same ordeal, though without the
glare of publicity, that JPL had endured between Rangers 1 and 7. Less
than two months after the last of the

Rangers had made its TV spectacular, the Soviet Union began a new
series of experiments, designed to achieve the most difficult yet most
significant of all space feats to date-a landing on the Moon.  All
earlier probes had crashed, un retarded into the lunar surface at over
5,000 mph.

Such was the fate of Luna 5 on May 12, 1965; its braking rockets failed
to operate properly, and it crashed into the Sea of Clouds.  A month
later-june 10-Luna 6 disgraced itself; when a course correction was
applied, the rocket engine refused to stop thrusting after the desired
impulse had been given.  It continued firing until it had exhausted its
fuel, and so Luna 6 missed the Moon by a little matter of 100,000
miles.

On October 8 Luna 7 did somewhat better; it reached the Moon, but its
retrorockets canceled only part of its speed, and it was destroyed on
impact.  Exactly the same thing happened to Luna 8 on December 7; as
some consolation, however, the Soviet Union achieved its second
photograph reconnaissance of the lunar Farside in 1965 from Zond 3, a
deep-space probe that then continued in orbit around the Sun.

By this time no one could doubt the determination of the Soviet space
scientists to achieve their goal of a lunar landing.  Sir Bernard
Love]], who had tracked all the Luna flights with the giant 250-foot
radio-telescope at Jodrell Bank, remarked after analyzing the maneuvers
of

Luna 8 that they "narrowly missed complete success.... They have
probably obtained a great deal of new information which will enable
them to correct the remaining minor faults."

However, some pessimists were beginning to fear that the trouble might
not be with the Lunas, but with the Moon itself.  They revived the old
theory-only slightly shaken by the Ranger photographs-that the Moon
might be covered by a deep layer of dust which could swallow any dec
ending spacecraft.  The persistent Soviets put this fear to rest on
February 2, 1966, when Luna 9 made a successful touchdown in the Ocean
of Storms.

The small, egg-shaped camera capsule was attached to a larger
rocket-propulsion unit, and the whole assembly, after it had been aimed
toward the Moon, was allowed to coast until it was within 50 miles of
the surface.  By this time it had been falling for hours through the
lunar gravitational field and had acquired a speed of more than 5,000
miles an hour.  In less than a minute it would impact on the Moon's
surface; it actually took the retrorockets 48 seconds to reduce its
speed to about 100 miles an hour at a very low altitude.  just before
landing, the camera capsule was detached from the propulsion unit and
fell separately some distance away.

It was not what a human astronaut would have called a good landing
("one you can walk away from"), but the instruments had been designed
to withstand the expected shock.  A few minutes later the capsule
opened up like a flower, unfolding four petals.  Its periscopic camera
lens started to survey the scene, and the first ground-eye view of the
Moon was radioed back to Earth.*

Since the camera was only two feet above the surface, the horizon was
very close-less than a mile away.  The view, in fact, was that which a
sitting man would have, and was limited by the steeply curving lunar
surface.  (From a given elevation, one can see only half as far on the
Moon as on Earth.)

But the pictures were excellent; Luna 9 had a full 360 degrees of
vision, and objects in the foreground only one-tenth of an inch across
could be resolved.

Luna 9 settled the question still left open by the Ranger series: the

Moon's surface, at least in one region, was made of some porous,
crunchy material and was firm enough to support a considerable weight.
The designers of the Apollo landing vehicle breathed a sigh of
relief.

On April 3, 1966, Luna 10 achieved a much easier, but still very
important, feat by becoming the first satellite of the Moon.  At the
appropriate point, its retrorockets reduced its speed from 4,700 to
2,800 mph, so that it could no longer escape from the Moon's
gravitational field.  Accordingly, it went into a 3-hour orbit, ranging
in height between 220 and 630 miles from the lunar surface.  During
several days of operation, before its batteries were exhausted, it
radioed back a vast amount of information concerning the environment
close to the Moon, in forma 0 To be released, not by the Soviets, but
by Jodrell Bank, via the London

Daily Express.  When the radio signals from Luna 9 were received by the
250-foot telescope, it was realized that they were in standard
picture-telegraphy code.  The Express, which may not he the best
newspaper in the world but is undoubtedly the most enterprising, rushed
a facsimile receiver to Jodrell Bank and thus made one of the most
remarkable scoops of the Space Age.

Voyagers To The Hoon 0 171 tion which cannot be gathered by impact
probes which pass through this region in a few minutes.

While all this had been going on, the United States was preparing for
similar exploits.  Its lunar-landing vehicles, the Surveyor series
(built by the Hughes Aircraft Company), had been delayed several years
owing to problems, and downright disasters, with the Centaur-Atlas
launch vehicle.

When the incredibly complex Surveyor I lifted from Cape Kennedy on May
30, 1966, it was the first flight of the space probe and the first
operational use of the liquid-bydrogen -fueled booster.  No one would
have given odds of better than one in ten for a successful mission.

In the event, everything worked with textbook precision.  The new
booster launched the spacecraft on an excellent trajectory; a small
course correction was made in flight, and Surveyor beaded straight
toward the

Moon.  About 1,000 miles up, the vehicle was oriented so that its
solid-propellant retrorocket pointed exactly along the flight path. Its
gyros kept it locked in this direction as it continued to gain speed,
and 200 miles above the Moon its radar was switched on by a signal from
Earth.

Thereafter it was controlled by its own electronic brain.  It continued
to fall until about 60 miles from the surface, at which point it had
reached a speed of 6,000 miles an hour.  The big retrorocket was then
fired; by the time it had burned out, 40 seconds later, Surveyor was
only 6 miles up and traveling at 250 miles an hour.

Now it was very much on its own, for it was impossible to provide
effective guidance from Earth.  Radio signals take 134' seconds to make
the journey from the Moon, so by the time any error had been noted and
a correcting signal sent from the JPL control room at Pasadena, there
would have been a delay of not less than 2,12' seconds.  Yet the
critical landing manueuvers had to be made instantly, during the final
stages of the descent.

For the last 6 miles, therefore, Surveyor eased itself down toward the
Moon on gentle blasts from three small liquid-fueled vernier
(fine-adjustment) rockets, under the control of a computer which was
kept informed of height and velocity by the onboard radar.  So well did
this work that the vehicle came to rest only 13 feet above the lunar
surface; it fell freely for this distance, equivalent to only 2 feet in
the Earth's gravitational field, and the shock

Plate 27.  Surveyor 5's photo at a lunar boulder, 1%6.

Hughes Aircraft Company

Plate 28.  Surveyor spacecraft.

Hughes Aircraft Company absorbing undercarriage easily neutralized the
slight impact.

Unlike Luna 9, Surveyor did not rely on batteries but carried solar
cells, generating electricity from sunlight; so it was able to transmit
thousands of superb photographs (some in color) before the Sun set and
the long lunar night began.  Even then, to everyone's surprise, it
survived the low temperatures and revived at dawn, giving the
experimenters an additional bonus.  The moonscape it viewed was similar
to that seen by Luna 9, 500 miles away; we will discuss the
interpretation of these remarkable photographs in Chapter 17.

On August 10, 1966, the United States began its third

Plate 29.  The 85-toot-diameter antenna used for tracking Surveyor I en
route to its soft landing on the Moon,

Plate 30.  Model of Lunar Orbiter.

American Institute of Aeronautics and Astronautics, Inc.

Plate 31.  The crescent Earth, see.  from the Moon by

Orbiter 1.

The Boeing CompanY

series of Moon-oriented experiments, with the launching of Lunar
Orbiter 1.

Unlike the Soviet Union's Luna 10, which carried only instruments,
Orbiter

I's mission was primarily photographic.  Its Kodak-designed automatic
darkroom could process a 200-foot roll of 70-mm film; after the images
had been fixed, they were scanned by a flying spot of light and the
resulting electrical impulses radioed back to the stations of NASA's
Deep Space Network in Australia, Spain, and California.

Despite minor technical troubles, Orbiter 1 functioned superbly,
producing the first high-definition pictures of the lunar Farside.  Its
most memorable achievement, however, was the wonderful study of the
crescent Earth banging low above the edge of the Moon (Plate 31).  For
many millions of terres trials their first glimpse of this photograph

Plate 32.  Earth photographed from a distance of 214,808 miles on
August 8, 1967, by Lunar Orbiter 5. India and Ceylon are visible
through light clouds near the center; the entire east coast ol Alrica
is shown from the Mediterranean to the Cape ol Good Hope; Italy,
Greece, Turkey, the Red Sea, the

Arabian Peninsula, the Persian Gulf, and the Black Sea all can be
seen.

The Boeing Company must have been the moment when the Earth really
became a planet.

Later Orbiters did even better, producing a portfolio of lunar
photographs that would have been beyond the wildest dreams of
astronomers only a few years before.  These studies included the
stunning low-angle shot of the crater Copernicus (Plate 33), which
almost every newspaper in the world carried on its front page and which
was widely heralded as the "Picture of the Century."  (Ironically
enough, this was an unplanned test shot made by

Orbiter

2).  These photographs were of great psychological as well as
scientific importance, for the Rangers, Lunas, and Surveyors had begun
to give the impression that the Moon was a somewhat dull, flat, and
uninteresting place.

But now the image was beginning to emerge of a world with landscapes as
dramatic as any on Earth-where, moreover, there might still be a
considerable amount of volcanic or other activity taking place.

When Luna 13 landed on the Moon on Christmas Eve, 1966, and Surveyor 3
made a slightly bouncy but safe touchdown on April 19, 1967, robots had
been installed on the Moon that could dig and pry into its surface,
which, rather surprisingly, turned out to be more like good honest dirt
than any substance that the theoreticians had predicted.  There was no
longer any question that men could walk safely there; and it was
becoming more and more certain that it would also be an interesting and
scientifically rewarding place to visit.

Which was indeed good news-since that visit was scheduled to take place
within less than five years.

THE BIRTH OF APOLLO

By the mid-1960's there were a number of rockets in existence which
could, if everything went well, land a man safely on the Moon.  But
this was all they could do; they could not possibly carry the
additional fuel for the return journey, even though it is very much
easier to escape from the Moon than from the Earth.

Indeed, for a long time it se med unlikely that any rocket, no matter
how large, could make the round trip if it were powered by chemical
propellants.  The calculations gave absurd answers-million-ton vehicles
to bring payloads of one pound back from the Moon, for example On such
a basis, manned expeditions were obviously quite impracticable.

Yet there was a way of avoiding these enormous ratios, and the
theoreticians of the 1920's and 1930's had clearly indicated it.  There
was no need to use a single rocket to go to the Moon and back; by
employing orbital techniques, the journey could be 'broken down into a
number of relatively easy stages, flown by vehicles of moderate size.

A favorite scheme was that of refueling in space.  A rocket would be
launched into a close orbit around the Earth, exhausting its supply of
propellants in the process.  Then "tanker" vehicles could rendezvous
with it and pump fuel aboard.  When this operation had been completed
-I am quoting an actual figure, worked out by a distinguished Canadian
astronomer and published in a lengthy mathematical paper in the

Philosophical Magazine for January, 1941.  which might take weeks, if
desired, since the orbit chosen would be a stable one-the spaceship'
would then be refueled, above the atmosphere, and already moving at 70
per cent of the speed necessary to escape from the Earth.  At the
appropriate time it could turn on its engines and inject itself into
the mission trajectory.

The first operation of this type was carried out, though in a slightly
different manner, during the Gemini 11 flight of September, 1966.  The
spacecraft docked with its Agena target vehicle at an altitude of 180
miles, and the Agena was then commanded to fire its unexpended fuel.
This extra kick boosted the Gemini to the then record-breaking altitude
of 850 miles.

Even without refueling, however, a rendezvous in space could much
improve the logistics of a mission.  For example, the spacecraft which
has to make the final landing back on Earth requires a heavy heat
shield and parachutes; why waste hundreds of tons of fuel carrying this
equipment all the way down to the surface of the Moon, only to lift it
back into space again?

The sensible thing to do would be to leave it in orbit around the
Earth, to be picked up on the homeward journey.

When these ideas are taken to their logical conclusion, it seems that a
lunar voyage could best be carried out using not one spacecraft, but
three.

Type A would be a short-range vehicle, possibly winged, which would
carry equipment from Earth to orbit, and return by atmospheric braking.
Type B would be similar, but without wings or streamlining, and more
lightly constructed; it would be designed to land on the Moon by a
rocket braking alone.  It might be carried up from Earth in a Type-A
ship or assembled in space.

Type C would be a true spaceship; it would never land on Moon or Earth,
but would shuttle payloads between them, making a rendezvous with Type
A or

Type B at destination-like an ocean liner being met by tugboats.  Since
each vehicle would be designed for its specific mission, it could be
highly efficient.  Thus only the Type A, which has to climb up to Earth
orbit, need have powerful motors and rugged construction.  The others
could be very lightly built and relatively low-powered.

The importance of orbital rendezvous and refueling techniques in
avoiding enormous takeoff weights was first realized by the Austrian
engineer Baron

Guido von

The Birth 0/ Apollo 0 183 Pirquet in 1928 and further developed by many
other writers on astronautics.  In January, 1949, H. E. Ross published
a paper ("Orbital Bases") in the

Journal of the British Interplanetary Society, pointing out the great
value of a rendezvous in orbit around the Moon; he suggested that a
lunar-bound spaceship, before landing, should leave the propellants for
the return journey circling the

Moon, ready to be picked up on the way home.  A few years later, when
discussing these ideas in The Exploration of

Space, I wrote this description of Plate 2, drawn by R. A. Smith; it is
interesting to compare it with the lunar modules of today: "When the
ship is on the Moon, the undercarriage would play the role of a
launching rack, holding the rocket in the required position for
takeoff.  It could, therefore, be left behind ... and so might be made
detachable.  However, this would be bad economics, because it would be
cheaper to bring it back than to carry a new set of landing gear from
the Earth when the ship was preparing for its next voyage."  It will be
noted that reusability was taken for granted; it never occurred to us
that multimillion-dollar vehicles would be used for a single mission
and then abandoned in space.  We were not that imaginative.

If human beings were logical entities, controlled by reason instead of
emotion, these or similar ideas would probably have been developed in
an orderly manner, rendezvous techniques would have been perfected, and
we would have been ready to land on the Moon sometime around the end of
the century.  But once again politics and astronautics combined with
results that no historian could ever have predicted.  On May 25, 1961,
President

Kennedy announced that a manned lunar landing "in this decade" was a
prime national objective of the United States.

The previous month Yuri Gagarin had been the first man to go into
orbit; that, as well as earlier Soviet space achievements, was still
rankling.  So was a debacle only one week later, and much nearer to
home, the ill-fated

Bay of Pigs adventure, America's answer to the Anglo-French Suez
shambles.

Only a person of extreme political naivete would imagine that there was
no connection between these events and the challenging goal which the
United

States had set itself.  Yet only cynics or fools could fail to be moved
by the eloquence of President Kennedy's message to Congress.

We have examined where we are strong and where we are not, where we may
succeed and where we may not.... Now is the time to take longer
strides-time for a great new American enterprise-time for this nation
to take a clearly leading role in space achievement, which in many ways
may hold the key to our future on Earth.... We have never made the
national decision or marshaled the national resources required for such
leadership.  We have never specified long-range goals on an urgent time
schedule, or managed our resources and our time so as to insure their
fulfillment..  .. For while we cannot guarantee that we shall one day
be first, we can guarantee that any failure to make this effort will
make us last..  .. I believe this nation should commit itself to
achieving the goal, before this decade is out, of landing a man on the
moon and returning him safely to the earth.  No single space project in
this period will be more impressive.  to mankind, or more important for
the long-range exploration of space; and none will be so difficult or
expensive to accomplish.

For some years NASA and its subcontractors had been conducting design
studies of a mar med lunar landing, which it was thought might take
place in the 1970's at the earliest.  Now these theoretical exercises
suddenly became of the utmost practical importance; they would be the
foundation of the greatest scientific and industrial effort in the
history of mankind.  The $2 billion Manhattan Project which produced
the atomic bomb was only a tenth-scale model of the Apollo Project.
Although the arguments for and against it would begin at once and would
slowly heat tip during the coming decade, the die had been cast.  The
verdict of history may well be that the

United States made the correct decision, even if from dubious
motives.

The political decisions having been made, some equally difficult
technical ones were nov necessary.  There were three basic ways of
achieving the lunar flight, and each had its advantages and
disadvantages.

First there was the direct, or brute-force, method.  Thanks to
improvements in propulsion systems and remarkable reductions in
structural weight, it now appeared that even the early space
enthusiasts had been too pessimistic.  It was, after all, possible to
build a single vehicle which could make the round trip to the Moon,
using conventional chemical fuels.

However, at takeoff from Earth it would have to weigh about 5,000
tons-forty times the size of any rocket then possessed by the United

States.

The Birth 0j Apollo 0 185

The second approach was to use some kind of rendezvous, in orbit around
the

Earth.  For example, the lunar spacecraft might be launched, and
unfueled by one booster, and a later flight could carry the propellants
for the mission-perhaps in a complete propulsion unit that could be
coupled to the orbiting lunar ship.  This would permit the use of very
much smaller boosters than the direct approach; instead of a single
5,000-ton rocket, two or more 1,000-tonners would be used.

For a number of reasons, and despite bitter protests from some
advisers, this apparently attractive approach was turned down.  At that
time no space rendezvous had been achieved and no one knew what the
difficulties would be in practice.  It is possible that the decision
might have been different, had the knowledge and experience of the
Gemini program been available, but that was still five years in the
future.

A compromise was therefore adopted, which would allow the mission to be
carried out by a single launch from Earth.  This could be done using a
vehicle in the 3,000-ton class, with one rendezvous in lunar orbit. The
main spacecraft would not descend to the Moon but would remain circling
it while two of its three-man crew visited the surface in a small
landing vehicle, which would be abandoned when it had completed its
mission

This scheme appeared to have a number of advantages, though there were
many who thought that if a rendezvous in space had to be made, it
should be done a couple of hundred miles above the Earth, rather than a
quarter of a million miles away in lunar orbit.  Against this, the LOR
protagonists argued that their scheme involved landing the minimum
amount of equipment on the Moon-probably the most difficult and
certainly the most expensive part of the operation.  Even if there were
a disaster during the landing or takeoff, the surviving astronaut could
bring the orbiting mother ship back to Earth.  And, finally, there was
no other way in -which the feat could be achieved with a

4 Credit for originating the concept of Lunar Orbit Rendezvous LORis
often given to Dr.  John C. Houbolt, then ( 1962) head of the
Theoretical

Mechanics Division of NASA's Langley Research Center.  The first
thorough analysis of the technique is certainly due to Dr.  Houbolt and
his colleagues.

single launch vehicle of reasonable size by the deadline set by the

President.  These arguments were accepted, and the Apollo Project was
committed to using Lunar Orbit Rendezvous.

THE VEHICLE

At the foot of the artificial mountain known as the Vehicle Assembly

Building there is a briefing room, one large wall of which is
completely covered with an immensely elaborate chart.  It must be the
most complex specimen of scientific graffiti in the world, and it
details all the thousands of separate operations that must be carried
out, in the correct order and at the correct time, so that three men
may make the round trip to the

Moon.  The planning behind that chart represents an investment of some
millions of man-years and some tens of billions of dollars.  We are a
long way indeed from the backyard spaceships built, with a little help
from their beautiful daughters, by the eccentric professors of early
science fiction.

Yet there is no need to go into this overwhelming degree of complexity
to understand the Apollo mission, which breaks down into a series of
consecutive, logical steps.  Most of the complication arises from the
need to anticipate, and to overcome, problems and emergencies that may
occur during the two-week, half-million-mile voyage.  The whole
operation has been planned so that, at any time, the mission may be
called off (aborted) and the men brought safely back to Earth.  The
road to the Moon is like a highway from which many side turnings branch
off at intervals, most of them leading back to the starting point.  We
will ignore all these detours (a few are, literal187

ly, dead ends) and concentrate only on the main highway the Nominal
(i.e., desired) Mission.

Let us start by looking at the payload which has to be dispatched
toward the Moon.  It consists of two separate vehicles, each a complete
little spaceship in itself-the Command Module (CM) and the Lunar Module
(LM).  The

Command Module is conical in shape, bearing a family resemblance to
the

Gemini and Mercury capsules; and like them, it is fitted with a
saucer-shaped heat shield for protection as it re-enters the
atmosphere-at 25,000 mph-on its return from the Moon.  For most of the
mission it is the home of the three-man crew, and it is the only part
of the huge

Apollo-Saturn 5 vehicle which survives the round voyage.

The Command Module has no propulsion system of its own, though it is
fitted with small control jets so that it can position itself at the
correct angle when it begins re-entry.  The rocket engine that will
send it homeward from the Moon, with its propellants, is housed in a
separate Service Module (SM)-a large cylinder upon which the Command
Module sits snugly, like the nose cap on an artillery shell.  The
Service Module also contains electrical power supplies and part of the
life-support system; its task is completed when it has brought the
Command Module back to the edge of the Earth's atmosphere, and it is
then jettisoned.

If only a lunar circumnavigation were intended without landing-these
two modules would suffice for the whole mission.  (In fact, if it were
not for food and air requirements, this combination would allow even a
trip around

Mars or Venus.) For the landing, the Lunar Module is carried, tucked
away in an adapter section immediately beneath the Service Module.  One
may liken its function, and indeed its initial location, to a dinghy
towed behind a cabin cruiser.  Thus the complete Apollo spacecraft
consists of the three units: Command Module, Service Module, Lunar
Module.  Their combined weight comes to almost fifty tons.

To launch fifty tons on an escape trajectory toward the Moon requires a
truly enormous rocket.  (It is worth remembering how huge the Atlas
once seemed-when it boosted the 1132' tons of the Mercury capsule to
only 70 per cent of escape velocity.) The vehicle designed for the task
is the Saturn 5, latest of the evolutionary line V-2 (Red

The Vehicle * 189 stone, Jupiter, Saturn 1).  Standing 280 feet high
(without its Apollo spacecraft payload, which adds another 80, to give
a total of 360 feet), the

Saturn vehicle weighs 3,000 tons.  This is almost all fuel and
oxidizer; the empty weight of the huge structure is little more than
200 tons.

It is all too easy to become numbed by statistics when contemplating
Saturn 5, but here is a modest figure that is nevertheless highly
impressive.  The vehicle carries more than thirteen times its empty
weight in propellants, despite the fact that two of these-liquid oxygen
and liquid hydrogen-require special insulation because of their
extremely low temperatures.

And to make matters worse, hydrogen also demands very large storage
tanks in proportion to its weight; it is the lightest liquid known,
with only one fourteenth of the density of water.

To lift this 3,000 tons of dead weight off the pad, the first stage
uses five rocket engines (hence the designation 5), each of a million
and a half pounds' thrust, giving a total thrust of 7,500,000 pounds,
or 3,750 tons.

The margin to produce lift is thus rather small, and the vehicle will
therefore rise quite slowly until it has lightened itself by burning
fuel.

It does this at the unbelievable rate of fifteen tons per second, and
this introduces another awesome statistic.  The pumps necessary to
drive such quantities of fuel and oxidizer into the giant combustion
chambers require turbines generating a total of 300,000 hp to drive
them; this is twice the engine power of the largest ocean liner.  There
are few other facts which demonstrate so conclusively the new order of
magnitudes involved in space transportation.  The giant engines that
propel the floating cities of the

North Atlantic could not even run the fuel pumps of the Saturn 5.

The nomenclature of the Apollo booster is somewhat confusing, as it is
derived from earlier vehicles in the Saturn program  There are three
stages, and it would be convenient if they were labeled S-1, S-2 and
S-3, or even A, B, and C. But for once the well-known Germanic sense of
order has been defeated (the whole Saturn program is managed by NASA's
Marshall

Space Flight Center, directed by Dr.  von Braun), and the final
configuration has turned out to be: SIC, S-11, and S-IVB.  We shall
just have to live with it.

The first (lowest) stage is the SIC, with its five enormous -*F- A 9
Adho I %MwL'4OA;& "Z.  OZ

Plate 34.  The Saturn.  5 space vehicle used in the Apollo missions.

North American Aviation, Inc.

Plate 35.  Sectional view of the Saturn 5 space vehicle.

North American Aviation, Inc.

mous 1,500,000-pound-thrust engines It is by far the largest element of
the whole assembly, containing 2,200 tons of propellants-a brand of
kerosene known as RP-I, specially processed for rockets-and liquid
oxygen (lox).  This is not the most powerful combination known, by a
wide margin, but it is much the cheapest-three cents per pound-so it is
economic good sense to use it for the first and largest stage of a
launch vehicle.

The second (S-II) stage burns high-energy liquid hydrogen and lox and
has a total propellant capacity of 460 tons, but because liquid
hydrogen is a dozen times as bulky as kerosene, it is not very much
smaller than the SIC stage.  Like that stage, it has five engines,
though much smaller ones, giving a total thrust of 500 tons.  Thus it
would be unable to lift itself off the ground under its own' power, and
can function only under orbital conditions.

The third (S-IVB) stage is also liquid hydrogen-lox fueled; it carries
115 tons of propellants and is powered by a single 100-ton-thrust
engine.  It is topped by a section

6 Anyone who drives into New York from Kennedy or La Guardia airports
can judge the size of this power plant for himself.  There is a
full-scale mockup, easily visible from the road, in the "Space Park"
just opposite the 1964-65 World's Fair site.

Plate 36.  The Saturn S-11 stage: sectional view.

North American Aviation, Inc.

Plate 37.  The Saturn S-IVB stage: sectional view.

North American Aviation, Inc.

Plate 38.  Apollo Command Module subsystems: sectional view.  North
American

Aviation, Inc.

Plate 39.  Apollo "Service Module subsystems: sectional view.  North

American Aviation, Inc.

carrying the electronics for guiding and controlling the whole launch
vehicle; and on top of that is the final payload-the Apollo spacecraft
itself, which is the only thing left when the spent components of the
gigantic Saturn 5 have dropped back into the sea or joined the rest of
the debris now orbiting Earth.

At this point it may be as well to take an inventory and to list the
vital statistics of the complete vehicle and payload.  It must be
realized that

Table 5 could easily be expanded into a whole shelf of thick vnlumes,
since it summarizes the activities of more than 20,000 companies
(including many of the largest in the world) and hundreds of thousands
of individuals.

Table 5 gives the cold facts of the Saturn 5 vehicle; no one would have
believed most of them a few years ago.  For when those five F-I engines
ignite, the mass of a fully loaded destroyer will climb straight up
into the sky.

Plate 40.  Apollo mission; model of Lunar Module.

NASA

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THE MISSION

An Apollo mission begins many months before the dramatic moment when
the first stage is ignited, and a hundred million horsepower of manmade
thunder rolls along the Florida coast.  It begins in a thousand
factories, where giant fuel tanks are fabricated, rare metals are
machined into strange shapes, and electronics systems are assembled
into sealed boxes worth many times their weight in gold.

It continues while all these myriads of components some weighing many
tons, some barely visible to the eye-converge on Cape Kennedy.  Whole
books could be written about this fantastic place, making no more than
a brief mention of the missiles and vehicles it exists to serve.

The ground support equipment, communications and radar, control
centers, fuel-storage tanks, gantries-and not least the enormous
quantities of real-estate involved represent an investment that must
now total several billion dollars.  And " investment" is the correct
word; unlike the present generation of one-shot launch vehicles, the
facilities at the Cape can be used over and over again.  They will be
ready and waiting when the, time comes to go to

Mars.

The monuments of the new age of exploration stand for miles along the
cape the Spaniards called Canaveral when they left their bones and
their treasure here four centuries ago.  The largest of all these
structures is the Vehicle Assembly Building, designed to bold, service,
and check out four Saturn 5's simultaneously.  It is more than 500 feet
high; through its door the entire United Nations 197

Building could be pushed, with room to spare.

Yet when you see it first, the V.A.B. does not look particularly
impressive.  Because it is a plain, cubical box, there is no sense of
scale; it is just another building on the flat Florida skyline.  It is
a little while before you realize that it is still 5 miles away.

And when you are standing in front of it, it still doesn't seem
unusually large.  For, by that time, your mind has simply rejected it
in self-defense.

After it has been assembled inside the V.A.B."  a Saturn 5 is enclosed
by movable floors and working platforms, so that all one can see of it
at any level is what looks like a section of a 33-foot-diameter storage
tank, coming up through the floor and going on through the ceiling.
Here it stays for several weeks while all its systems are checked out,
largely by automatic equipment conducting computer-controlled test
programs.

When everything is ready, the doors of the V.A.B. slide upward and
the

Saturn 5 slowly emerges, riding on the largest vehicle ever built.  The
3,000-ton "Crawler" is really a land-going ship; each of its eight sets
of caterpillar tracks is higher than a man, and they support a platform
half the size of a football field.  On this stands not only the Saturn
5 but also the 400-foot-high umbilical tower, with the numerous access
platforms, propellant supply lines, electric-power and control
connectors, and so forth needed to fuel and service the rocket.  The
Crawler can carry a load of 6,000 tons, and its driver's cabin and
controls seem absurdly small-until one stops to think that the driver
is just the same size as usual.  A series of hydraulic jacks keeps the
load vertical as it rolls along the 3 miles of special highway to the
launching pad; flat out, the

Crawler can frit N' miles an hour.  I once noticed Representative
George

Miller, chairman of the House Committee on Astronautics, to ving
thoughtfully with the controls-and warned him not to try breaking the
local speed limits, because Chief justice Warren was standing right
behind him.

In the past, space vehicles have been erected and checked out on the
pad from which they were to be launched, but this is impracticable for
boosters of the Saturn 5 class.  The launch pads, which have to absorb
volcanic beats and.  earthquake impacts from the rocket blasts, are so
massive and so expensive that it is uneconomical to monopolize one for
weeks, or even months, while a single vehicle goes through its
elaborate test procedures.  Separating the launch and assembly
operations results in much greater efficiency; moreover, inside the

V.A.B. the great rockets can be fully protected from the weather,
including, it is hoped, the hurricanes that occasionally lash the
Florida coast.

When all systems Nvere in readiness for the first Apollo flight to the
Moon and the immense vehicle was fully loaded with its propellants, the
three astronauts crossed the catwalk-more than 300 feet from the
ground-into the

Command Module, which was to be their home for many days and half a
million miles.  All the time, automatic checking equipment was probing
and testing every vital component, while the last seconds before the
moment of departure ticked away.

The "launch window"-the interval during which the mission is
possible-opened; the five F-1 engines thundered into life.  Watched by
more people than any previous event in the history of the world, the
rocket started to climb toward the sky.

At first it moved very slowly; the full thrust of four of its giant
engines is required merely to balance its weight, so only the fifth can
provide acceleration.  It took almost ten seconds-and they seemed very
long seconds indeed for the rocket to lift through it own length and to
clear the umbilical tower.  But as it lost weight it gained speed more
and more rapidly, curving away from the vertical and beading out over
the sea along its pre programed trajectory.  Any deviations from the
desired course would be corrected by signals from the onboard
electronic brain in the instrument unit, housed immediately beneath the
Apollo spacecraft compartment.  Four of the SIC stage engines are
gimbaled-the central one is fixed-and their barely perceptible
movements would keep the vehicle on its course.

In two minutes the first stage had burned its 2,200 tons of
propellants; it was jettisoned and driven backward from the remainder
of the vehicle by retrorockets.  The second stage-the S-11-ignited.

At this point the solid-fueled emergency escape system, mounted on the
top of the Command Module, was also discarded.  It was no longer needed
to jerk the spacecraft to safety in the event of an abort near ground
level; the vehicle was now 30 miles up, and if anything went wrong the
CM could return by its own parachutes.

The booster was still climbing when the second stage exhausted its
liquid hydrogen and was dropped.  The third-S-IVB-stage ignited, and it
continued to thrust until it had driven the spacecraft into a circular
"parking" orbit, at an altitude of 115 miles.  Then it was cut off, but
with most of its propellant still unburned.

Now the whole spacecraft assembly was orbiting Earth, only 115 miles
up, at 17,500 mph.  It could remain there for weeks if necessary, while
the crew carried out further checks.  If for any reason it was decided
to abandon the mission at this stage, it would be easy enough to
deorbit and re-enter the atmosphere.

But the flight was going perfectly, and so the spacecraft used its
still attached, partly fueled S-IVB stage to break out of the parking
orbit, at the correct moment, to head for the Moon.  The S-IVB's
remaining propellant was just sufficient to give the extra 7,000 mph
needed to reach escape velocity; at burnout, the Apollo spacecraft and
the now empty stake were receding from Earth at 25,000 mph.  In 70
hours of free coasting, they would reach the Moon.

Now followed, at the beginning of the outward leg, some complicated
maneuvering-in fact, a kind of mini rendezvous  It will be remembered
that the Lunar Module" Not Needed On Voyage," as the baggage labels
have it-is stowed away below the Service Module.  But this means that
the SM's propulsion systems, required for entry into lunar orbit,
cannot be used; the LM is sitting right beneath the rocket exhaust.  So
it has to be moved around to the front.

To make this possible, the Apollo astronauts cut their spacecraft
neatly in two with explosive charges, so that it separated into the
Command and

Service modules on one side, the LM and the empty S-IV stage on the
other.  (A look at Plate 43 is recommended at this point; this whole
operation is easier depicted than described.) Under very gentle bursts
of power from its control jets, the Command Service-module assembly-now
a small, self-contained spaceship-was turned around through 180 degrees
and (locked with the LM, so that the CM and LM met head-to-head.  The
maneuver is exactly like a shunting operation in a railroad marshaling
yard, when a coach is switched from behind to in front of an engine and
its tender.

It should be realized that if for any reason this turnaround and
docking maneuver had failed, the result would not have been a disaster,
though it would have certainly been an expensive disappointment.  The
Command and

Service modules could have continued to the Moon and circumnavigated
it; but of course the LM would have had to be abandoned in space, and
no landing would have been possible.

The empty S-IVB third stage and its attached instrument unit, were now
jettisoned.  All that was left, coasting toward the Moon, was the
odd-looking head-to-head LM and CM combination, plus the Service
Module, attached to the base of the CM.

These operations had all taken place quite close to the

Earth, right at the beginning of the translunar trajectory.

Perhaps this is of psychological rather than practical importance, but
at least if anything had gone wrong all this maneuvering would have
been clearly visible, weather permitting, in ground-based telescopes.
An d, of course, at this range radio and TV communication would be
excel lent.

The voyage now had begun; nothing (except a collision with a really
large meteoroid) could stop the spacecraft from reaching the
neighborhood of the

Moon in approximately three days.  Astronomical and radio observations
would be made continually to check the orbit; if needed, there would be
a midcourse correction.

At last the spacecraft started to accelerate, increasing its speed as
it fell into the Moon's gravitational field.  Only a few hundred miles
from the surface, at a carefully calculated moment, the Service
Module's engine started to fire for the first time in the voyage,
slowing the spacecraft to about 3,500 mph.  This put it in a circular,
two-hour orbit about 70 miles above the surface of the Moon.

To orbit the Moon was the triumphant achievement of the Apollo 8
astronauts-Colonel Frank Borman, Captain James A. Lovell, Jr."  and
Major

William A. Anders-in their historic flight of December, 1968.  These
lunar circumnavigators left Cape Kennedy atop their Saturn 5 rocket on
December 21, entering an orbit around the Moon 69 hours later, and
relaying to Earth breathtaking television pictures -of the Moon's
desolate, crater-scarred face from a distance of 70 miles.  After
orbiting the Moon 10 times in 20 hours they returned safely to Earth,
having begun a new chapter in the story of human exploratiom But their
voyage around the Moon was only a preliminary to the lunar landings
ahead.

Another necessary preliminary came in March, 1969, when the Apollo 9
trio-James A. McDivitt, David R. Scott, and Russell L.
Schweickart-successfully tested the LM docking techniques in an Earth
orbit.  Two months later, the men of Apollo 10-Thomas R. Stafford,
Eugene A. Cernan, and John W. Young-repeated the Apollo 8 lunar orbital
flight, but this time took the LM on a practice descent to within 9
miles of the Moon's surface.  Now, at last, all was ready for the
full-scale Apollo mission that began on July 16, 1969, and culminated
in the lunar landing of Neil A. Armstrong and Edwin E. Aldrin, Jr."
with Michael Collins orbiting in the

Command Module above them.

The landing maneuver required the spacecraft to make several
revolutions in its parking orbit while the crew prepared for the
descent.  Then Armstrong and Aldrin transferred to the LM; well may
they have wondered, in that tense moment, "When shall we three meet
again?"

After a pre-descent checkout, the LM separated from the Command
Module.

Using the larger of its two engines as a retrorocket, it reduced speed
and dropped toward the Moon, while Collins and the Command Module
remained overhead in orbit.  The two vehicles were in sight of each
other, as well as in direct radio contact, during this phase, so
Collins was able to monitor the whole landing operation.

As it approached the chosen landing place in the Sea of Tranquility,

Armstrong had to take manual command of the LM, steering it past some
troublesome-looking boulders and bringing it safely to rest in a level,
rock-strewn plain.  "Tranquility Base here," Armstrong radioed at
4:17:40

P.m. Eastern Standard Time on Sunday, July 20, 1969.  "The Eagle has
landed."

The Eagle-code name for Apollo 1 I's LM-remained on the Moon for less
than 24 hours.  First Armstrong and then Aldrin went outside, wearing
protective spacesuits, to collect rock and soil samples, make
observations, and install scientific equipment which was left on the
Moon to radio information back to Earth.  In man's first eye-witness
de

Plate 43.  Apollo mission: Command and Service Modules separate from
LMIS-IVB stage.

North American Aviation, Inc.

Plate 45.  Apollo mission: Command and Service Modules dock with
Lunar

Module.  North American Aviation, Inc.

Plate 44.  Apollo mission: Command and Service Modules turn around to
prepare for docking.  North American Aviation, Inc.

Plate 46.  Apollo mission: jettisoning of.~-IVB stage after docking.
North

American Aviation, Inc.

Plate 47.  Apollo mission: Command and Service Lunar Modules braking
into lunar parking orbit.  North American Aviation, Inc.

Plate 48.  Apollo mission; Lunar Module separates from Command and
Service

Rodules.  North American Aviation, Inc.

Plate 49.  Astronaut Edwin E. Aldrin, Jr.  descends to the sur lace of
the

Moon on the Apollo 11 mission.  NASA

Plate 50.  Astronaut Aldrin on the Moon.  Astronaut Neil A. Armstrong,
who took the picture, is reflected in Aldrin's faceplate, as is the
Lunar

Module.  NASA

Plate 50a.  Apollo ]Fs Lunar Module on the Moon.  Astronaut Aldrin can
be seen in foreground.

NASA

script ion of another heavenly body, Armstrong reported, "The surface
is fine and powdery.  I can pick it up loosely with my toe.... I can
see the footprints of my boots in the treads in the fine sandy
particles." The entire Moon walk, beginning with the moment of
Armstrong's "one small step," was watched by much of the human race
over television. This was not merely a publicity gimmick

(though the American taxpayers certainly deserve their money's worth),
but a sensible precaution.  Pictures can convey more than thousands of
words, especially if some emergency should arise.  In that event, the
TV camera might be the only reporter.

The day after they had written their astonishing new page in human
history, the men in the LM took off from the Moon, using their module's
landing gear as a launch pad and leaving the empty fuel tanks, the
descent engine, the shock-absorbing legs, and an assortment of other
equipment as souvenirs for future explorers.  Under the power of the
small ascent engine, they climbed back to orbit and made a rendezvous
with the Command Module.  The vehicles docked together, and the two men
aboard the LM-or what was now left of it, the Lunar Launch
Stage-rejoined their companion.  The LM then was jettisoned, remaining
in lunar orbit.

Once more there was an orbital checkout, the final one, to prepare for
the return journey.  At the right moment, the Service Module's engine
was fired; almost all its remaining fuel was used to achieve escape
from the Moon.

Only an extra 1,500 mph was needed to do this; then the two modules
were on their way back to Earth.

The homeward journey took about 2,12' days.  Precise calculation of the
course was essential, for the returning spacecraft, building up to a
speed of 25,000 mph as it fell back through the Earth's gravitational
field, had to enter a corridor only 60 miles deep in order for the
atmospheric braking to be carried out properly.  If it came too low, it
would burn up; too high, and it would shoot on out into space once
more.

A few hours before re-entry, the faithful Service Module was
jettisoned; now, of the 360 feet of towering rocket that started from
Cape Kennedy, only the squat 11-foot cone of the Command Module was
left.  Using small attitude-control jets, the CM flipped itself around
so that its base-the heat shield-was pointing in the direction of
motion.  The atmosphere thickened around it; resistance built up
rapidly, and the energy acquired in a fall all the way from the Moon
was dissipated in a meteoric trail arcing high across the Pacific.

The Command Module was not quite unguided even during the last minutes
of its blazing descent.  The pilot could fly it, to some extent, by
altering its angle of tilt and could thus vary his landing point by
several thousand miles.

Twenty-five thousand feet above the ocean, the Command Module, its heat
shield still glowing redly, had spent its energy.  Three giant
parachutes deployed and lowered it to the sea, where the recovery ships
were waiting.

And then the returning lunar voyagers were hustled off into a
three-week period of quarantine, lest it turn out-and it did not-that
they had carried some infectious microorganism back with them from the
Moon.

Jules Verne described the scene, exactly a century earlier, when his
three astronauts returned from their voyage from Florida to the Moon
and back, and were found bobbing on the waves by the United States
Navy's corvette

Susquehanna.  The imperturbable Barbicane, Michel Ardan, and Nieboll
were playing dominoes when the boats reached them.  Perhaps NASA should
have included a set in the Apollo Command Module, as a tribute to the
great master, who inspired, without exception, all the pioneers of
astronautics.

TABLE 6

TYPICAL APOLLO MISSION

1. First-stage (SIC) ignition and launch 2. SIC cut-off and jettison
3.

Second-stage (S-11) ignition 4. jettison Launch Escape System (LES)
5.

S-11 cut-off and jettison 6. Third stage (S-IVB) ignition 7. Insertion
into 115-mile circular Earth parking orbit 8. S-IVB cut-off 9.

Parking-orbit coast; checkout crew and equipment 10.  S-IVB re ignition
11.  Escape velocity attained; injection into Earth-Moon transit
trajectory 12.  S-IVB cut-off 13.  Explosive separation of spacecraft
LM adapter 14.

Command/ Service Modules separate from LM/S-IVB stage 15. Command/
Service

Modules turn around and dock with LM 16.  S-IVB stage jettison 17.
70-hour coast to Moon; mid-course corrections 18.  Service Module
ignition

TYPICAL APOLLO MISSION (continued)

19.  Braking into lunar parking orbit 20.  SM cut-off 21.  Lunar
parking-orbit coast; crew and LM checkout 22.  Two men transfer to LM
23.  LM separates from Command/ Service Modules 24.  LM landing-stage
ignition 25.  LM enters transfer orbit to lunar surface 26. Command/
Service Module (one man) remains in parking orbit 27.  LM engine
cut-off 28.  LM coasts down to near lunar surface 29.  LM hovers,
selects landing site, touches down 30.  Lunar stay-observation,
experiments, sample-gathering 31.  LM launch-stage ignition; landing
stage left on Moon 32.  LM launch-stage cut-off; coast up to parking
orbit 33.  LM mid-course correction 34.  LM launeb-stage ignition;
entry into parking orbit 35.  LM launch-stage cut-off 36.  Rendezvous
and docking with Command/ Service Modules 37.  Transfer of crew and
scientific material from LM to Command Modules 38.  LM launch-stage
jettison 39.  Command/ Service Module checkout prior to lunar-orbit
escape 40.  Service Module ignition 41.  Injection into Moon-Earth
trajectory 42.  Service Module cut-off 43.  2% days of coasting;
mid-course correction 44.  Modules separate; Service Module jettison
45.  Command Module assumes re-entry attitude 46.  Command Module
enters atmosphere 47, Command Module loses speed, controls flight
toward landing point 48.  Heat-shield jettison 49.  Parachutes released
50.  Water landing

Moon at 4119Moon at takeoff landing 21 Orbit of Moon

C.3)

Fig.  16.  The Apollo mission.

THE MOON

Until a few years ago-say, up to 1964-astronomers thought they knew a
great deal about the Moon.  They had been studying it, with telescopes
of ever-increasing power, for three and a half centuries, and many had
spent their entire lives making beautiful maps of the details visible
on its surface.  Those maps-and the splendid photographs taken by such
instruments as the 100and 200-inch reflectors-gave an illusion of
knowledge which was abruptly shattered by the Ranger, Luna, Surveyor.
and Orbiter spacecraft of the mid-1960's.

Looking at an Earth-based photograph like that in Plate 51, it is easy
to forget that the smallest object that can be seen is about half a
mile across and that what is presented here is no better than a
naked-eye view from 1,000 miles away.  What would we really know of our
own planet-its surface texture, its small-scale topography, everything
that goes to make up the environment which controls our lives-if we
could perceive no details smaller than a super tanker or the Pentagon
building?

Telescopic photos were also misleading for another reason; they were
almost always made under slanting sunlight, so that shadows stood out
dramatically and all slopes, valleys, or hills were greatly
exaggerated.  Though all serious students of the Moon were perfectly
well aware of this, it was difficult even for them to avoid the mental
picture of a rugged world of sharp peaks and steep-sided canyons; and
popular artists, who naturally wanted their illustrations to be as
exciting as possible, made little effort to put the record straight.

Of course, there was a large body of facts which were not in dispute
and which have remained unaffected by the discoveries of the Space Age.
The

Moon's diameter-2,160 miles-is one quarter of Earth's, so its surface
area is one-sixteenth.  This may seem rather small, but since three
quarters of our planet is under water and has until recently played no
part in Man's explorations, it would be less misleading to say that the
Moon has one-fifth of the land area of Earth.  This is 14 million
square miles of new territory, slightly larger than Africa.

The Moon has no atmosphere and no water-at least in the free state.
Whether it possessed either in the past is uncertain; its gravity-only
one-sixth of

Earth's-is too feeble for it to have retained any gaseous envelope over
astronomical periods of time.  Any primitive atmosphere must have
leaked away into space, ages ago.

The absence of an atmosphere has profound effects upon the lunar
environment.  Some are obvious; others are more subtle; and there will
be many (perhaps the most important) which we will not discover until
we get there.

Among the obvious ones are the total silence; there can be no sound on
the

Moon, though there can be ground transmitted vibrations.  (Signaling
systems may be de

Plate 51.  Moon as seen.  Iront Earth.

Mount Wilson and Palomar Observatories ve loped using these.) There can
be no large, active life forms of the type that exist on Earth, for
these are all burners of gaseous oxygen.  The sky will be black, and
because there is no scattered light, the stars will be visible even in
the daytime, but only if the viewer shields his eyes completely from
the surrounding glare and waits until he is dark-adapted.

Above all, there will be tremendous temperature changes between day and
night, and even between sunlight and shadow.  in a few hours, or over a
distance of a few feet, the temperature can range between plus and
minus 200 degrees Fahrenheit.

The subtler effects of the vacuum environment will concern the nature
of the lunar surface-its physical structure and its behavior when
disturbed.

Volcanic rocks (if they exist) may be very light and porous, prehaps a
kind of froth or foam.  There will undoubtedly be minerals and types of
rock which do not occur on Earth.  And there will be none of that sense
of distance which gives scale and perspective to terrestrial landscapes
by reducing the contrast and definition of remote objects.  A boulder
10 feet away well appear as sharp as a mountain 10 miles away; that is
why such panoramas as that in Plate 33 have a slightly unreal,
model-like appearance.  There is no atmospheric haze to tell the eye
that it is looking across 50 miles of moonscape and that the mountains
in the foreground are thousands of feet high.

When the full Moon rides in the night sky, it looks a dazzling object,
and the adjective "silvery" seems appropriate enough, but this is
another illusion.  It appears brilliant only by contrast against the
utter blackness of space, and it is in fact a very poor reflector
indeed.  At close quarters, it has about the optical qualities of dirt.
Careful studies of the way in which sunlight is scattered back to Earth
during the course of the lunar day had convinced most astronomers, even
prior to the Luna 9 and

Surveyor I landings, that the Moon's surface must be extremely porous,
full of minute holes that trapped most of the sunlight falling upon it.
Green cheese definitely would not fit the specifications, but stale
black bread might.

Even a casual glance at the Moon with the naked eye shows that its
brightness varies over its surface, producing patterns which have been
the raw material of myths and legends since time immemorial.  The
telescope confirmed these, and when it was found that the bright areas
were mountainous, whereas the dark ones were much flatter and at a
lower level, they were given the names of seas (in Latin, mare, plural,
maria) or oceans.

Although it soon became obvious that there was not even a single small
lake on the Moon, the Sea of Crises, Ocean of Storms, Bay of Rainbows,
etc., remain as charming reminders of the first age of lunar
exploration.

The lighter areas of the Moon are peppered with hundreds of thousands
of circular rings, or craters, ranging in size from 150 miles in
diameter down to a fraction of a mile across.  (As we now know from the
Ranger photographs, they continue on down to diameters that must be
measured in inches.) The origin of these craters has been the subject
of a bitter controversy for more than a hundred years; apart from those
entertaining crackpots who thought that they were coral atolls,
phenomena in a lunar atmosphere, or the results of thermonuclear
brinksmanship, the serious students of the Moon divided themselves into
two classes-those who believed that the craters were due to the impact
of enormous meteoroids, and those who considered that they were
volcanic, or at least produced by internal, igneous forces.

It now appears that the controversy will be settled in the usual way;
both sides are probably right.  It seems indisputable that the most
extensive of the lunar formations, including many of the great
seas-which are almost perfectly circular-are due to impact phenomena on
a gigantic scale.  This would probably have been accepted long ago if
the extraordinary formation known as the Mare Orientale (Plate 52) had
been on the visible face of the

Moon.  But, as luck would have it, this 600-mile-diameter example of
cosmic target practice lies almost entirely in the lunar Farside, so
that only its outermost ring of mountains can be seen from Earth.
Orbiter 4 (1967) was the first to reveal its true structure.

Yet there are many other features on the Moon that cannot possibly be
due to such sudden, catastrophic events.  There are clear traces of
lava flow, channels that!  look almost like dried-up riverbeds, and
suspicious stains that may be deposits from volcanic outgassing.  The
dark 11 seas" themselves appear to be composed of some material which
has flowed over, and perhaps melted down, many ancient craters; some
have been only partly obliterated, while others appear merely as buried
ghosts, like the foundations of lost cities in aerial photographs.

Perhaps the remarkable formation known as Tsiolkovsky is the most
striking example of this (Plate 3).  This giant crater-or small sea-was
first detected by Luna 3; it is the most conspicuous formation on the
far side of the Moon, and few would grudge the Russian astronomers the
name they gave to it.  But it took the United States' Orbiter 3 to show
that it is full of some intensely black material that seems to have
congealed in the very act of melting down the surrounding, brighter
walls of the mountains that contain it.

A great deal has been happening on the Moon; it is a much more
complicated and interesting place than we imagined a few years ago.
There is also increasing evidence that it is by no means dead,
geologically (or selenologically) speaking.  Physical changes,
obscuration of features by temporary clouds or gas emissions, and even
minor volcanic activity have been reported by amateur

Plate 52.  The Mare Orientale on the far side of the Moon, photographed
by

Lunar Orbiter 4 on May 25, 1967.

NASA

astronomers for years.  No one took them seriously, partly because,
until quite recently, the professional astronomers had no interest in
the Moon at all.  Now the situation has radically changed, and there
are teams on the alert, with special instruments, for any sign of lunar
activity.  Apart from its scientific interest, this may reveal sources
of power or valuable minerals for future explorers.

It is also possible, though unlikely, that it may indicate the
existence of microclimates-locally favorable regions where life may
exist.  The first telescopic observers were quite sure that the Moon
must be inhabited-it was almost blasphemy to suggest that the Creator
would waste a world-but as understanding of lunar conditions grew, this
belief was reluctantly abandoned.  It seemed quite impossible that any
form of life could survive on a world with no atmosphere and no free
water, although it was not out of the question that the Moon might have
had a brief evolutionary episode in its youth.  In that case, there was
the faint chance that fossils might be discovered, but nothing more.

The pendulum has now swung again, not back to the nal ve optimism of
the seventeenth century, but at least to a less pessimistic viewpoint
than that of the early twentieth.  We now know very much more about the
adaptability of life, especially at the microscopic level, and have
discovered that there are plenty of organisms that can thrive in a
vacuum, and even some that are killed by air.  If life ever got started
on the Moon-perhaps in some long vanished lunar sea-it may still be
there.  Any biologist worth his salt could design a whole menagerie of
plausible Selenites, granted the existence of a few common chemicals on
or below the lunar surface.

Anyone who finds this hard to believe should look at the deserts of
the

American Southwest.  From the air they appear to be utterly barren and
empty; but as Walt Disney showed in one of his nature films, the desert
is really seething with life.  So let us reserve judgment on the Moon,
at least until we have explored a great many of its 14 million square
miles, and not merely the areas around a few landing sites.

This exploration is a task which will occupy us for decades, if not for
centuries.  Although the Moon will be mapped and photographed and
probed by innumerable low-level satellites, the fine details must be
filled in by the geologists with hammers and microscopes and Geiger
counters and neutron activation analyzers.  It may turn out that large
areas of the Moon are so similar that there is no point in making more
than a few limited surveys; but it may also turn out that it has almost
as much variety as Earth, though of very different kinds.

Nature is always far richer and more complex than we can imagine.  When
the first scientific satellites were being planned, there were those
who could see little point in them, because, after all, there was
"nothing" in space.

Now we have discovered that it is teeming with strange radiations,
swept with tenuous gales of solar gas, drenched with signals-and
perhaps messages-from distant galaxies, permeated by magnetic fields
which may control the destiny of the stars.  What had appeared empty
has turned out to be inexhaustible.

So it may be with the Moon.  A generation ago, it seemed a dusty slag
heap in the sky.  Now, thanks to the impact of the voyages of the
Apollo astronauts, it has suddenly become a real and tangible country,
full of wonder and mystery and the only wealth that time can never
destroy-knowledge.

THE USES OF THE MOON

What the human race will do with the Moon during the centuries to come
may be as far beyond imagination as the future of the American
continent would have been to Columbus.  Nevertheless, it is possible to
foresee certain lines of development, culminating, not only in large
permanent lunar bases but also, ultimately, in self-sufficient colonies
and even projects to make the whole Moon habitable.  Such a suggestion
should no longer seem fantastic; if we have learned one thing from the
history of invention and discovery, it is that in the long run-and
often in the short one-the most daring prophecies turn out to be
laughably conservative.

The first lunar explorers will be concerned chiefly with survival and
with collecting as much scientific information as possible from a
restricted area and in a limited time.  They will have very little
mobility; a spacesuit can provide oxygen and life support for only a
few hours, and is not the most comfortable garb for long-distance
biking, even where everything has only one-sixth of its terrestrial
weight.  ,

Walking, in fact, may be quite difficult on the Moon; weight is barely
sufficient to provide traction.  Explorers may have to develop a new
mode of locomotion, perhaps a sort of buoyant stride.  They would be
well advised to avoid the spectacular leaps popular in space fiction;
loss of balance and a head-first landing could easily be fatal.

Spacesuit design involves complexities that can only be hinted at here;
in some ways it is easier to design a 222 * THE PRONaSE OF SPACE
spaceship than a spacesuit.  They must both contain the same
life-support system, but the suit must also be flexible and
form-fitting.  The men who wore the first models felt as if they were
living inside inflated tires; the pressure made the suits so rigid that
it was almost impossible to move.  One way of avoiding this problem may
be the constant-volume suit, a semirigid structure very much like
medieval armor.

Temperature control is of prime importance, especially on the Moon
during the daytime, when the exposed rocks will be hotter than boiling
water and the Sun will be dumping almost two horsepower of pure heat on
every square yard.  However, this problem should not be exaggerated;
thanks to the lunar vacuum, it is easier to handle heat loads on the
Moon than in the dry, tropical deserts of Earth.  The almost
ludicrously simple expedient of an adjustable sunshade will suffice; we
may have to get used to the spectacle of lunar explorers carrying
Robinson Crusoesque umbrellas.

It will be extremely frustrating to come all the way to the Moon, and
then be limited to ranges of a couple of miles around the spacecraft.
(From the

LM window the horizon is about 2136' miles away, and though radio
contact could be established over a greater distance, it would be
wisest for the astronauts always to keep in sight of each other.) As
soon as possible, therefore, some kind of lunar transport vehicle must
be provided, preferably one which will allow the explorers to work in a
shirt-sleeve environment, so that it will serve as a mobile base and
laboratory.

On a one-way trip, the Saturn 5 could land several tons of supplies on
the

Moon, and there have been many NASA and industry studies of ways in
which this capability could be used to support lunar operations.  For
example, the

Apollo Logistic Support System (ALSS) envisages the use of a modified
Lunar

Module-a "LEM Trucle'-to put 7,000 pounds of cargo on the Moon.  Most
of this might consist of a surface vehicle, weighing two or three tons,
which could carry two astronauts on a 14-day exploration mission
covering several hundred miles.  It would be able to unload itself
automatically from the descent stage which landed it on the Moon, and
would await the arrival of its passengers in a later LM.

Numerous odd vehicles have been designed-and some built-to test these
concepts.  Uncertainty about the nature of the lunar surface, and
particularly its bearing strength, resulted in moon rovers which
traveled on wheels, caterpillar tracks, legs-and even some that hopped
or drilled their way through the thick layer of dust which some
theorists had confidently predicted.

It is quite possible that every sensible theory of the lunar surface is
true, somewhere, and that all these vehicles may eventually be needed.
But when Surveyor I photographed its own footprint (Plate 53), a
collective sigh of relief went up from the engineers who had to design
transportation and landing systems.  It almost seems as if the Moon's
surface-or much of it-is the ideal compromise.  Unlike rock, it yields,
and so absorbs the shock of impact; but it also has considerable
bearing strength, and most types of vehicle could make good progress
over it.  So could a walking man, once he was accustomed to the
gravity.

A lunar supply operation based on the Apollo-Saturn 5 system or modest
extensions of it could maintain a scientific base on the Moon at a cost
of about fifty million dollars per man-year.  (Some people in the
business have been quick to point out that one can afford to pay a
pretty good salary to a man whose upkeep costs fifty million a year.)
Long-term programs of lunar exploration, therefore, will have to be
justified on the grounds of scientific value or practical applications;
national prestige, after the first landings, will not be enough.

On the purely scientific side, we can still make no more than educated
guesses; it has been truly remarked that, if we knew what we'd find on
the

Moon, there would be no need to go there.  But the geologists and the
astronomers are already convinced that the Moon is a treasure house of
knowledge that can be found nowhere else; as one has put it, "a
virtual

Rosetta Stone that, if properly read, may permit us to learn how the
solar system, the earth, and the continents on which we live were
formed."

Until now we have had only one planet for study; we do not know in
which ways our Earth is typical (if this word means anything), and in
which it is unique.  Almost all its surface features have been shaped
and reshaped by wind and rain, until practically nothing has been left
of its primordial crust.  The "eternal" mountains are jerry-built
structures which were thrown up yesterday and will be

Plate 53.  Surveyor I photograph of the Moon's surface and its own toot
pad computer-enhanced to show granular surface particles as small as
1150 of an inch.

NASA

torn down tomorrow.  On the very rim of the Grand Canyon-already
hundreds of millions of years back in time-may be found the sponges and
corals of recent seas; in the miles of rock below lie the records of
far more ancient oceans interleaved with the ruins of continents that
have come and gone and come again in the four billion years since the
crust of our planet congealed.

There are still greater canyons on the Moon (Plate 56); what story do
they tell?  A very different one, it is certain.  Despite the evidence
of massive bombardment in the remote past, the Moon may furnish a much
more complete and undisturbed geological record than the Earth can ever
provide.  Not only the scientific, but also the practical-and

even commercial-importance of this can hardly be overestimated.  We do
not know, for example, why metallic ores are distributed and
concentrated as they are in the Earth's crust. The Moon may help us to
answer this question, with economic consequences that could- pay for
any lunar exploration program a hundred times over.

Even from Earth-based photographs it has been possible to identify
twenty different types of lunar features, indicating a complex
geological history.

They include craters of at least five different ages, rills, domes,
rays, crater chains, central peaks, wrinkles, maria, highlands.  Now,
closeup photos have produced many more; for example, there are curious,
shallow depressions that appear to indicate some type of subsidence, as
if surface material has drained away into underground cavities.  And
there is, surprisingly, much evidence of erosion; even to a casual
glance, some craters look worn and smoothed down, whereas others are
still sharp and new, meaning, perhaps, no more than a few million years
old.

Drilling rigs, seismometers to detect artificial moon quakes-or natural
ones, if they exist-gravimetric, electrical, gamma-ray, and magnetic
surveying instruments, will be just a few of the devices used to probe
the

Moon's interior.  When one considers how long it has taken to unravel
the past history of our own world, and how much still remains to be
done, it is obvious that the Moon will keep us very busy for centuries
to come.

Every question that is answered will pose a dozen more, and we must not
assume that even the apparently straightforward questions will be
easily settled.  A classic example of this is given by the odd case of
the American geologist G. K. Gilbert, who first put the meteoric theory
of lunar craters on a sound scientific footing.  Gilbert also devoted
much time to the famous

Barringer Crater in Arizona and eventually decided that it was not
meteoric, but volcanic.  Today we are quite certain that it was indeed
caused by the impact of a large body from space, and it is regarded as
one of the best proofs of Gilbert's theory-thougb his own verdict
prevented this fact from being recognized for about thirty years.  This
instructive episode once led me to predict that as soon as we land the
first two geologists on the Moon, in ten minutes they will be throwing
rocks at each other in defense of their rival theories.

Plate 54.  (felt) The Hyginus Rille, a lunar canyon photographed by
Lunar

Orbiter 3 on February 18, 1967, at an attitude of 39 miles.

The Boeing Company

Plate 55.  (below) A 17-meter rolling rock and its 225meter-long
trail,

Vitelto Crater, photographed by Lunar Orbiter 5 on August 17, 1967. The
rock seems to have rolled uphill over part ol its path, as though it
gained momentum from a long downhill roll on the opposite high slope.

Boeing/ NASA

The Moon will also be of the utmost importance, not only as an object
of study but also as a base for an enormous variety of experiments.
Everything that has been said about the value of space stations for
physical, biological, and astronomical research also applies to the ,
Moon.  It also gives us an observation platform beyond the obscuring
effects of the atmosphere, but one of virtually infinite mass, upon
which instruments of any size could be mounted.  We will not be able to
take full advantage of this until we can obtain at least basic
construction materials from lunar resources, so that they do not have
to be carried from Earth; but even now there are a great many
experiments which may be performed more conveniently on the Moon than
in space.

One example lies in the exciting and brand-new field of X-ray
astronomy.  Since these rays cannot penetrate the atmosphere, the first
celestial X-ray sources were not discovered until rockets carried
instruments into space; and it is very difficult by this means to
pinpoint the fainter objects (some of which have been identified with
the baffling "quasars").  Dr.  Herbert Friedman of the United States

Naval Research Laboratory, a pioneer in this work, considers that the

Moon is an ideal site for a big X-ray telescope.  It could be based on
the 4oor of a crater and sighted at the surrounding rim; then, as an

X-ray "star" rose above the mountain wall, the moment it appeared could
be noted with great accuracy, and hence the location of this invisible
object could be found.  In such an experiment, the knife edge formed by
the solid body of the slowly rotating Moon would act as part of the
telescope system.

The Moon turns on its axis, with respect to the stars, once in every
27.3 days, and this very low rate of rotation makes it ideal as a base
for an astronomical observatory.  A celestial body can remain in
continuous view for two weeks at a time, and, of course, visibility is
always perfect.  Even the presence of the Sun would be little handicap,
as long as the telescope was shielded from its direct rays.

Two other crippling limitations of Earth-based instruments would also
be removed or greatly alleviated.  One is gravity; a large telescope
mirror weighs many tons, and its surface has to be shaped to an
accuracy measured in millionths of an inch.  But because no material is
rigid, it changes its shape and therefore loses its focus as it is

IL,

Plate 56.  This lunar canyon, 150 miles long and 5 miles wide at some
places, is located on the far side ol the Moon and was discovered by
Lunar

Orbiter 4. The Boeing Company moved in the Earth's gravitational field.
Extraordinary measures have to be taken to avoid this deformation.

On the Moon this problem would be vastly reduced.  Moreover, the whole
telescope structure, which has to be just as rigid as the mirror, could
be very much lighter.  Because it has to contend with our gravity, the
200-inch reflector on Mount Palomar weighs 500 tons.  A lunar
200-incher might have a mass of only 60 tons, and hence a lunar weight
of only 10 tons.

The second terrestrial limitation, or problem, is simply bad weather,
and there is no weather on the Moon, though perhaps some protection
from micrometeorites may prove necessary.  So no expensive domes will
be needed; the spidery telescope structure could be erected in the
open.

The radio telescopes even more than the optical telescopes will benefit
from this state of affairs.  The giant parabolic dishes which are now
one of the characteristic symbols of the Space Age have to be designed
to withstand the maximum wind forces they are ever likely to
encounter-as well as gravity.  They also have to keep their shape and
alignment with great precision; it is not surprising, therefore, that
they are among the most massive and expensive structures yet built by
man.  On the windless, low-gravity Moon, the design problems would be
simplified to an unbelievable extent.

And as if that were not enough, the Moon has yet another-possibly
overwhelming-advantage for the radio astronomer.  Already, here on
Earth, he is harassed by electrical interference from myriad motors
automobiles, ielevision stations and thunderstorms; a ingle electric
shaver can put a $10 million radio telescope out of business during a
crucial observation.  (All radio astronomers have horror stories of
such incidents.) But the very center of the far side of the Moon is the
only place in the whole Solar

System that is permanently shielded from our noisy planet-by 2,000
miles of solid rock.

This, of course, is a consequence of the fact that the Moon keeps the
same face always turned toward us; it revolves on its own axis in
precisely the same time that it takes to go around the Earth.  Needless
to say, this "synchronous" rotation is nota coincidence; the braking
action of the Earth's gravitational field has robbed the Moon of its
initial spin and slowed it down until it has entered its present stable
state.  (The Moon is returning the compliment; in some billions of
years it will have slowed the Earth down, so that one hemisphere always
faces it; and then moonrise and moonset will be no more.)

For centuries astronomers have been tantalized by the fact that almost
half of the Moon is permanently hidden from them.  Now the time is
coming when they may be thankful that the Earth is permanently hidden
from half the

Moon.

In the 1930's a science-fiction magazine published a story called
"The

World Behind the Moon," based on the idea that there might be a second
moon of Earth, forever bidden from us by the one we know.  It is just
the sort of idea that would appeal to mystics; the old concept of a 11
counter earth on the other side of the Sun is a similar one.

A little knowledge of astronomy (see the discussion of orbits in
Chapter 6) appears to show that this idea is nonsense.  A body behind
the Moon, and therefore more distant from the Earth, would move more
slowly in its orbit.

Thus it would quickly lag behind and become visible from Earth.

However, this is a case where a little knowledge is, if not dangerous,
at least misleading.  When the effect of the Moon's own gravity field
is added to the Earth's, it can be shown that there is a point, L2,
35,000 miles behind the Moon, where a satellite could hover.  This
result was first obtained by the eighteenth-century French
mathematician Lagrange; he also found that there were five positions in
all where a body could remain fixed with respect to both Earth and Moon
(Figure 18).  These are known as Libration points, and L, and L2, on
the Earth-Moon line, may one day be of great importance for lunar
communications.  (L3 is on the same line, but on the other side of the
Earth.) Incidentally, the position L, between Earth and

Moon, has nothing to do with the so-called neutral point, where the
gravity fields of the two bodies balance; that is a mathematical
abstraction with no physical significance.

L2 and L, (which is 36,000 miles from the Moon) are regions of
instability, so objects placed here would eventually wander away.  This
would be no problem for space stations, as the amount of thrust needed
to correct deviations would be very small.  L4 and Lti, known as the
equilateral, or Trojan, points, are more stable; in 1961 the Polish
astronomer Kordylewski claimed to have detected patches of light here
which may be due to accumulations of cosmic dust.  It may be worth
investigating these regions with space probes to see what kind of
celestial junk has accumulated on these moving ledges in the Earth-Moon
gravitational crater.

Moon

"Neutral>Rowint'06

L L5

Earth

Fig.  17.  Libration points in the Earth-Moon system.

THE LUNAR COLONY

In the last chapter it was mentioned that the cost of maintaining one
man on the Moon might be of the order of $50 million a year.  In the
face of such horrendous statistics, it may seem ridiculous to talk of
establishing large bases-and even, colonies-on the Moon.

But this is looking at the problem through the wrong end of the
telescope.

It would be more accurate to say that the huge cost makes it mandatory
to set up a lunar base, so that it becomes self-supporting in the
shortest possible time.  The present vast expense of lunar exploration
is largely due to the need to carry propellants for the round trip and
the fact that all expendables (food, water, air) must be supplied from
Earth.  The Pilgrim

Fathers would not have done too well if they had had to send the
Mayflower back to Europe when they became short of breath.

The future of lunar (and, as we shall see later, Solar System)
exploration therefore depends on our ability to find supplies of all
kinds on the Moon.

The most valuable substance of all-as it is on Earth, when in short
supply would be water.

It certainly exists on the Moon; the question is where, and in what
form.  The free, liquid state can be ruled out-at least near the
surface-but ice may occur under ground, for in caves where the solar
heat never penetrates, the temperature is always far below the freezing
point.  (Radio measurements indicate that only a few feet below the
surface the temperature is constant at perhaps degrees F.) There are
certain lunar formations-low Imes-which may indicate the presence of
permafrost.  At e other extreme, if there are local hotspots, or not
quite extinct volcanoes, steam may be available, as well as power and
useful chemicals.

These are the optimistic assumptions, which may be wrong.  If worse
comes to worst, it will be necessary to extract water from the minerals
in which it occurs; straightforward heating would be sufficient in most
cases.  During daytime, unlimited quantities of beat can be collected
by concave mirrors; however, the physical problem of handling the
amounts of rock involved would be formidable.

Since 'water is 90 per cent oxygen, the two major necessities of life
would be provided.  But the hydrogen would be almost equally important,
since this is the best of all rocket fuels.  Once it could be liquefied
and stored, the economics of Earth-Moon space transportation would be
revolutionized.

Beyond water and oxygen lies the much more complex problem of food.
Perhaps by the time (around the turn of the century?) we are planning
extensive lunar colonization, the chemists may be able to synthesize
any desired food from such basics as lime, phosphates, carbon dioxide,
ammonia, water.  In fact, this could be done now if expense was no
object; it will have to be done economically, within the next few
decades, to feed Earth's exploding population.

An obvious alternative is soil less or hydroponic, farming, already
widely used in locations where land is at a premium; it has also been
tried experimentally in the Antarctic and aboard nuclear submarines.
Yet another is algae culture; both systems of food production would be
ideally suited for the Moon, where there is fourteen days of unbroken
sunlight-and no bad weather.  The plants would not only provide food
but also would be an essential part of the life-support system,
regenerating oxygen and recycling waste products, just as they do on
Earth.

Another idea is more speculative, and I have yet to see it given
serious scientific study.  If it works, I am prepared to claim it as
original; otherwise I shall hastily disown it.

We may be able to develop plants which can grow unprotected on the
lunar surface; some desert-adapted forms on Earth give hints as to how
this may be done.

There is a small African cactus, popularly known as a 11 window plant,"
which is entirely enclosed in a tough spacesuit of skin, difficult to
cut even with a razor blade.  Having solved the problem of conserving
water, this admirable and ingenious organism then admits the equally
essential sunlight through a transparent windowpane.  (Perhaps, in a
few more million years, it may be the first plant to evolve an eye.)

With a little help from terrestrial geneticists, a lunar flora could be
designed; indeed, we may find one already there, which would save us a
great deal of trouble.  I am sure that I am not the only farmer's boy
who felt his fingers itch when he saw the good earth pushed up by
Surveyor I (Plate 57).

Though such speculations may seem premature at the moment, the rate of
buildup of the lunar bridgehead may depend upon concepts which today
appear no less fantastic.  Until we know just what is possible on the
Moon and what its natural resources may be, we cannot tell whether its
maximum future population will be a few score scientists occupying
temporary, inflatable igloos or millions of men living comfortable and,
to them, quite normal lives in huge, totally enclosed cities.  The
greatest technical achievements of the next few centuries may well be
in the field of planetary engineering, the reshaping of other worlds to
suit human needs.  We shall return to this theme in Chapter 25, but it
will already be apparent that the conquest of the Moon will be the
necessary and inevitable prelude to remoter and still more ambitious
projects.  Upon our own satellite, with

Earth close at hand to help, we will learn the skills and techniques
which may one day bring life to worlds as far apart as Pluto and
Mercury.

The Moon will not only be a training ground for the other planets; it
may be an essential stepping stone toward them.  Look again at the
energy diagram in Figure 6, showing the work necessary to climb from
the Moon, and from the Earth, up to the flat plateau of interplanetary
space.  Compared with the Earth, the Moon's surface is already 95 per
cent of the way to

Mars and Venus.  If rocket propellants can ever be manufactered
there-and this could be done simply by electrolyzing lunar water-it
could become the key to the Solar System.

Spaceships making any interplanetary journey would, on departure or
arrival, refuel there.  They would probably

'b

Plate 57.  One of the first photos of the Moon's surface, transmitted
by

Surveyor 1. (Surveyor's footpad is in lower left.)

Hughes Aircraft Company not land, but would orbit the Moon while
specially developed, short-haul tankers brought fuel (and other locally
produced supplies) up to them.

It would even be good economics to refuel, from the Moon, spaceships
that had just reached orbital velocity around the Earth and were
circling it outside the atmosphere.  Sending rocket fuel the
quarter-million miles from the Moon might well be cheaper than lifting
it the few hundred miles up from Earth.

This would be especially true if it could be dispatched to the point
where it was needed, without the combustion of vast amounts of
propellants.

Because the Moon has no atmosphere, the old Vemian concept of the
spac6gun is no longer a fantasy; the low escape speed "(5,000 mph, as
against the

EartYs 25,000 mph) also makes such schemes much more attractive.

One would not use a gun, of course, but a horizontal or gently rising
launching track, probably operated electrically.  It might be
impracticable to launch manned spacecraft by this means, because the
acceleration would be too high, unless the track was about a hundred
miles long.  But containers full of rocket propellant could be shot off
into space by a track only two or three miles long and intercepted near
the Moon, the

Earth, or even some other planet after a journey of a few months.
Perhaps one day the specialized products of the Moon's high-vacuum
industries will be dispatched to Earth by some such launching system

It it possible that major improvements in propulsion, especially the
development of nuclear rockets, will make such schemes unnecessary.
just how much room for improvement there is may be judged by one rather
striking fact that even scientists find it hard to credit.

As has been repeatedly stated, the problem of leaving the Earth and
traveling to another celestial body is one of energy, or work.  The
amount of energy needed to lift the, average man all the way to the
Moon is about 1,000 kilowatt-hours-which, if purchased from an electric
utility company, may cost only $10.  This should be compared with the
price of the first ticket to the Moon, which is approximately $10
billion, though in later

Apollo flights, as development costs are written off, it should come
down to something like $1 billion.

This billion-to-one inflationary factor is a perhaps exaggerated yet
not wholly unfair measure of our present ignorance and of the backward
state of the astronautical art.  I do not suggest that a ticket to the
Moon will ever cost $10 (after all, there will be a few expensive but
rather essential extras like life-support systems and navigational
equipment to be provided), but I do suggest that many of those
depressing zeroes will be slashed off as our technology improves.

It is generally considered that reusable boosters, which can be flown
(or parachuted) back to their launching site for further missions, are
an essential step in this direction.

0 I developed this concept in a paper entitled "Electromagnetic
Launching as a Major Contribution to Space Flight" (Journal of the
British

Interplanetary Society, November, 1950) and gave it rather wide
circulation in the short story "Maelstrom 11" (Playboy Magazine,
November, 1962).  In 1962 the idea was revived by William Escher of the
Marshall Space FUght

Center, who coined the term "lunatron" for such a launcher.

Certainly space travel can never be much more than an expensive, though
worthwhile, scientific venture if something like a Saturn 5 has to be
thrown away on every flight.  An Atlantic liner that delivered three
passengers and sank after its maiden voyage would not be an engineering
achievement of which one could be very proud.

Improvements in technology never merely add together; they multiply, as
the history of commercial aviation has shown.  That story will be
repeated in space; some of the advances which will make this possible
may be: reusable launch vehicles aerospace planes orbital rendezvous
with specialized spacecraft tailored for each stage of the mission;
refueling in orbit; refueling on the Moon; refueling from the Moon;
nuclear propulsion.  The last, and perhaps most important of all, will
be discussed in Chapter 24.

These are all things that can be anticipated, therefore, in accordance
with past lessons; we can be sure that the really revolutionary factors
are not on this list.  (Gravity control?  Matter transmission??  At
this stage, one guess is as good as another.) Nevertheless, the
exploitation of the foreseeable techniques to their limit could result
in truly commercial space transport being in sight by the end 4 this
century.  And perhaps fifty years from now, anyone should be able to
afford a visit to the Moon at least once in his lifetime-perhaps to see
grandchildren who, having been born under lunar gravity, can never come
to Earth and have no particular desire to do so.  To them it may seem a
noisy, crowded, dangerous, and, above all, dirty place.

It is strange to think that in a few more years any amateur astronomer
with a 'good telescope will be able to see the lights of the first
expeditions, shining where no stars could ever be, within the arms of
the crescent Moon.

Those lights will spread out over the new world, as they have covered
the old; and in a few generations more, they will sometimes be a little
hazy.

The features near the edge of the lunar disk will no longer appear so
crystal sharp in the telescopes of Earth; over the bitter protests of
the astronomers and the physicists, who must now look for a new home,
the Moon will be acquiring an atmosphere.

And two hundred years from now there will be committees of earnest
citizens fighting tooth and nail to save the last unspoiled vestiges of
the lunar wilderness.

IV.  AROUND THE SUN

THE TRILLION-MILE WHIRLPOOL

There are two ways of looking at the Solar System.  The first is purely
descriptive; it is the way that most astronomy books begin= the family
of planets, asteroids, satellites, comets, and meteoroids of which the
Earth is a small but hardly negligible member.  The second is dynamic;
it is concerned with energies and velocities and gravitational
fields-things which cannot be seen but which are as much the concern of
the new navigators as winds and currents and soundings were of the
old.

Even the descriptive approach presents difficulties, because the
Solar

System is built on such a scale that to most people the figures are
quite meaningless.  Moreover, it involves an acute disparity in size.
If we concentrate on the distances and try to reduce them to manageable
proportions, even the largest of the planets becomes a mere point.

Nevertheless, the effort should be made, for no man can call himself
educated if he has no conception of the universe in which he lives.
There are still primitive peoples to whom a hundred miles is an
inconceivably great distance; yet there are also men who think nothing
of traveling ten thousand miles in a day.  As speeds of transport have
increased, so our sense of distance has altered.  Australia can never
be as remote to us as it was to our grandfathers.  In the same way,
one's mental attitude can adapt itself to deal with interplanetary
distances, even if the mind can never really envisage them.  (And,
after all, can the mind really envisage a thousand miles?) The first
step in this "familiarization procedure" is the 241

scale model.  To begin with, let us concentrate on Earth and Moon
alone, ignoring the other planets.  We will take a scale on which a man
would still be visible to the naked eye, our reduction factor being
1,000 to 1. The

Earth is now a sphere 8 miles in diameter, and 240 miles away is
another sphere, the Moon, 2 miles across.  On this scale a human being
would be a little less than one-twelfth of an inch high, the speed of a
subsonic airliner would be half a mile an hour and that of an orbiting
spacecraft about 18 miles an hour.  The twelfth-of-an-ineb-high man
contemplating the gulf between Earth and Moon is thus in much the same
position as an intelligent ant trying to picture the size of England or
Pennsylvania.

To bring in the planets, we must alter the scale again, making the man
sink far below visibility.  With a reduction of a millionfold, the
Earth is now 40 feet in diameter, the Moon 10 feet across and a quarter
of a mile away.

The Sun is 93 miles away and almost a mile across; 36 and 67 miles from
it, respectively, circle Mercury and Venus.  Mercury is 15 feet across,
Venus 38-a little smaller than the Earth.  Beyond the Earth's orbit is
Mars, 20 feet in diameter and 140 miles from the Sun.  It is
accompanied by two tiny satellites, only about half an inch across.

Outward from Mars is a great gulf, empty save for thousands of minor
planets, or "asteroids," few of which on this' scale are much larger
than grains of sand.  We have to travel 483 miles from the Sun-340
beyond Marsbefore we meet Jupiter, the largest of all the planets.  In
our model it would be over 400 feet in diameter, with twelve satellites
ranging in size from 15 feet to a few inches across.

You may feel that our model is getting somewhat unwieldy despite our
drastic reduction of a million-to-one, but we are still nowhere near
the limits of the Sun's emoire.  There are four more planets to
come-Saturn (diameter 350 feet), Uranus (150 feet), Neptune (160 feet),
and Pluto (20 feet).  And Pluto is 3,700 miles from the Sun.

This model of our Solar System shows very clearly the emptiness of
space and the difficulty of representing on the same scale both the
sizes of the planets and the distances between them.  If we reduced the
Earth to the size of a table-tennis ball, its orbit would still be half
a mile across, and

Pluto would be 10 miles from the Sun.

S.clurn j pit.,

Pluto Neptune Uranus 0 1,000

Orbits of the outer planets Milli- fury

The Asteroids :(~Guv_

Jupiter Mo.  Orbits of the inner planets ~f W1.

M 7c7rth Neptune plo

Venus Mors ..0 ~to

Uranus

Jupiter Saturn The planets and their satellites Think of mil"

Fig.  18.  The Solar System.

A pictorial attempt to show the planets, their satellites, and their
orbits to the correct scale is given in Figure 19 Even in the most
"magnified" of the diagrams, however, it is not possible to represent
the smaller satellites accurately.

Three other points remain to be mentioned before our picture of the
Solar

System is complete.  In the first place, it is nota stationary affair.
All the planets are moving, and in the same direction around the sun.
The innermost planet, Mercury, takes only 88 days to complete one
revolution, while Pluto takes 248 years so that astronomers will have
to wait until

A.D. 2178 before it returns to the part of the sky where it was
discovered in 1930.

The second important point is that almost all the planets lie in or
very near the same plane, so that the Solar System is fairly flat.
There are exceptions to this rule, the worst being Pluto, whose orbit
is inclined at an angle of 17 degrees to that of the Earth's; but on
the whole it is well obeyed, and it greatly simplifies the problem of
interplanetary navigation.

Finally, the shapes of the orbits.  They are very nearly circular, with
the

Sun at the center.  Only Mercury, Mars, and-once again-Pluto depart
seriously from this rule, their orbits being appreciably elliptical.
That of Pluto, in fact, is so eccentric that after 1980 the planet will
be, for some decades, inside the orbit of Neptune and will no longer
mark the frontier of the Solar System.  It is, of course, possible that
there are undiscovered planets beyond Pluto, and certainly many comets
travel out to vastly greater distances from the Sun before it draws
them back.

All these bodies, from gigantic Jupiter to the smallest speck of
meteoroid al dust, are entirely controlled by the gravitational field
of the

Sun, exactly as the Moon and today's halo of artificial satellites are
controlled by the Earth's field.  We see in the Earth and Moon a small
version of the Solar System itself; Jupiter and Saturn provide even
more impressive models, as each has more moons than the Sun has
planets.

The dynamics of the Solar System can thus be understood by once again
invoking the imaginary "gravitational crater" used to explain the
movement of the Earth satellites (Chapter 6).  It will be remembered
that the Earth's field could be represented by a crater 4,000 miles
deep, around whose upper slopes circles the Moon with its own much
smaller-180 miles deep-crater let (Figure 6).  All possible orbits on
the Earth-Moon field can be reproduced by the movements of a smooth
object rolling along the inside of this surface.

Because the Sun's gravitational field is so much more powerful than
the

Earth's, the corresponding model is also far bigger; using the same
scale as before (the work done to leave Earth being equivalent to a
4,000-mile climb), the Sun's field must be represented by a crater
about 12 million miles dee pl In other words, it is 3,000 times harder
to escape from the Sun than from the Earth.

Luckily this is not our problem; we do not have to climb all the way
out of the Sun's gravitational crater, as well as the Earth's.  But in
moving across the planetary orbits, we do have to travel up and down
the far-ranging solar field; so the location of the Earth and planets
on its outer slopes is of vital importance.

When we look into this matter, we discover something that could never
have been guessed from the purely descriptive map of the Solar System
which has just been given (Figure 18).  This shows the inner planets
crowded around the Sun, with the outer worlds at progressively
increasing distances, out to almost 4 billion miles.

The "energy diagram" of the Solar System, however, presents a
completely different picture.  Far from being near the Sun in the
gravitational sense, even the innermost planet, Mercury, is very remote
from it.  Whereas the full depth of the imaginary crater is 12 million
miles, all the planets are crowded together on its uppermost slopes,
within 150,000 miles of the rim.

This is indeed fortunate for the future of astronautics; the planets
are 99 per cent free of the Sun's gravitational field, and moving
between the different orbits requires only a small fraction of the
energy that it might well have done.  It is easy to imagine solar
systems in which the planets are much more tightly gripped by gravity,
and the energies of chemical fuels would be utterly inadequate for
transfer from orbit to orbit.  But in our case it takes less energy to
cross the immense spaces between Earth and Mars than the relatively
trivial distance between Earth and Moon.

In other words, the Sun's gravitational field, though of enormous
extent, is very "flat" in the region of the planets, and the climb up
its slope requires relatively little energy.  But superimposed on this
field are the much smaller fields of the individual planets; they are
effective only over very short distances, astronomically speaking, but
their slopes are very steep.  Hence the paradox that the first thousand
miles of an interplanetary journey usually requires more energy than
the next hundred million.

To give some idea of the values involved, Table 7 lists the depths of
the gravitational craters for the Sun and major planets, as well as the
velocities needed to escape from them and to orbit them.

It will be seen that the energy values vary so enormously that it is
impossible to show them on a single diagram, but in any case the
figures that are of most direct interest are the respective velocities
of escape.

These also cover a smaller and more easily handled numerical range, so
they have been used to construct Figure 19.

This map of the Solar System bears little resemblance to the
conventional representation in the astronomy books, but it is much more
useful to astronauts.  It shows how difficult it is to land on the
giant planets and how relatively easy it is to move between the inner
ones.  Of course,

TABLE 7

PLANETARY GRAVITATIONAL FIELDS

ORBITAL ESCAPE

DEPTH OF GRAVITATIONAL VELOCITY' VELOCITY

BODY CRATER AT I G, MILESMPHMPH

Sun 12,000,000 980,0001,380,000

Mercury 5606,6009,300

Venus 3,700 17,00024,000

Earth 4,000 17,50024,600

Moon 180 3,7005,300

Mars 850 8,00011,400

Jupiter 120,000 95,000135,000

Saturn 42,000 57,00081,000

Uranus 16,000 35,00050,000

Neptune 20,00040,00056,000

Pluto 3,000?  15,00020,000

Miles 0 10,000,000100,000,000 1,000,000,000Infinity

Pluto

Neptune

Uranus -100,000 Mars

Earth Saturn

Venus -200,000 Mercury Jupiter

-300,000

Pluto

N.

' ptun.

Zrs Urrnu,

To Sun 1,400,000 mph

Fig.  19.  The gravitational field of the Sun.

this diagram is only static and must be used with caution; the planets
are all moving around the rim of the solar crater at velocities ranging
from over 100,000 mph for Mercury to a mere 10,000 mph for Pluto.  All
these velocities must be taken into account when actual voyages are
planned; as we shall see later, they can be used to good advantage.

So let us now try to animate this static model by an act of
imagination.

Picture an immense whirlpool-12 million miles deep- whose funnel is
almost vertical for millions of miles, but at last flares out toward
the horizontal, where it merges into an infinite ocean.  On the upper
slopes of this great maelstrom, at distances below the surface ranging
from 2,000 to 150,000 miles, are much smaller whirlpools, circling
independently at almost constant levels; their own depths vary from a
few hundred (Mercury) to more than a hundred thousand miles (Jupiter).
Naturally, the lowest one has to move swiftly to avoid being sucked
down in the greater abyss; the outermost one can maintain itself by
moving at a much more leisurely pace, far out on the slowly circling
rim.  There is, of course, no definite limit to the extent of this
gravitational vortex; its influence reaches out to at least a trillion
miles from the Sun, and at still greater distances it merges
imperceptibly into the combined field of all the other stars in the
universe.

Our Earth is at the bottom of the third little whirlpool from the
center; a smaller vortex, the Moon, circles very close to it. Scattered
up and down the greater slope are the moving whirlpools of all the
other planets, passing and repassing each other at their different
levels.  Until our time, nothing, so far as we know, has ever traveled
from one to another.

The whole immense system is perfectly stable.  It was set spinning
billions of years ago, and there is every reason to suppose that its
future may be far longer than its past.

On completing the above paragraphs, I was suddenly smitten with the
familiar sense of d9ja vu.  For once, it did not take long to identify
the cause:

And now, concentric circles seized the lone boat itself, and all its
crew, and each floating oar, and every lance-pole, and spinning,
animate and inanimate, all round and round in one vortex, carried the
smallest chip of the Pequod out of sight.

Our "lone boats" should fare somewhat better when they venture forth
into the vortex of the Sun, for it does not seem likely that Captain
Ahab would ever have survived a NASA selection board.

PATHS TO THE PLANETS

If our spacecraft possessed unlimited sources of energy, we could fly
to any planet in a straight line whenever we pleased.  But as this is
far from the case, and indeed it taxes our skill to the utmost merely
to escape from the

Earth, it is clear that for a very long time to come all planetary
voyages will follow the most economical paths.

The approximate shapes of those paths should be intuitively obvious to
anyone who has grasped the analogy of the great solar whirlpool,
sweeping the planets around it at their various levels and speeds.  The
easiest "transfer orbit" from one level to another will be one that
grazes both; this was proved in the late 1920's by Dr.  Walter Hohmann,
and these paths are now known as Hohmann orbits.  *

Figure 20 shows the situation for the two cases of most immediate
interest-the journeys to Mars and Venus.  (The orbit of Mars is quite
elliptical, but for simplicity it is shown as circular, and average
values are given).  The Earth is moving at 66,000 mph along its orbit,
Mars at only 54,000 mph at its considerably greater distance from the
Sun.  If a rocket had just sufficient energy to escape from the Earth,
it could continue to move along an orbit identical with Earth's; but if
it were given an additional boost, it would start to drift outward from
the Sun.

a Hohmann published his results in a book entitled The Attainability of
the

Heavenly Bodies ( 1925).  He was the chief architect of the city of
Essen, and died with it in 1945.  Now Essen has been rebuilt, and
Hohmann has at least a specialized immortality.

Mors 54,000 mph

48, mph 84,000 mpva Venus a, 78,000 mph 84,0 mph

7 00 mph

Sun LO 3\\ 1 /x 0_

Sun

1000)

Earth ph 1000 m (Cb)6),000 In 073,000 mp hEarth 66,000 mph (a)

Fig.  20.  Hohmann orbits to Mars and Venus.

Calculation shows that an extra 7,000 mph would be just sufficient to
take it out to the orbit of Mars, which it would graze on the other
side of the

Sun-exactly opposite the point where it received its original
impulse.

However, when it reached this point it would not be moving swiftly
enough to sustain itself there.  Its velocity would now have dropped,
as a result of climbing up the Sun's field, to only 48,000 mph, and it
would need another 6,000 mph to keep pace with Mars.  So a second
impulse would be necessary; otherwise it would fall back to the Earth's
orbit along the other half of its transfer ellipse.

For a voyage to Venus, just the opposite procedure is necessary.  A
rocket already moving in the Earth's orbit has to lose speed to drop
Sunward-and it has to lose still more to remain in the orbit of Venus.
This does not necessarily mean that it is easier to get to Venus than
to Mars; in space, it is just as difficult to lose velocity as to gain
it.  The change of speed is all that matters, as far as fuel
consumption is concerned.  The only exception to this rule is when
there is a convenient atmosphere where excess velocity can be disposed
of by air braking.

Of course, if only a "fly-by" is needed, as in the case of a Mariner
reconnoitering Mars, it is unnecessary to match velocities at the
destination; once its job is done, the probe can race on past the
planet and continue along its elliptical orbit around the Sun.  But if
it is desired to drop a landing vehicle, conduct an orbital survey, or
set human explorers down onto the surface, then a rendezvous with the
planet has to be made by the use of rocket propellants, atmospheric
braking, or both.

When we look more closely into the problem of launching a rocket away
from

Earth and injecting it into a transfer orbit to another planet-say,
Mars-a rather subtle point in energy conservation arises.  At first
sight it would seem that the velocity the rocket must achieve for the
mission can be obtained by simple arithmetic: 25,000 mph is needed to
escape from the

Earth; 7,000 mph is needed to enter the voyage orbit-therefore, a total
of 32,000 mph is required.

Luckily, it is much easier than this; 32,000 mph would be needed if the
mission were carried out in two separate stages-if the rocket first
escaped from Earth, drifted away a few million miles until it was
effectively outside its gravitational attraction, and then reignited
its engines to leave Earth's orbit and head for Mars.  But this would
be a ridiculously wasteful procedure; it would mean lifting all the
fuel for the Mars transfer out of the Earth's gravitational field
before it was burned.  It makes far more sense to burn all the fuel
that is necessary in a single impulse, as close to the Earth as
possible, and then to let the spacecraft coast to its destination,
apart from any minor navigational changes that may prove necessary.

When the mission is recalculated on this basis, the initial velocity
needed turns out to be not 32,000 mph but a mere 26,000 mph-only 1,000
mph more than the velocity of escape itself.  At first sight we seem to
have got something for nothing, but this, needless to say, is an
illusion.  The single impulse, applied as close to the Earth as
possible, is so much more efficient that it produces the same final
result as the two separate ones.

Exactly the same argument applies at the other end.  We could speed up
to match the orbital velocity of Mars, which requires an extra 6,000
mph.

Then, in a separate maneuver, we could fall into the gravitational
field of

Mars, acquiring another 11,400 mph (the Martian escape velocity) in the
process, which would have to be neutralized before we approached the
surface.  Total velocity bill: 17,400 mph.

But doing everything in a single maneuver, as close to

Mars as possible, cuts the bill to about 12,000 mph another substantial
saving.  Table 8 sums up the situation by recapitulating the two ways
of achieving the same result.

TABLE 8

EARTH-MARS MISSIONS

(WITH IAN DING

FOUR-IMPULSE MISSION MPH

2. Transfer to voyage orbit 7,000 3. Matching Mars orbit 6,000 4. Mars
landing 11,400

Total 49,200

TWO-IMPULSE MISSION MPH

1. Earth escape and transfer to voyage orbit 26,000 2. Transfer to Mars
orbit and landing 12,000

Total 38,000

These figures assume the Mars landing is made entirely by rocket
braking and are therefore unrealistically high.  It appears certain
that, thin though it is, the Martian atmosphere is admirably suitable
for re-entry purposes (though in this case, the word re-entry is hardly
appropriate).

The final touchdown may require a small amount of rocket braking, but
almost all the 11,400 mph of approach speed can be destroyed by air
resistance.  This would reduce the total impulses needed for the two
missions to about 38,000 and 27,000 mph respectively, leading to the
remarkable result that it is much easier to make a one-way trip from
Earth to the surface of Mars than from Earth to the surface of the
Moon.

The Hohmann, or minimum-energy, orbits have two serious disadvantages,
at least as far as manned space travel is concerned.  Like the easiest
road up a mountain, they take the longest way around, and therefore the
saving in fuel has to be paid for in time.  The Venus journey lasts
about 145 days; that to Mars is rather longer, about 260 days.

It is also obvious that such voyages can take place only at rather
infrequent intervals, when the planets are in the correct positions
with respect to each other.  The moment of departure of the spacecraft
has to be calculated so that when it has completed its serniellipse
around the Sun, it makes its appointment with its target planet.
Although a certain amount of latitude is possible, the fuel penalty
involved in missing a launch date increases rapidly with time.

The situation is even more complicated when return journeys are
considered, since it is then necessary to wait for a second suitable
planetary configuration.  For this reason a voyage to Mars and back
along Hohmann orbits would last approximately 970 days.  The journey
time would be twice 260, or 520 days; the remaining 450 days would be
spent on Mars, waiting for the planets to get into the right position
for the return trip.  So the "cheapest" orbits may not be the most
practical ones in reality, especially for manned expeditions.

When journeys to the outer planets are considered, the voyage times
along

Hohmann orbits become even more intolerable; one way to Jupiter would
be 2 years, 9 months, and the round trip to Pluto would take just under
a centuryl It will therefore be necessary to use much more direct and
far more expensive trajectories when such journeys are seriously
planned; only the use of nuclear power for propulsion will make them
possible.

Some typical high-speed (and high-cost) orbits are shown in Figure 21.
If a body is moving around the Sun at a moderate speed, like a planet
or a comet, it travels along an ellipse.  If it is moving so fast that
it will eventually escape from the Solar System, its path is the open
ended curve known as the hyperbola; both types are shown in Figure 21. 
Given unlimited propulsive ability, a spaceship could choose whichever
of these orbits was the most convenient and travel from planet to
planet at any time, without waiting for a suitable configuration.

In this way transit times could be cut down to a few weeks or even a
few days.  Unfortunately, the energies needed for such missions would
be enormous (hundreds of times greater than for Hohmann trips), since
the orbits do not utilize the existing planetary velocities, but
instead partly cancel them out.

These problems are well illustrated by the case-not as theoretical as
it seems-of a rocket launched to the Sun.

Fig.  21.  High-speed orbits around the Sun.

The distance is relatively small, but the fuel requirements are very
great, for it is necessary to cancel the whole of the Earth's 66,000
mph of orbital speed.  Only then can the probe drop directly toward the
Sun; if it has any sideways (orbital) velocity at all it will miss the
Sun, go around it in a tight hairpin bend, and continually retrace a
very thin ellipse stretching back to the orbit of Earth (Figure 22).
Getting to the Sun is therefore very difficult indeed though it will
certainly be attempted with instrumented probes, which could be
designed to withstand entry into the solar corona.

The time of free fall from Earth to Sun is only 65 days.

After these theoretical discussions, let us now look at some actual
achievements.  The first object of any size to escape from the Earth
was the

Soviet Union's Luna I ("Mechta," or "dream"), aimed toward the Moon on
January 2, 1959.  It passed within 5,000 miles of the Moon, whose
gravitational pull changed its direction of motion slightly but made
very little difference to its speed.  Then, having lost almost all its
initial launch velocity escaping from Earth, it continued to drift
slowly on into space.

But that "slowly" is a relative term.  There is no such thing as
-absolute speed in space, as was realized long before the time of
Einstein.  Some convenient marker, or

There is, however, a way of doing it even today; see page 259.

reference system, is always assumed, though not always explicitly
mentioned.

In the initial stages of an interplanetary voyage, the reference point
is the Earth; later it is the Sun; and, finally, it is the planet of
destination.

When it was a million or so miles out, Meebta had lost through gravity
drag almost all the 25,000 mph its rockets had given it relative to its
launch pad.  But that launch pad was moving around the Sun at the
respectable speed of 66,000 mph, and Mechta still had the whole of this
velocity, plus the small change of a few hundred miles an hour left
over after it had achieved escape.  Thus the laws of celestial
mechanics constrained it to move in an orbit very similar to the
Earth's, but because of its slight speed excess, it swings out almost
halfway to Mars at its far point.  The actual figures for Mechta's
orbit are: perihelion 91 million miles; aphelion 123 million miles. And
because its orbit is larger than Earth's, it takes longer to complete
one revolution, 443 days.

After fifteen months, therefore, Mechta came back to its original
launch point at the orbit of Earth, but, of course, Earth was no longer
there, having pulled a good many million miles ahead on its quicker,
twelve-month orbit.  However, after a sufficient number of revolutions,
the natural planet and the artificial one can get together again.  The
ratio of the two periods-443 and 365 days-is almost exactly 11 to 9; in
other words, 11

Earth years equal 9 Mechta "years."  So about 1970, 1981, and so on,
Meebta should be in the vicinity of Earth, but since its radio is long
since dead, it is most unlikely to be detected.

This simple calculation ignores some essential facts, which must be
taken into account when planning any space voyage.  The Solar System is
not really flat, and the planetary orbits are inclined to each other at
small angles.

Mechta's orbit is tilted to Earth's at about one degree, which may not
seem a great deal, but is enough to ensure missing an appointment by a
good many hundred thousand miles.  These orbital inclinations have to
be allowed for by a suitable mid-course correction when a planetary
encounter is attempted.

The first such encounter took place on May 19, 1961, when a space probe
launched three months earlier from the Soviet Union's Earth-orbiting

Sputnik 8 passed within 62,000 miles of Venus.  However, radio contact
was lost immediately after departure from Earth orbit, so the mission
was a failure-as had been the case with two earlier and unannounced
attempts to reach Mars in October, 1960.

Several further Russian launches, to Mars and Venus, were no more
successful, though the elaborately instrumented Mars I passed within
120,000 miles of its intended goal on June 19, 1963.  Unfortunately,
radio contact was lost at about 66 million miles from Earth.

By that time the United States had already scored its first major
scientific success in deep space, with Mariner 2, which passed within
22,000 miles of Venus on December 14, 1962, after a voyage lasting 149
days The first physical contact with Venus, or with any other planet,
was made by the Russian Venus 3 on March 1, 1966, when a capsule of
instruments was dropped into the atmosphere.  But once again the
scientists were unlucky, as radio communication with the probe had been
lost some time before impact.

The first Mariner launch to Mars (Mariner 3, November 5, 1964) met with
a fate not quite as ignominious as that of Mariner 1. Its protective
shroud collapsed under the aerodynamic forces acting on it during the
ascent, and

Mariner 3 was pinned captive inside, unable to extend the solar panels
upon which it depended for energy.  It died of electrical starvation
within a few hours.

For the jet Propulsion Laboratory's engineers, it was literally a case
of

"Back to the old drawing board," and by prodigious efforts a new shroud
was designed, fabricated, and tested before the Mars "launch window"
closed again.  Mariner 4 was ready within three weeks and took off for
Mars on

November 28, 1964.  (The indefatigable Soviets followed two days later
with

Zond 2, but once again they lost contact in mid-mission.)

The path of Mariner 4 (Figure 22) was a fairly close approximation to
a

Hohmann orbit.  The space probe had somewhat more than the minimum
speed requirement and got to Mars in only 227 days instead of the
optimum 260.

This involved no great penalty, as what was desired was an encounter,
nota rendezvous.  After a mid-course correction, Mariner 4 passed
within 6,000 miles of Mars on July

Mariner 1, launched on July 22, 1962, was wrecked by the most expensive
hyphen in history.  Omission of a single "2' from the program fed to
its guidance computer sent it off course, and the Atlas-Agena booster
had to be deliberately destroyed.

Mors at launch

Earth at launch (Nov.  28, 1964)

Sun

0 2P 40 60 So too

Milli n miles

0 Earth at encounter

Mon encounter (July 14, 1965)

Fig.  22.  Orbit of Mariner 4.

14, 1965, exactly as intended.  It radioed back nineteen photographs,
as well as a great deal of scientific information, which changed many
existing ideas about the nature of Mars (Chapter 22).

An example of a more advanced Mars mission, of a type which might be
flown by manned spacecraft in the 1970's, is shown in Figure 2V

This would allow of an encounter with Mars, during which time the
planet could be studied from close range for many weeks, and from a
distance of only a few hundred miles for several hours.  Landing probes
could also be dropped, to radio back information to the passing ship,
or directly to

Earth at a much lower rate.  The flight would continue on through the
inner asteroid belt, and the spacecraft would return to Earth after a
voyage of a little less than two years, re-entering by atmospheric
braking.

As for as propulsion requirements are concerned, this mission is much
easier than the Moon landing; operationally it is also simpler.  It
could therefore be carried out by existing vehicles, except for the
fact that even the most dedicated astronauts could hardly be expected
to endure

Apollo-sized quarters for two years.  So it will be necessary to
develop considerably larger spacecraft, as well as much t From E. Z.
Gray and Franklin P. Dixon, Manned Expeditions to Mars and

Venus.  Fifth Goddard Memorial Symposium, Washington, D.C."  March,
1967.  .....................-,-,.-...-,-,.".".".-..* .................
Mars flyby (Jan.  23, 1976)

Height: 200 miles

Speed: 21,000 mph

Leave Earth (Sept.  5, 1975)

Arrive Earth (July 18, 1977)

Fig.  23.  Mars fly-by mission.

more reliable life-support systems, before such flights are
attempted.

Exactly similar missions to Venus are possible, and indeed a little
easier; the initial speed needed for all these flights lies in the
range 27,000-28,000 mph, which is only 10 per cent more than that
needed to escape from Earth.  (Compare this with the more than 35,000
mph needed for the Apollo mission, when the lunar landing and takeoff
are added in.)

Moreover, by choosing times carefully and using a little midcourse
correction, it is possible to plan flights which include encounters
with both Mars and Venus in a single mission.

The most favorable dates for some possible "flybys are given in Table
9.

The one to aim for is obviously December, 1978; let us hope that we are
ready for it.  There are a great many scientists who would very
willingly give two years of their lives for a trip to 'both of our
nearest neighbors in space, even though they would spend only a few
hours in their vicinity.

Beyond Venus and Mars, the next targets in order of distance are
Mercury, the Sun, and the giant planet Jupiter.  The last is the
easiest and perhaps most exciting

TABLE 9

MARS AND VENUS FLYBYS

VOYAGE DURATION, DAYS

LAUNCH DATE OUTWARDRETURNTOTAL

Mars Sep.1975130537667

Oct.: 1977145533678

Nov."  1979132554686 Venus Jun.,1975117250367

Jan."  1977117257374

Aug.p 1978116249365

Apr."  1980109250359 Venus-Mars Dec.,1978142; 230253625

target, demanding a launch velocity of about 32,000 mph.  In this case
the problem is not getting to Jupiter, but transmitting useful
information back across a distance of half a billion miles.

It was difficult enough to receive Mariner 4's Martian photographs; the
transmission of each frame took eight hours, over a distance of 134
million miles.  An EarthJupiter'Pink would be three to five times
longer, and since radio-power requirements increase with the square of
the distance, a

Mariner might require a week to send a single picture back from
Jupiter.

Obviously, much more powerful transmitters are needed, and they will
have to operate from nuclear sources, as the rapidly weakening solar
rays cannot provide useful energy beyond the orbit of Mars.

NASA's Office of Space Science and Applications has prepared an
interesting study of a 500-pound space probe which could be launched to
Jupiter by a vehicle based on the now relatively modest Atlas-Centaur.
The flight would last about 600 days, going across the orbit of Mars
and through the asteroid belt.

After the fly-by, the trajectory of the probe would be greatly modified
by the enormous gravitational field of Jupiter.  We could use this to
good effect in at least three ways (Figure 24).

In case (a), the probe passes over one of the Jovian poles, and so its
orbit is deflected right out of the plane of the Solar System; in the
diagram it must be thought of as rising out of the paper, or plunging
into it.  In each case, a wholly unfamiliar region of space would be
explored.

Escape from

Solar System of High-inclination orbit (5-year period) Vs 16 man
~*i*i*

Sun

Earth at 31 Mo launch

Fig.  24.  Orbit of Jupiter probe.

In case (b) the probe would sweep on past Jupiter and in doing so would
acquire some of the planet's orbital velocity, as explained in Chapter
24.

As a result of this "byperboli.c encounter," it, could, in fact, gain
so much speed that it would escape from the Solar System completely and
head on out into galactic space, continuing to send back information
until it was perhaps a billion miles from Earth, or beyond the orbit of
Saturn.  The limiting distance would be set purely by the power of the
onboard transmitter and the size of the receiving antennas on Earth.

Case (c) is perhaps even more interesting and useful.  This time
Jupiter's gravity would be used to cancel the probe's orbital speed, so
that it fell directly toward the Sun, which it would reach about
sixteen months later.

Its instruments could thus give a cross-section of the Solar System all
the way from Jupiter into the Sun, and at a high rate of data
transmission, since the ranges involved would be relatively short (only
100 million miles).

Thus, by using Jupiter we can perform missions which are otherwise
quite impossible.  The direct route to the Sun takes only two months,
but even the 3,000-ton Saturn 5 could not send a useful payload along
it.  Yet, if we are content to take four years on the trip-which is
itself an advantage for a data-collecting space probe-a launch vehicle
in the 200-ton class will suffice.

Space is full of subtleties and surprises.  It is hard to believe that
the rocket that put John Glenn into orbit could also serve to send a
payload to the Sun-or to Proxima Centauri.

CHILDREN OF THE SUN

For a long time to come it is going to be very risky to write anything
about the planets.  After decades in the doldrums, planetary astronomy
is undergoing a total revolution; more has been learned about Earth's
neighbors in the last few years than in all previous history.  But this
is merely a modest beginning, the prelude to the real breakthrough,
which will be brought about by orbiters, landers, and, ultimately,
manned expeditions.

It must not be thought that space probes are responsible for all the
great advances of the last few decades; except in a few dramatic
instances, they have not yet contributed a great deal.  Most of our new
knowledge has come from ground-based techniques-interplanetary radar,
electronic devices to amplify and analyze the images seen through
telescopes, or improvements in spectroscopy.  Far from being obsolete,
giant telescopes are being built in greater numbers than before, and
they still have several generations of work ahead of them before they
become training aids for young graduate astronomers on their way to the
lunar observatory..

For reasons which are still unknown, the planets appear to form two
quite distinct classes.  On the one hand are the relatively small solid
bodies like the Earth, Mercury, Mars, Venus, and Pluto.  These range in
size from 8,000 miles in diameter downward, and all have a density
several times that of water.  They can probably be called terrestrial
type planets, and they probably consist of much the same

Plate 58.  Mars, Jupiter, Saturn, and Pluto.  First three photographed
with 100-inch telescope; Pluto with 200inch telescope.

Mount Wilson and Palomar Observatoies materials as does the Earth
(though it may be unsafe to generalize about

Pluto, concerning which practically not bing is known except its
diameter).

Forming a complete contrast are the giant planets

Jupiter, Saturn, Uranus, and Neptune.  The smallest of these has four
times the diameter of Earth, but their densities are extremely low (in
the case of Saturn, being actually less than that of water).  We are
forced to conclude from this that the four giant planets are partly
gaseous or liquid, perhaps possessing solid cores only at great depths
below immensely thick atmospheres.

The two types of planets are divided by a kind of no-man's-ldwd thinly
populated by thousands of asteroids, or minor planets, whose diameters
range from 480 miles down to a few yards.  Most of the asteroids-an
unfortunate word, as it means literally small star, and nothing could
be less starlike-occupy a broad, diffuse belt between Mars and Jupiter,
but some wander as far afield as

Saturn, while others plunge even nearer the Sun than Mercury.  At one
time it was thought that they were fragments of an exploded planet; now
it seems more likely that they are some of the general debris left over
from the formation of the Solar System.

To complete the picture, mention should be made of the comets, those
huge, tenuous clouds of gas which for thousands of years have terrified
mankind by their portents in the sky.  They travel around the Sun in
orbits which are often very eccentric and highly inclined to that of
the Earth.  Many seem to have a small, solid core, or nucleus,
generally believed to be made of frozen gases which expand in
spectacular eruptions as they near the Sun.

Though very little is known about the physical nature of comets, it is
only a matter of a few years before a probe is launched through one as
it comes near the orbit of Earth.

Two or three times in every century a comet is bright enough to be seen
in broad daylight (as happened with Ikeya-Seki in 1965).  But every
year, for months on end, one of the planets is brilliant enough to be
seen in the daytime if one knows exactly where to look for it.  This is
Ear tVs enigmatic sister-world Venus.

At her closest, she is only i5 million miles away, or five months as
the space probe flies.  Through the telescope she appears as a
dazzling, featureless crescent, with no trace of the surface detail
that makes the

Moon and Mars so endlessly interesting.

In size Venus is almost a twin of Earth; her diameter is about 4 per
cent smaller, and as a result her surface gravity is 10 per cent
weaker-a reduction that would hardly be noticed.  But here the
resemblance between

Earth and Venus virtually begins and ends, though astronomers have been
reluctant to accept this fact, until it was forced upon them by the
overwhelming weight of evidence.

The cause of the planet's brilliance has also been responsible for our
almost total ignorance about Venus.  She is covered with an
impenetrable layer of clouds, the composition of which has long been
another major mystery.  The obvious explanation is that they are
composed of water; but for a long time ground-based spectroscopes
failed to reveal any trace of it.  So alternative theories were
proposed; according to one, the clouds were huge dust storms, stirred
up by continual gales raging between the hot and the cold sides of the
planet; according to another, they were composed of formaldehyde, which
led to the comment that Venus was not merely dead, but pickled.  At
various times astronomers also advocated lakes of petroleum and seas of
soda water-the latter theory inspired by the one certain fact about the
planet's atmosphere, that it contains vast quantities of carbon
dioxide.

What made progress difficult was that even the length of the Cytherean*
day was totally unknown; since no surface features (or even persistent
clouds) could be detected, there was no way of measuring the planet's
rotation.

Guesses ranged all the way from 24 hours up to the full length of the
year-225 days.  Ironically, no one even dreamed of the truth, and it
was a great surprise when, in 1965, radar observations showed that
Venus rotated once in every 243 Earth days-and in a reverse direction
to the usual planetary spins.  Venus's day is therefore longer than its
year-a situation unique in the Solar System.

Analysis of the returning radar signals has also hinted at the
existence of mountain ranges, and attempts have been made to construct
the first crude maps of the hidden surface.  However, this task can be
carried out properly only by radar equipment just above the cloud
layer, in orbiting spacecraft.

This will be one of the next orders of business for Venus.

Because it receives about twice as much sunlight as the Earth, it is
obvious that Venus must be hot; just how hot has come as another (and
unpleasant) surprise.  In the 1950's measurement of the faint radio
waves emitted by the body of the planet indicated a surface temperature
of several hundred degrees, but many astronomers found it hard to
believe this.  They were forced to accept the verdict when the
instruments aboard

Mariner 2, detecting the very short radio waves from below the cloud
level, showed that the surface temperature must average about 800
degrees

Fahrenheit.  The maximum value at the long, hot noon must be well over
1,000 degrees.  It is difficult to imagine a more forbidding place; and
to make matters worse, the pressure at the bottom of the dense
atmosphere a The adjective for the planet Venus presents grave
linguistic problems.

"Venusian" is unacceptable to purists; "Venerean" raises false
expectations; "Cytherean" is correct but no one except classical
scholars understands what it means.  Take your choice.

must also be very high, perhaps equal to that a quarter of a mile down
in our oceans.t

It is, perhaps, a relief to abandon this exasperating planet and turn
to

Mars, where we are not confronted with impenetrable clouds; we can see
the actual surface of the planet and can make maps of its main
features.  Moreover, when it is nearest to us, Mars turns its
illuminated face full toward the Earth, unlike Venus, who passes
between us and the Sun on such occasions and is thus completely
invisible.

Despite these advantages, our knowledge of the planet is full of gaps,
and there are rival interpretations even of the admitted facts. Because
of its distance, an observer of Mars, using a large telescope under
conditions of good seeing, is in much the same position as someone
looking at the Moon with the naked eye or, at the best, with a pair of
weak opera glasses.

Though we have telescopes that could bring Mars to within one-tenth of
the

Moon's distance, it is impracticable to use such magnifications,
because our atmosphere is not steady enough.  As was pointed out
previously, simply increasing the power of a telescope very soon ceases
to show any finer detail and in fact soon shows less: it is like
looking at the reproduction of a photograph in a newspaper through a
magnifying glass the greater power only reveals the "graininess" of the
image.  To aggravate matters, as the orbit of Mars is notably
eccentric, really close approaches of the planet occur at rather rare
intervals, the best approaches of all being fifteen or seventeen years
apart (1971, 1988).

Let us first consider the undisputed facts about our little neighbor.
It is just over half the size of the Earth (4,200 miles in diameter),
and thus its surface area is 25 per cent of Earth's.  But
three-quarters of our world is covered with water, and since there are
no oceans on Mars, it follows that its land area is just about equal to
Earth's.

The Martian day is very nearly the same length as the terrestrial one,
being only half an hour longer, and the axial tilt of the planet is
also almost the same as Earth's.

t The Russian space probe that landed on Venus on October 18, 1967,
reported a temperature of 536* F. at ground level and an atmospheric
pressure at that point 15 to 22 times that at sea level on the Earth.
These findings were supported by the U.S. Mariner 5 fly-by on the
following day.

Mars therefore has seasons just as our planet has, but since the year
lasts 687 days, they are nearly twice as long.  The changing seasons,
as we shall see later, produce important effects which can be observed
even across the millions of miles of space that separate us from the
planet.

In the telescope Mars shows three main types of surface marking.  Most
prominent are the brilliant polar caps, which wax and wane alternately
in the two hemispheres, almost disappearing in summer and coming
halfway down to the equator in winter.  Not so bright, but still very
prominent, are the red or orange areas which cover most of the planet.
Finally, there are the irregular, dark regions that form a belt around
Mars, roughly parallel to the equator (Plate 58).

These are the permanent markings.  In addition, temporary clouds and
haziness can sometimes be observed, proving that the planet has an
extensive atmosphere.

The behavior of the polar caps immediately suggests that they are
composed of ice, and this explanation is now universally accepted.  The
Martian ice caps, however, must be far thinner than the enormously
thick and permanent crusts that lie at our poles.  This is obvious from
the fact that even the mild summers of Mars are warm enough to make
them shrink so much that on occasion the southern cap vanishes
completely.  They may therefore be only a few inches thick, the
equivalent of a very light fall of snow.

The orange regions, which give the planet its characteristic color,
show no seasonal changes and are generally considered to be deserts.
This word need not, however, conjure up a picture of a drab,
sand-covered waste.  According to some astronomers, the Martian deserts
show extremely brilliant coloring-brick-red and ocher being among the
terms used to describe them.

If this is true, they may resemble some of the incredibly spectacular
and garish deserts of Arizona.  However, it is now generally believed
that the brighter colors reported may be due to telescopic or visual
defects; they may, literally, be in the eyes of the beholders, not on
Mars itself.  But there is no doubt about the planet's general redness,
and it has been suggested that this is due to the presence of metallic
oxides, particularly iron oxide.  If this is the case, Mars is a world
which has, literally, rusted away.

The Martian deserts are probably fairly flat, for we should be able to
detect any high mountains by the irregularities they would cause on the
line between night and day.  There is, however, no reason why bills or
plateaus a mile or two in height should not exist, and indeed there is
some evidence for mountains near the South Pole.  The ice cap
occasionally splits into two sections as it shrinks, leaving an
isolated white patch which is always at the same location, as might be
expected to happen if there were high ground there.

Undoubtedly the most interesting areas of Mars are the dark regions,
which show seasonal changes linked with the melting of the polar caps.
The early observers made the fairly natural assumption that these
regions were seas and christened them "Maria."  The history of lunar
nomenclature was thus repeated, and though we now know that Mars is as
bereft of seas as is the

Moon, the names are still used, Mare Cimmerium, Mare Serpentis, and
Mare

Sirenium being among the more fanciful inventions.

With the melting of the polar caps in the spring and early summer, a
belt of darkness spreads slowly down toward the equator across the
"seas."  This change is so obviously produced by the release of water
from the caps that the evidence for the growth of vegetation is
impressive.  (It is, of course, conceivable that the change might be
due to chemical reactions among mineral deposits of some kind, but
there seems little point in advancing this complicated explanation in
place of the obvious and simpler one).  The color changes that occur
are strikingly similar to those that we should witness if we observed
our own Earth from space.  During most of the Martian year, the "Maria"
are blue-green or blue, but in the late winter and early spring they
become chocolate brown.

Before we jump to any conclusions regarding life on Mars, we must
consider what is known about its atmosphere.  The facts revealed by the
spectroscope are rather disconcerting: there is no sign of oxygen, and
we have tests which could detect the presence of this gas even if it
were only one-thousandth as common as in our atmosphere.  Carbon
dioxide has been observed; it is about twice as abundant on Mars as on
Earth.  Water vapor has not been detected in the atmosphere, but
infrared bands due to ice have been observed in the polar caps.

The air pressure at the surface of Mars is very low, perhaps
one-hundredth of its sea-level value here.  We

Children 0/ The Suit 0 267 would have to ascend twenty miles to
encounter so low a pressure on Earth, and even if the Martian
atmosphere consisted entirely of pure oxygen, we could not survive on
it.  It is probable that the bulk of the atmosphere consists of inert
gases such as nitrogen or argon.

Although the pressure is so low, the Martian atmosphere is very deep;
the weak gravity (one-third of Earth's) means a much slower falling-off
of density with height than on Earth.  This is supported by the fact
that clouds have been observed as much as 20 miles above the surface of
Mars.

Despite the tenuous nature of the Martian atmosphere, it is
surprisingly hazy and normally blocks out the light toward the blue end
of the spectrum.

The reason for this is unknown; although one is tempted to explain it
by the presence of fine dust in the atmosphere, it is difficult to see
how so thin a gas could support much solid material.

This particular mystery is less important than the undoubted fact that
the

Martian atmosphere is very tenuous and contains no oxygen.  Perhaps
the

Martian plants, if any exist, can obtain the oxygen they need from the
soil rather than from the atmosphere.  It should be remembered that the
other basic raw materials for plant life are carbon dioxide, water, and
sunlight, all of which are present on Mars, though water must be
extremely scarce.  So conditions on the planet are not too unfavorable,
and it has been found that a great many terrestrial microorganisms can
thrive and even reproduce in a simulated Martian environment.

Nor is the temperature of Mars so low, despite its greater distance
from the Sun, that life would be severely handicapped.  At noon during
the summer, temperatures of 80 degrees Fahrenheit have been recorded by
the thermocouple, and the equatorial regions of the planet must be not
much colder, on the average, than the temperate zones of Earth.
However, the range of variation is much greater, the Martian nights and
winters being extremely cold.  Even on the equator, the night
temperature is120 degrees

Fahrenheit.

It is worth remarking that the seasonal variations would not be a great
hardship to animal or mobile forms of life.  Owing to the smallness of
the planet, the length of the year, and the absence of geographical
barriers, it would be quite easy to migrate from one hemisphere to
another with the changing seasons.  The average speed required would be
only 5 or 10 miles a day.  Presumably nonmobile forms of life would go
into hibernation during the winter, as do the plants of our
Antarctic.

The shortage of water is probably one of the greatest handicaps to
Martian life, and the yearly melting of the polar ice is clearly of
extreme importance.  It is possible that the water is carried away from
the poles in the form of vapor; the atmospheric pressure is too low for
it to exist in the liquid state.

This is, perhaps, the moment to say something about the much-discussed
"canals," the network of fine, narrow lines reported by Schiaparelli
and

Lowell toward the end of the last century.  Lowell was convinced that
the canals formed a vast irrigation system built by an intelligent race
to conserve its dwindling water supplies.  Few astronomers today accept
this interpretation, and most do not believe in the existence of the
canals at all.  Yet there can be little doubt that large numbers of
curious linear markings do exist on the planet.  Even if they do not
actually form unbroken lines, many of them seem to be arranged in a
rectilinear fashion; but this does not mean that they must be
artificial.  They could quite possibly be old riverbeds, canyons, or
similar formations, and it is probably safe to say that nowadays few,
if any, astronomers could be found who believe that there is the
slightest evidence for intelligent life on Mars.  If anyone finds this
discouraging, we might point out that the Martians could hardly have
detected intelligent life on Earth if their telescopes were no better
than ours

Mars has two tiny satellites, only 5 or 10 miles in diameter, Phobos,
the closer of the two, is so near the planet that it is invisible from
the polar regions, being hidden by the curvature of the globe.  As it
moves around Mars more quickly than Mars revolves on its axis, it rises
in the west and sets in the east.  Much of the time it must be eclipsed
by the shadow of the planet, and as it would be about a quarter the
apparent size of our Moon, it would provide only a small percentage of
its light.  Deimos, the outer satellite, is still less conspicuous and
may not even show a visible disk to an observer on the planet, seeming
perhaps merely a bright star.

This is perhaps debatable.  They might be able to see the lights of our
great cities shining on the dark.  side of the planet.

These tiny moons may well be the first extraterrestrial bodies, next to
our own satellite, on which human beings will ever land.  Since their
gravitational fields are negligible, it would take very little power
for a spaceship to make contact with them once it had entered an orbit
around

Mars.  The gravity of Deimos must be so low that a man could jump clear
away from it, reaching escape velocity with his unaided muscles.

The Mariner 4 fly-by of July, 1965, gave the first tantalizing glimpse
of another Mars, proving, to the general surprise, that the planet was
almost as cratered as the Moon.  Some of the craters showed
considerable erosion, though whether by rain, sandstorms, or some other
cause has yet to be determined.  On the photograph-the famous Number
11, showing a crater some 70 miles across-there appeared a barely
perceptible straight line which at once started up echoes of the canal
controversy.  Though it is probably a natural feature, perhaps like a
lunar canyon in Plate 56, it is remarkably straight and narrow for at
least 150 miles.

The Mariner photographs proved nothing, one way or the other, about the
existence of Martian life, nor could they have been expected to do so.
The smallest details they showed were at least two miles across;
photographs taken of the Earth from meteorological satellites with
similar resolution give no hint of life, still less of human
civilization.

Through the 1970's, more advanced types of robot spacecraft will be
launched toward Mars, and our knowledge of the planet will advance in
quantum jumps, though there will be much that we shall never know until
the first men walk upon its surface.  The planned Voyager spacecraft
will be the

Martian equivalent of the Lunas and Surveyors, though they will have a
far more difficult task, as the communications range is at least 150
times greater and the power requirements, owing to the operation of the
square law, accordingly increased more than 20,000-fold.  Clearly, the
rate of flow of information back from the Martian surface will be very
slow.

For this reason it is essential to devise robot instruments that can do
as much thinking as possible for themselves and radio back their
conclusions-not masses of raw, undigested data.  Among these, now being
developed, are ingenious life-detecting devices-essentially, microbe
traps

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NASA

that can look for the various biochemical reactions that characterize
life as we know it on Earth.

Of the three possible outcomes of this search, they will be able to
report back only two, "Yes" or "Don't Know."  We may find Martian life
immediately, but to prove that it does not exist may take a hundred
years.  And to prove that it never did exist may take very much
longer.

After Mars and Venus have been reached (or at least orbited), the next
goal will be Mercury, nearest of all planets to the Sun.  It is a
small, airless world, not very much larger than the Moon, and perhaps
physically similar to it.  Until quite recently it was believed that it
kept one face always turned toward the Sun, so a whole astronomical
(not to mention science-fictional) mythology was built up of a world
divided between eternal day and eternal night.  If this were true-and
the smudgy maps made by visual observers for almost a century confirmed
it-then the same planet held both the hottest and the coldest places in
the Solar System.  The center of the daylight side, forever directly
beneath a sun twice as large (and therefore four times as hot) as
Earth's, would be at a temperature of at least 800 degrees, so that
such metals as lead or tin would be molten.

On the night side, shielded from any source of heat and with no blanket
of atmosphere to protect it, the temperature would be about450
degrees

Fahrenheit, or not far above absolute zero.

This description will be found in all astronomy books published before
1965; in that year it was discovered that the one fact we were certain
of about Mercury was untrue.  Radar echoes from the planet showed that,
after all, its "day" was not synchronized with its brief year (88 Earth
days); instead, it rotates on its axis once in 59 days.

This 59 does not seem to be a random number; it is exactly two-thirds
of the Mercurian year.  Some kind of resonance or tuning effect appears
to have been operating; though the tidal drag of the Sun has not locked
Mercury completely into step, it has at least partly succeeded in doing
so.

The orbit of Mercury is quite eccentric, the planet's distance from the
Sun varying between 28,500,000 and 43,350,000 miles.  As a result, its
orbital speed also changes considerably during the course of its 88-day
year, and this, combined with its slow rotation, can produce some most
extraordinary effects.  The interval between sunrises averages about
170 days, but Mercury is the only planet where the sun can rise, hover
uncertainly on the horizon for a few days, change its mind, set again,
and then

Plate 60.  Mariner 4'a photograph Number 11 of Mars.

NASA

reappear and creep slowly across the sky, perhaps repeating its
performance at sunset.  In the excessively unlikely event that there
are intelligent beings on Mercury, their knowledge of astronomy would
be either nonexistent or highly advanced.  It took the human race
several thousand years to unravel the movements of the heavenly bodies
on a much better-regulated planet.

These new discoveries do not change our picture of Mercury as a barren,
inhospitable planet with very great temperature extremes. Nevertheless,
it seems likely that it will be much easier to explore than Venus, and
it may serve as an excellent site for a solar research station.

Mercury will be a very interesting place to visit, but it seems
unlikely that anyone will really want to live there.

THE OUTER GIANTS

Beyond Mars the scale of the Solar System widens rapidly.  Between Mars
and

Jupiter there is what seemed, for a long time, to be a
disproportionately great gulf, as if a planet had been overlooked.

At the end of the eighteenth century an attempt was made to locate this
missing world.  The result of the search was unexpected; not one planet
was found, but hundreds, and we are still nowhere near the end of them.
The total number of asteroids, of all sizes, must run into at least
five figures.  Until recently astronomers were unable to keep track of
even the two thousand or so already detected; the work involved in
calculating their orbits was too great.  With the modern development of
electronic computers, this difficulty has been overcome, and almanacs
for minor planets can be calculated and printed quite automatically.
With this tedious work taken off their hands, astronomers no longer
regard the asteroids with quite such a jaundiced eye.

Even the largest of these little worlds, Ceres (480 miles in diameter),
is far too small to possess an atmosphere-its gravitational field is so
weak that any gas would escape into space immediately.  Nothing
whatsoever is known about their physical composition or surface
features, since the vast majority appear simply as dimensionless points
of light in the telescope.  The smaller asteroids are probably not even
spherical, but are simply jagged lumps of rock, mountains wandering
through space.  Although so many thousands of them exist, they cannot
constitute a "menace to navigation," as has sometimes been suggested.
The gulf between Mars and Jupiter is too enormous for a few thousand,
or even a few million, asteroids to go very far toward filling it.

Unfortunately one cannot, as some naY ve enthusiasts have suggested,
use these bodies to get a free ride around the Solar System.  In the
first place, suitable approaches would occur only at intervals of
decades or even centuries, and for one way only.  But much more
important, "riding on an asteroid" would confer no benefit at all.  The
spaceship would have to make a rendezvous with the body, and once it
had matched velocities, it would continue to travel along the
asteroid's orbit, whether the asteroid was there or not.  The presence
of a few million tons of rock would merely result in a little
propellant being wasted, to overcome its minute gravitational
attraction.  Of course, asteroids will be visited in their own right as
interesting (and perhaps exploitable) objects; they may one day
represent a very valuable source of metals and minerals for deep-space
operations.  But they are not of the slightest use to hitchhikers.

It is convenient to treat the four giant planets, Jupiter, Saturn,
Uranus, and Neptune, together, for they differ in degree rather than in
kind.  All have these points in common: they have a very low density;
have atmospheres composed of the light gases hydrogen, helium, methane,
and ammonia; and turn very rapidly on their axes.  Jupiter, being the
nearest and also the largest, is the most easily observed of the four;
much of the information gained about it probably applies to Saturn,
Uranus, and Neptune.

We can see no permanent surface markings on these planets; what we
observe is the top of an immensely deep and turbulent atmosphere,
perhaps thousands of miles thick.  They may indeed possess no stable
surfaces; the compressed gases may go on getting denser and denser
until the center of the planet is reached, with no definite transition
from gas to liquid, or liquid to solid.

Because they are so far from the Sun, one would naturally expect these
planets to be extremely cold, and indeed thermocouple measurements give
values of190 degrees F. for Jupiter and270 degrees F. for Saturn.  But
these values, it must be remembered, apply only to the top of the
visible cloud layer; conditions far below will be very different.

Even in a small telescope Jupiter is a fascinating and beautiful sight,
with its bands of cloud and the four bright sparks of its larger moons
changing their positions every night.  But we now know that there is
much more happening on and around Jupiter than meets the eye, for in
1955 intense radio emissions were discovered coming from the planet.
This was a great surprise; no one had expected such a large, cold body
to be a generator of radio waves.  One might have imagined this to be
true of the incandescent Sun, as has turned out to be the case, but on
occasion Jupiter is an even more powerful source of radio noise than
the Sun itself.

Most of these hissings: and fryings and cracklings come from a region
outside the planet, high above its equator.  This was the first
indication that Jupiter, like Earth, is surrounded by radiation belts;
in Jupiter's case they appear to be of great intensity, and they may be
a major hazard to astronauts.  In addition, there are occasional radio
outbursts-lasting for a few seconds up to more than an hour-which are
at much longer wavelengths (in the 10-meter band) and which are of
incredible power.  They sound very much like thunderstorm "static" and
appear to originate in the

Jovian atmosphere; there is also some evidence that they are linked
with definite regions of the planet's bidden surface.  If these radio
emissions are indeed due to thunderstorms, they must be of a violence
that we cannot begin to imagine.  A single second of Jovian
10-meter-band noise contains the power of a hundred billion terrestrial
lightning strokes.

Jupiter has twelve known satellites, more than any other planet.  One
of them (Jupiter V, so-called because it was the fifth moon to be
discovered) is a close approximation to a natural synchronous
satellite.  It takes 12 hours to revolve around Jupiter, and as the
planet rotates in 10, Jupiter

V takes six Jovian "days" to drift slowly around the sky.

Beyond Jupiter V, which is only about 75 miles in diameter, are the
four much larger satellites discovered by Galileo in 1609.  They are
all about as large as Earth's Moon, ranging in diameter from 2,000 to
3,000 miles.

Although the four large satellites all lie within little more than a
million miles of Jupiter, travel between them requires almost as much
energy as a journey from Earth to Mars or Venus.  This, of course, is a
consequence of Jupiter's extremely powerful gravitational field (Figure
20).

The remaining satellites are at much greater distance from the
planet-out to 14 million miles-and move On eccentric and highly
inclined orbits.  They are all less than 100 miles in diameter, and the
outermost ones may well be asteroids that Jupiter has, perhaps
temporarily, captured as they strayed.  into its neighborhood.

Far beyond Jupiter-indeed, at almost twice its distance from the
Sun-the slightly smaller but much lighter planet Saturn moves on its
leisurely, 29-year orbit.  With ten moons, and the same type of
hydrogen-helium-methane ammonia atmosphere, Saturn would probably be
regarded as a not very exciting carbon copy of Jupiter were it not for
one astonishing feature-its unique system 4 rings.  Through the
telescope, they look so obviously artificial that it is hard to believe
that they do not form part of some intricate and beautiful machine.

The rings, which span a total diameter of 170,000 miles, consist of
myriads of particles traveling around the planet in almost perfectly
circular orbits.  They also lie in a plane so flat and thin that when,
as happens every fifteen years (1966, 1981), the rings are edge-on,
they appear to vanish completely.  Although they appear solid, when a
star passes behind them it can still be seen shining; at close
quarters, the rings would probably look like a sheet of hail or snow,
perhaps only a few yards in thickness-a kind of eternal blizzard,
forever sweeping around Saturn.

Atbough ten moons of Saturn have been discovered, there can be little
doubt that others still remain undetected.  The latest to be found,
Janus, practically rolls along the very edge of the rings, and was
spotted during their disappearance in 1966.  All have been dignified
with names, not merely, as in Jupiter's case, with numbers.  The muster
is so poetic that I cannot resist giving it in full, working outward
from the planet, it runs

Janus, Mimas, Enceladus, Tethys, Dione, Rhea, Titan, Hyperion, Iapetus,
and

Phoebe.

Most of these little worlds are only a few hundred miles across, but
the largest, appropriately named Titan, is a giant among satellites.
Being 3,500 miles in diameter, it is larger than Mercury and not much
smaller than Mars.  As a result of its size, it has sufficient gravity
to retain an atmosphere, a thin, cold envelope of methane.  As this
could be a good propellant for nuclear rockets (see Chapter 24), Titan
may play a vital role in the opening up of the outer planets.  It may
provide us with a refueling point, halfway to

Pluto.

There appears to be something rather odd about the smaller of these
moons, for their densities are abnormally low-in at least two cases,
less than that of water.  Although this is also true of Saturn, its
deep atmosphere easily accounts for its low density, but worlds only
three or four hundred miles in diameter cannot possibly have an
atmosphere.  Perhaps, as Fred

Hoyle has suggested, they are extremely porous, "gigantic snowballs."

The strangest of all the satellites, however, is the ninth from the
planet-Iapetus, 700 miles in diameter.  On one side of its orbit
Iapetus is at least five times brighter than on the other.  This means
that it is either a very peculiar shape or that it has some surface
feature of exceptional brilliance on one hemisphere.  Iapetus is only
one of the intriguing bits of unfinished, indeed, barely started,
business represented by Saturn-its glorious icy halo and its
16-million-mile-wide family of moons.

We know very little about Uranus and Neptune because their immense
distances make it impossible to observe them successfully except in the
very largest telescopes.  Once again, they are giants with tremendously
deep hydrogen-methane atmospheres, but possibly because of their
extreme coldness they do not show the disturbances that can be seen on
Jupiter and, to a lesser extent, on Saturn.

Uranus has five satellites-Ariel, Umbriel, Titania, Oberon, and
Miranda.  (Presumably the next to be detected is doomed to be
christened Caliban.)

Titania is about half the size of our Moon, but the others are much
smaller.  Neptune has only two moons-Nereid and Triton; the latter is
one of the largest known satellites, about 3,000 miles in diameter.

Until 1930 Neptune's orbit marked the frontier of the Solar System.  In
that year Pluto was discovered, as a result of a long search by the
Lowell

Observatory.  The discovery was based on mathematical calculations by
Dr.

Lowell, but it has now been found that Pluto cannot be the planet whose
existence he predicted.  It is far too small, having a diameter of less
than 4,000 miles, so we can only assume that its discovery was
fortuitous and that the planet for which Lowell was looking still
remains to be found.

Although nothing is known about Pluto except its size and its orbit, it
probably resembles the inner planets in composition and so will have
nothing in common with its giant neighbors.  It must be exceedingly
cold, the temperature never rising above350 degrees F. Almost all gases
except hydrogen and helium would be liquefied at this temperature, so
it is not likely that Pluto has an atmosphere.  It has an unusually
long "day" for an outer planet-6.4 days.  This fact, and its peculiar
orbit, has led some astronomers to suggest that it may be a "lost"
satellite of

Neptune.

Planets, satellites, asteroids, comets-this completes our survey of
the

Solar System.  In Chapter 26 we will discuss the probable existence of
other planetary systems around other stars, but as far as our present
definite knowledge goes, the only possible abodes of life in the
universe are the worlds we have been describing.  Most people will
probably feel that the resulting picture is not exactly an encouraging
one.  They may be right; there may well be no advanced form of life in
our Solar System beyond the atmosphere of the Earth, and no life of any
kind except a few lichens on the Moon and Mars.  Yet there is a danger
that this assumption, plausible though it may seem, is based on a
hopelessly anthropomorphic viewpoint.  We consider that our planet is
"normal" simply because we are used to it, and judge all other worlds
accordingly.  Yet it is we who are the freaks, living as we do in the
narrow zone around the Sun where it is not too hot for water to boil
and not too cold for it to be permanently frozen.  The 11 normal"
worlds, if one takes the detached viewpoint of statistics, are the

Jupiter-type planets with their methane and ammonia atmospheres.

We do not know the limits to the adaptability of life.  On our planet
life has learned to function over a temperature range of almost 200
degrees

Fahrenheit.  It is based on oxygen, carbon, and water, which are among
the most abundant substances in the crust of the planet.  Yet these
basic materials are utilized in very varied fashions.  Some organisms
(e.g., jellyfish) consist almost wholly of water; others, such as
cacti, use very little and survive in environments too dry for any
other form of life.

Certain bacteria have even performed the astonishing feat of partly
replacing carbon by sulfur and can live happily in boiling sulfuric
acid.

The importance of water arises from the fact that it dissolves such an
enormous variety of substances, and so acts as a medium in which
countless chemical reactions can take place.  In this respect, however,
it has a number of rivals, liquid ammonia among them.  On a planet
whose temperature was less than28 degrees F. but above108 degrees F."
ammonia might take the place of water for many purposes.  On even
colder worlds methane, which remains liquid down to the extraordinarily
low temperature of -300 degrees F."  might take over.  It is true that
most chemical reactions proceed very slowly, if at all, at low
temperatures.  However, fluorine, the most reactive of all elements,
could conceivably replace oxygen under these conditions.

In the direction of increasing temperatures, it is again difficult to
set a limit to nature's ingenuity.  The discovery of silicon-carbon
compounds has opened up new vistas in organic chemistry, and a life
form based partly on silicon is by no means beyond the bounds of
possibility.  The silicon compounds retain their identity at
temperatures high enough to destroy their carbon analogues, and they
might make life possible on worlds a few hundred degrees hotter than
Earth-for example, on parts of Mercury.

Faced with an unpromising environ men life has the choice of two
alternatives-adaptation or insulation.  Examples of both can be seen on
our world.  In the polar regions the seals and penguins adapt; the
Eskimos insulate.  One of the most remarkable examples of the latter
technique is provided by the humble water spider, a wholly air
breathing insect which nevertheless spends much of its time submerged. 
By carrying its appropriate living conditions with it, it manages to
survive in a completely alien environment.  In the same manner, carbon
life based upon water could conceivably exist even on the frozen outer
worlds.  One can imagine beings with tough, insulating skins through
which the heat loss would be very small.  As long as they had some
source of energy-chemical, solar, perhaps even nuclear-and the
necessary food, they could still survive though their surroundings were
not far above absolute zero.

It may be objected that though such life forms might be able to exist
on very cold worlds, they could hardly have originated there.  The
indigenous life would probably be based on low-temperature reactions
and would not be much hotter than the surroundings.  Yet from this type
of organism higher forms of life might be able to evolve, just as the
warm-blooded mammals evolved from the coldblooded reptiles.

We know, of course, very little about the laws that govern the
appearance and the evolution of life on any planet.  The above
speculations may help to show the danger of generalizing from the
solitary example of our own Earth and trying to produce laws applicable
to totally alien planets.  It is illogical to conclude that because the
other worlds of the Sun are so different from our own, we cannot hope
to find familiar forms of life there.

It is the very strangeness of the planets that provides one of the
greatest incentives for visiting them.  If they were all like Earth, we
might just as well stay at home.

THE COMMERCE OF THE HEAVENS

For I dipt into the Future, far as human eye could see Saw the Vision
of the world, and all the wonder that would be; Saw the heavens fill
with commerce, argosies of magic sails, Pilots of the purple twilight,
dropping down with costly bales.

When Alfred, Lord Tennyson, wrote those words more than a century ago,
he was certainly not looking beyond the atmosphere, and his vision must
have seemed the wildest fantasy to his readers.  But now it is the
everyday reality of our age, and perhaps the real wonder, which would
have astonished

Tennyson most of all, is that our pilots are not only dropping down
with costly bales; they are dropping down with cheap ones.

This is the pattern that must be repeated in space if the exploration
of the planets is to be more than a long-term scientific project that
only a prosperous world state can afford.  Even on this basis it would
certainly be possible and worthwhile; but all the lessons of the past
and everything we can foresee in the way of technological progress
suggest that this is taking a very pessimistic and shortsighted view.

The pace and ultimate extent of what we may call the exploitation of
the

Solar System depends upon two factors.  The first is a vast unknown,
though there are small patches where our ignorance is slowly
lightening.  It involves the resources and surface conditions of the
planets and the technologies that may be devised to use, control, or
combat them.  The second is even less predictable, the motivation of
future societies. We have already seen, in the early history of the
Space Age, how politics and technology react upon each other, in both
directions, and it would be naive to assume that this process will not
continue.

We will discuss these now unanswerable, but not unarguable, questions
in later chapters.  Their ultimate importance, however, depends upon
something that can be defined a little more precisely, even at this
early stage-the cost of space flight.  If travel to the other planets
can be made little more expensive than today's intercontinental jet
transportation or an around-the-world ocean voyage, the heavens will
indeed fill with commerce.

But if the cost is a thousand fold higher, all we can look forward to
is the occasional scientific expedition.

This would certainly be the case if we were always restricted to
chemical propellants, such as the kerosene oxygen and bydrogen-oxygen
combinations which power most of today's large rockets.  Even here,
however, there is great room for improvement-certainly by a factor of
ten, perhaps by one of a hundred when all possible techniques have been
developed.  That might not be sufficient for true commercial space
operations, but it would allow for a good deal of planetary travel
without bankrupting the human race.

The most powerful chemical propellant combination used today-the
liquid-bydrogen, liquid-oxygen mixture burned in the two upper stages
of the Saturn 5-gives an exhaust speed (in vacuum) of about 10,000 mph,
or more than half the velocity needed to go into orbit around the
Earth.  There are a few theoretically more powerful combinations; for
example, oxygen can be replaced by the still more reactive element flo
urine producing an improvement of about 5 per cent.  Another 5 or 10
per cent can be obtained by adding light metals such as beryllium or
lithium, but the most we can hope for is an advance of 10 to 15 per
cent over present values, and this at great difficulty and expense.

It is just possible that the chemists may produce weird, meta-stable
substances, not occurring in nature, which can provide more energy than
existing propellants, but it would be foolish to count on it.  There
are more promising lines of development.

One already mentioned in Chapter 19, is the reusable booster or
aerospace plane, which flies or parachutes back to its base, to be
refueled and used again.  Such a vehicle becomes even more attractive
if it can use the surrounding atmosphere for propulsion during its
ascent.  Although the rocket has the freedom of space, because it
carries its own oxygen, it has won this freedom at an enormous cost in
extra weight and size.  One can imagine a system in which, for the
first stage at least, only the liquid hydrogen was carried aboard the
vehicle and the oxygen was obtained from the surrounding air.  Such a
reusable space transporter might take off and land like a conventional
aircraft, carrying on its back the pure-rocket stage which made the
final leap into orbit.  There can be no doubt that same thing like this
has to be developed; we cannot continue indefinitely to carpet the
Atlantic seabed with Saturn 5's.

Refueling in space, at orbital filling stations kept supplied by
tankers from Earth, may play an important role in interplanetary
operations.  But it does not necessarily result in great savings; in
fact, it increases the total amount of propellant required for a
mission.  The great advantage of orbital refueling is that it allows
the use of much smaller spacecraft, though they have to carry out many
more flights than a single giant vehicle.

It becomes much more attractive and may result in major savings if the
propellants can be obtained from low-gravity sources such as the Moon,
as suggested in Chapter 19.  And refueling, on the Moon or on bodies
with known sources of hydrogen such as Titan, could also result in
great economies.

When all these things are added up, one can imagine a day when a
twenty-first-century millionaire (should any still exist) might be able
to afford a ticket to Mars.  For commercial operations, we must do a
good deal better than this.

It is important to realize that the difficulty of space travel does not
lie in the great amount of energy needed.  As was pointed out in
Chapter 19, to lift one man away from the Earth requires only 1,000
kilowatt-hours of energy, costing only about $10.  It is indeed
tantalizing to realize that if we could build an elevator to the Moon,
it would cost $10 a passenger to get the rel

It costs billions today because our portable energy

Liquid hydrogen

Propellant pump

Fig.  25.  Solid-core nuclear rocket.

sources are too heavy.  Ninety-nine per cent of the fuel in a big
rocket is expended in merely lifting other fuel; the remaining one per
cent could do all the work that is really required.  If we had a
virtually weightless energy source, the problem would be solved.

We have such a source, at least in theory.  Nuclear reactions release
about a million times as much energy, weight for weight, as chemical
reactions.

The 2,350 tons of propellant in a Saturn 5 could be replaced by a few
pounds of fissionable material if energy were the only criterion.

Unfortunately, it is not as simple as this.  Pure energy can provide
heat or radiation, but it cannot provide thrust unless it has something
to react against.  So even with nuclear power, we are still forced to
use the rocket principle.  An exhaust jet of some material-a "working
fluid"-has to be expelled; the only difference is that its energy of
motion will now be derived from nuclear, and not from chemical,
reactions.

Although the basic principles of the "atomic rocket" were published
within a few years of the first release of nuclear power, the
development of practical, flyable units has been an extremely difficult
and lengthy task, covering two decades of time and costing hundreds of
millions of dollars.

On paper, all that one has to do to build an atomic rocket is to
construct a high-temperature reactor and blow hydrogen through it
(Figure 25).  The heated gas can then be allowed to expand through a
nozzle, to give a propulsive jet.  However, unless temperatures of
4,000-5,000 degrees F. can be attained, nuclear rockets have no
advantage over chemical ones-and many grave disadvantages, such as the
need for heavy radiation shielding.

Despite these problems, nuclear rockets have Dow been successfully
built and tested in the United States as part of the Atomic Energy
Commission's

Project Rover.  Exbaust velocities about double those of chemical
rockets have been achieved at quite high thrust levels-more than a
hundred tons-together with remarkably long running times.  Although
nuclear engines are not likely to be used for takeoff from Earth, they
will prove very valuable for the final stages of deep-space craft,
doubling or tripling their payloads.

But this improvement, worthwhile though it is, uses only a minute
fraction of the energy available from nuclear sources.  This is already
so enormous that it makes the demands of even the most ambitious
interplanetary expeditions look quite trivial.  A 25-megaton H-bomb
(like the one lost by the United States Air Force off the coast of
Spain in 1966) liberates enough energy to carry 2 million tons to Mars.
This astonishing statistic shows that we already have enough sheer
power to do anything we wish in the

Solar System; unfortunately, we are not yet clever enough to control
it.

Some most ingenious (and occasionally hair-raising) schemes have been
suggested for very high-performance nuclear-propulsion systems.  In
some, the fissionable mate rial (U".."  or plutonium) would be in the
gaseous state, and-so the temperature limitations of today's atomic
rockets would be removed.  If the slightly fantastic engineering
problems involved in building "gaseous-fission reactors" can be solved,
the economics of space flight would be totally transformed.  The whole
of the Solar System would be thrown open to mankind.

Maxwell Hunter, general manager of research and development for the

Lockheed Missile and Space Company, has outlined a hypothetical
gaseous-fission ship in his stimulating book Thrust into Space.* It
sounds far too good to be true, and perhaps it is, but it is based
entirely on theoretically sound engineering principles.  Hunter's
spaceship would weigh 500 tons, of which no less than 100 would be
payload.  And its propellant fluid would be ordinary water, with all
that this implies for ease of storage and refueling, not to mention
cost.  Perhaps even more remarkable, after one has grown used to the
multistage rockets of today, the propellant tank is only a small part
of the total volume.  As Max Hunter writes, "The design looks more like
a Buck Rogers spaceship than a conventional ballistic missile-the cargo
compartment takes up more space than the propellant tank.  That is the
way a good spaceship should be."

Running on a weekly schedule, such a ship could carry 5,000 tons of
payload to the Moon every year, and ten of them could provide the
tonnage of supplies now delivered to the United States bases in the
Antarctic.  It could even compete commercially with existing jet
transports, delivering cargo more-ebeaply between any two points on
Earthin less than an hour.

Once again, it should be stressed that such a spacecraft is very much
in the realm of theory and that its construction involves enormously
difficult engineering problems.  It may take the remainder of this
century before we know if they can be solved.

Yet beyond the fission-powered (uranium or plutonium) systems is an
even more glamorous possibility, the use of fusion (i.e."  hydrogen)
power.  So far, this has been liberated only explosively, and vast
efforts have been made to achieve sustained fusion, or thermonuclear,
reactions.  The task has proved more difficult than earlier optimistic
fore

Holt, Rinehart and Winston, 1965.

casts suggested, but few doubt its ultimate realization.  When that
comes about, we shall have all the power we need to do anything on
Earth, in space, or on the planets.  And we shall be able to think
seriously about going to the stars (Chapter 29).

To come back from this intoxicating dream world to the more immediate
future, nuclear energy may also be used to provide thrust by electrical
rather than thermal processes.  Various types of electric rockets have
already been tested, some on actual space flights.  They operate by
accelerating charged particles or ionized gases in electric fields.

Extremely high jet velocities can be achieved in this way, but the
thrust levels are microscopic-mere fractions of a pound.  Obviously,
such devices are useless for the escape from Earth, but once in orbit
they could continue to provide acceleration for days or weeks, until
very high speeds were finally achieved.  So the nuclear-energized,
electrical-propulsion systems may be developed for use in deep space,
while chemical rockets are still used for takeoff and landing.

Mention should also be made of Project Orion, the most startling of all
the ideas put forward for space propulsion by nuclear energy.  This
involves nothing less than a series of atom-bomb explosions-one every
few seconds-which would kick a spaceship into orbit.  The ship would
carry a large number of small bombs (perhaps a thousand), and these
would be detonated a short distance from a massive pusher plate, which
would take up the shock.  The impact would be smoothed out through
powerful springs, so that the spacecraft received a fairly uniform
acceleration.

Design studies and a few tests with conventional explosives showed that
this nuclear-pulse technique would certainly work, but it would become
economical only for very large spacecraft carrying payloads of
thousands of tons, and it will be quite a few years before there is a
pressing need for these.  Meanwhile, of course, the nuclear-test ban
has put a stop to further development along these lines-permanently,
many will hope.  A-bombs going off at the rate of one a second for
twenty minutes at a time just outside the atmosphere may be too high a
price to pay for the conquest of the Solar

System.

Finally, it is necessary to ask the question: Is the rocket the only
way of crossing space?  May we not one day discover better forms of
propulsion, for example, the

11 space drives" and "antigravity" devices beloved of the
science-fiction writers?

Perhaps; but at the moment there is not the faintest sign of such a
breaktbough.  The reaction principle throwing mass in one direction to
obtain a thrust in the other-still remains the only means of driving a
space vehicle.  Not even in theory is any alternative known.

It can be shown that all the mechanical devices that have been proposed
from time to time (see Chapter 1) are based on ignorance of simple
dynamics.  In the final analysis, which may be so difficult for a
complicated gadget that no engineer would waste his time attempting it,
they are all schemes for lifting oneself by one's own bootstraps.

It is not so obvious that gravity screens of the type used by Wells in
The

First Men in the Moon, and by countless other writers, also involve a
fundamental fallacy.  If such a substance as Wells's "Cavorite"
existed, which cut off gravity as a roller blind cuts off the sunlight,
it could be used to produce an unlimited amount of energy-from nowhere.
It would be necessary only to put the screen under a heavy object, let
it soar upward, remove the screen, and collect free energy from the
falling body by a rope-and-pulley system.  The cycle could be repeated
indefinitely, giving a classic perpetual-motion machine.

But the energy to lift an object out of the Earth's gravitational field
has to come from somewhere; it is equivalent, remember, to an ascent of
no less than 4,000 miles against a force equal to gravity at sea level.
So an antigravity system, even if it is possible, may not be as useful
as it might seem.  It will require an enormous amount of energy to run
it; and if that has to come from electrical generators and conventional
fuel supplies, we might be better off using rockets, after all.

The late Roger Babson, statistician and business analyst, endowed a
"gravity research foundation" in the hope that one day we would be able
to do something about gravity.  Most scientists would agree that this
is a vain expectation.  Probably all would agree that if there is any
advance in this field, it will result from.  discoveries in a totally
different area of science.  Perhaps when we can experiment with matter
and energy under the weightless (though not gravityless, remember)
conditions in an orbital laboratory, there may be some hope of
progress.  If antigravity is ever found, it will be by someone who
isn't looking for it.

Surprisingly enough, there is one way in which a form of gravity
propulsion can be used to considerable advantage in space flight.  A
rocket falling into the gravity field of a planet from a great
distance-say, a million miles-gains speed on the approach; then, if it
merely loops around the planet without making contact, it loses all
this speed on the outward climb.  When it is once more a million miles
away, it is moving at exactly the same speed with respect to the planet
as before, having neither lost nor gained even a fraction of a mile an
hour.

However, it will be moving in a completely different direction; it may
well have been deflected by ninety degrees or more by the encounter. It
is

Drecisely as if it has bounded off the planet, like a ball thrown
against a perfectly elastic wall.  In this case, too, there is no
change of speed, only of direction.

So how can anything be gained?  It cannot-if the wall is stationary.
But if the wall itself is moving, the ball will acquire some of its
velocity during the impact.  And this is what happens in the
astronomical case, for the planets are all moving in orbit around the
Sun.  After a spacecraft has "bounced" out of a planetary field, its
speed with respect to the planet will not have changed; but its speed
with respect to the Sun, which is the important factor, will have done
so, perhaps by a very large amount.  So it may have gained, or lost, a
considerable amount of energy.

In the over-all picture, of course, there is no change of energy.  What
the rocket gains, the planet loses, so that its velocity is reduced by
an infinitesimal amount.

By skillful navigation, therefore, and practically no expenditure of
rocket fuel, we can play a kind of "interplanetary billiards," perhaps
using the gravity fields of several planets in successioD-gaining or
losing speed at strategic points.  The operational advantages could be
enormous; for example, in 1978 it would be theoretically possible to
launch a rocket from Earth to the outer planets, Saturn, Uranus, and
Neptune, bouncing from one to the next.  The tour would take 9
years-though normally it would take 30 years to go merely to Neptune at
the same departure speed from Earth.

The Jupiter probe described in Chapter 21 would employ the same
principle.

This is an interesting example of the way in which we can take
advantage of the laws of nature; a more obvious and even more important
example is the use of atmospheric braking, though that can be employed
only to lose speed.  But this is just as vital as gaining speed; manned
space flight would be out of the question for decades to come if the
enormous velocities developed in the return to Earth or a landing on
Mars had to be neutralized entirely by retrorockets.

Naturally, scientists have looked for other cosmic energy sources that
may be exploited for space propulsion, and so far they have found only
one-the

Sun.  Solar panels, turning the Sun , s rays into electrical energy,
are of course used in almost all space probes as a source of power for
the electronic equipment and the radio transmitters.  But they could
also be utilized in place of nuclear reactors, to power low-thrust
electric-propulsion systems.  An alternative idea is to use the Sun's
rays directly to heat a gas (probably hydrogen) and to let it expand
through a nozzle.  The solar-powered rocket bears a somewhat uncanny
resemblance to the device which the ingenious Cyrano de Bergerac used
in his Voyage to the

Sun.  This was a large box surmounted by burning glasses so that "the
sun's rays uniting by way of the concave glasses would attract a
furious abundance of air to fill it, which would lift up my box, and in
proportion as I rose up the horrible wind which rushed through the hole
could not reach the roof except by passing furiously through the
machine and lifting it up The solar rocket would also use concave
reflectors and would be driven by a "horrible wind" of hot hydrogen.

Yet another -possibility, which seems even more fantastic but is
scientifically completely" sound, is to use sunlight itself for
propulsion.

Although nothing could appear more imponderable than a sunbeam, even
light has weight and can exert a definite pressure when it falls upon a
surface.

That pressure is, of course, almost unimaginably small; yet it has been
measured, and comes to about one-ten millionth of a pound on every
square foot of surface directly facing the Sun.  If the surface is a
good reflector, the force is, doubled.

So imagine a sail made of the thinnest possible plastic sheet, mirror
coated on one side by a layer of aluminum

Richard Aldington translation (New York: Orion Press, 1962).

only a few atoms thick.  Even if it were a mile on a side, it might
weigh less than ten tons; and the total pressure of sunlight acting on
it would come to about five pounds.  So it would slowly start to move,
"blown" by the

Sun at an acceleration of about one-four-thousandth of a gravity.

This rate of increase of speed may sound utterly negligible, but it is
maintained indefinitely in the vacuum of space.  After one day the sail
will have gained 500 mph, after ten days, 5,000 mph, which begins to
look interesting, especially since it costs nothing, because the "fuel"
is free.

If one could devise sufficiently lightweight rigging and methods of
controlling the angle of the sail, then small cargoes or robot space
probes might be towed around by this means.

At first sight it might appear that solar sailers could travel only
away from the Sun, since radiation pressure is like a wind blowing
forever outward from the center of the Solar System.  But just as a
conventional sailboat can tack against the wind, so a sun jammer could
move toward an inner planet.  By tilting its sail so that it lost part
of its orbital speed, it would necessarily fall in toward the Sun.

Whether solar sailboats are practical or not, they are certainly a
delightful idea.  Perhaps one day they may be developed for sporting
purposes, and "rounding the Sun" may have something of the glamour that
rounding the Horn did in the seafaring annals of the past.  If so,
another line of Tennyson's verse will come strikingly true: the heavens
will indeed see "argosies of magic sails."

TOMORROW'S WORLDS

That stay in Britain made me envisage a hypothetical empire governed
from the West, an Atlantic world.  Such imaginary perspectives have no
practical value; they cease, however, to be absurd as soon as the
calculator extends his computations sufficiently far into the future.

Memoirs of Hadrian, M. YOURCENAR

We will now take as proved the argument, developed in the last
chapters, that one day the large-scale transportation of men and
materials to the planets will be relatively cheap and simple.  If by
1966 a 5-ton hydrogen bomb could send 2 million tons to Mars, though
admittedly in rather small pieces, it is not particularly optimistic to
hope that by 2066 a few hundred tons of advanced nuclear engineering
would deliver several thousdnd tons of payload anywhere in the Solar
System.  Indeed, when one considers the past history of technology, any
other assumption appears totally unrealistic, a refusal to face high
order probabilities, if not indisputable facts.  So let us be realistic
and consider the colonization of the planets.

Much that has been said about exploring and exploiting the Moon in
Chapter 19 can be applied to similar airless bodies-MerCUry, the larger
asteroids, the satellites of the giant planets, perhaps even Pluto. All
these worlds, many of no mean size, are essentially in a space
environment.  Though their surface temperatures vary wildly-from at
least 1,000 degrees F. in the case of Mercury, to450 292

degrees F. for Pluto-these figures do not have anything like the
meaning they would in a terrestrial context.  In a vacuum it is
relatively easy to arrange almost complete protection against extremes
of heat or cold; the familiar thermos flask is proof of that.

On Mercury and the Moon, reflecting surfaces turned toward the slowly
moving Sun would take the heat load off buildings and equipment, and
the diverted energy could be usefully employed.  It is known that the
surface material of the Moon is an excellent thermal insulator, so that
the temperature is constant a few feet underground.  This is probably
true of all the other planets and satellites which have solid, stable
surfaces.

Even on very cold worlds the problem is more likely to be one of losing
beat at a controlled rate rather than conserving it.  Electrical
equipment, nuclear reactors, the explorers themselves, all generate
vast numbers of calories, which must be dissipated.  One could die of
heatstroke in a too-well-insulated base on Pluto, even though the
temperature a few inches away was not far above absolute zero.

The investigation of all these airless worlds will be greatly
simplified by a factor that it is very hard for us to appreciate,
because it is as unfamiliar as weightlessness.  They will have no
weather.  There will be wholly predictable climatic (for want of a
better word) variations due to their periods of rotation, but these
will affect only the temperature of the surface layers.  Storms, rain,
fog, cloud, wind, dew, snow-the innumerable meteorological phenomena
which control our lives, and often our deaths, on Earth will all be
absent.  At one sweep this will remove most of the hazards of
exploration.

But, of course, there will be others.  On some of the larger, cold
satellites there may possibly be lakes of liquefied gas, or "snow"
fields of frozen ammonia.  Temperature changes of only a few degrees
could have spectacular consequences in such places.  This may be
particularly true of some of Saturn's low-density moons; even
apparently dead and changeless worlds may produce some unpleasant
surprises and should be inspected carefully from space before a landing
is made.

After the Moon, it now appears fairly certain that Mars will be the
chief target for exploration, and a permanent base may be established
there before the end of the century.  In many ways it will be a less
difficult challenge, and perhaps a much more rewarding one.  No one
really expects to find life on the Moon; everyone hopes to find it on
Mars.

The presence of an atmosphere, tenuous though it may be, has a
considerable effect on Martian surface conditions.  It moderates the
temperature extremes (though they are bad enough) and is a better
shield against meteoroids than is the Earth's atmosphere.  With this
danger to surface structures eliminated, it would be possible to erect
large, pressurized domes, big enough to e6close whole settlements or
even small towns.

Air-supported flexible shelters, like grounded balloons, are already in
wide use for military and other applications.  They would be even 'more
practical on a world where gravity has only one-third of its
terrestrial value; on Mars, domes a thousand feet or more in diameter
could easily be constructed.  Inside,these great bubbles of air the
explorers, or colonists, would live in a shirt-sleeve environment; only
when they went outside would they have to wear pressure suits or travel
in closed vehicles.  If desired, the domes might be made of some
transparent, flexible plastic to let through the sunlight, though this
is by no means essential and might result in too great a beat loss
during the night.  The best arrangement would be a dome which was
transparent during the day (when the temperature can rise to the 80's),
so that it collected heat on the greenhouse principle, and which could
be made opaque at night

So as not to have too many eggs in one basket, it would be better to
use several small domes, interconnected by airlocks, instead of a
single large one; the major buildings could also be pressurized in an
emergency.  It should be realized that even if the dome were badly
ripped or punctured, it would take many minutes to collapse, and there
would be ample time for anyone out of doors to reach safety.

It will be very convenient if aircraft can be used on Mars, as they
would be invaluable for exploration and travel.  At the moment it is
not certain if this will be the case; the low gravity assists aircraft,
but the excessively thin atmosphere means that they will require very
large

-I have described such a colony in the novel The Sands of Mars (New
York:

Harcourt, Brace & World, Inc."  1967).

Tontorrotv's Worlds o 295

wings and high cruising speeds.  (Of course, self-contained -power
systems will also be necessary, because of the absence of oxygen.)
Perhaps we may see the revival of blimps on Mars, as we may see that of
railroads on the

Moon.

A few years ago it seemed that most of these ideas might also be
applicable to Venus; now the discovery of 1,000-pound-per-square-inch
surface pressures and furnace hot temperatures makes this planet one of
the Solar

System's less desirable building sites.  Any vehicle that can land on
Venus will have to be a combination of spaceship and submarine; unless
there is some extraordinary incentive, all our explorations will be
done by robots for a long time to come.  One may speculate about the
existence of very high mountains (which radar does indeed suggest),
where the temperature and pressure are both low enough to make manned
operations feasible.  Even if this turns out to be the case, it seems
unlikely that permanent bases will be established there in the
immediate future.

Yet, a century or two ahead, Venus represents opportunities which
surely will not be neglected.  It is inconceivable that a planet as
large as Earth, drenched with solar energy, and only a few
light-minutes away, will have nothing to offer our descendants, who
will have at their command forces and technologies that we can scarcely
imagine.  The Harvard astronomer Dr.  Carl

Sagan has suggested that, even if Venus has never been able to develop
life of its own, it might be seeded from Earth.  At some level in the
atmosphere, between the40 degree cloud top and the + 1,000-degree
surface, water may exist in the liquid state, and small aerial life
forms probably bacteria, which have an extraordinary adaptability-migbt
be able to flourish.  The biologists of the future may be able to
devise cultures which could break down the vast quantities of carbon
dioxide, release oxygen, and eventually change the whole climate of
Venus by reducing the present greenhouse effect which now makes the
surface so hostile.  Then, without any further intervention, a
biological chain reaction might be started; after all, something quite
similar once took place on Earth, to give it an atmosphere in which
oxygen-breathing creatures could exist.

This is certainly a grandiose idea, but it differs only in scale from
the projects that have brought life to the barren places of this
planet.  That we of the twentieth century can think of plausible ways
in which it might be achieved suggests that our descendants will know
far better ones.

The giant planets, Jupiter, Saturn, Uranus, and Neptune, present even
greater problems than Venus, yet at the same time they may present even
greater opportunities, though in a still more distant future.  Since we
know practically nothing about the outer three, except that they are
basically similar to Jupiter, we will take, that planet as
characteristic of all the "gas giants."  That is certainly-quite wrong
in detail, but our ignorance leaves us little alternative.

The overwhelming fact about Jupiter is its sheer size; it contains more
material than all the other planets added together.  (Dr.  Isaac Asimov
once remarked that the Solar System consists of Jupiter plus debris.)
Even if it possessed a solid and readily accessible surface, the task
of exploring a planet with 120 times the area-350 times the land
area-of Earth would be awe-inspiring.

In fact, it is possible that Jupiter has no stable, solid surface.  Its
hydrogen-methane-ammonia atmosphere may grow steadily denser with
increasing depth, until, at some enormous pressure, it turns liquid and
then finally solid.  However, the existence of such a semipermanent
feature as the Great Red Spot, which has now been under observation for
three centuries, suggests that there must be some degree of stability
beneath the whirling cloud belts which are all that we can see from our
distant viewpoint.

What makes Jupiter of such extraordinary interest, despite the
difficulties of approaching it, is the fact that it may be a primitive
world, a proto planet or even a proto sun  It may show us how our own
Earth came into being, and, what is even more exciting, may provide us
with working models of the origin of life.

Until quite recently any consideration of life on the outer planets was
dismissed as not worthy of serious thought.  "Obviously" it was
ridiculous to talk about living creatures on worlds where the
temperature never rose to100 Fahrenheit, and the atmosphere contained
no oxygen, but consisted of suffocating or even poisonous gases.

This conclusion is probably correct, but it may be completely and
dramatically wrong, for the argument itself is certainly fallacious.
Far from being uninhabitable, it now appears that Jupiter may be even
more suitable for life than our own planet, at least according to some
optimistic biologists.

In the first place, the indicated temperature of Jupiter, as read by
instruments on our telescopes, is only that of the upper cloud layer.
The clouds of Venus are at50 degrees F."  but the surface beneath is
1,000 degrees hotter.  As we go down into the Jovian atmosphere, the
temperature will steadily rise; even that observed at the cloud layer
is higher than it should be, suggesting that the planet has some
internal source of heat and is not warmed only by the Sun.

So at some level water will be able to exist in the liquid state. There
may be seas on Jupiter that dwarf our oceans into puddles.

As for the atmosphere, it is now believed that life on Earth evolved in
precisely such an oxygen less environment of methane (CH4) and ammonia
(NH3), plus carbon dioxide and water.  (There was probably little free
hydrogen, as that would have escaped into space.) In a famous series of
experiments begun by Stanley Miller at the University of Chicago in
1953, it has been shown that such mixtures, in the presence of sunlight
or electrical discharges, inevitably and automatically produce a whole
range of very complex organic substances-the immediate precursors of
life itself.

It is now generally accepted that the first simple cells arose in this
warm, dilute soup and then evolved into plant forms.  At this point a
new situation arose, for plants liberate gaseous oxygen as a byproduct
of the manufacture of starch:

Water + carbon dioxide + sunlight = starch + oxygen

So, over millions of years, the composition of Earth's atmosphere began
to change from its original, "natural" state, until today it contains
about 21 per cent oxygen.  That this is really a very peculiar fact was
not realized until quite recently, owing to the human race's
understandable habit of taking the normal for granted.

An oxygen-bearing atmosphere is not normal.  Oxygen is so reactive-as
its use in rockets demonstrates-that one would not expect to find it in
the free state; it should have combined, by burning and rusting, with
the other elements.  Indeed, most of it has done so; over half the
crust of the Earth, by weight, is oxygen.

The coming of plant life reversed this process, liberating the free
element.  And because evolution always takes advantage of a changing
situation, the parasitic creatures we call animals duly
arrived-breathing the oxygen and eating the plants.  Evidence of this
is given by the fact that some primitive organisms not only do not need
oxygen, but are actually poisoned by it.  (Hence the treatment of
gangrene cases in oxygen chambers: the bacteria which produce this
condition are anerobic.) Even human beings are poisoned by pure oxygen
at pressures of more than two atmospheres, as divers with
oxygen-rebreathing gear have often found to their cost.

It is not true, therefore, that life requires oxygen.  Oxygen requires
life.

So all the conditions for the evolution of life may very well exist in
the gigantic, thoroughly stirred caldron of chemicals that is the
Jovian atmosphere.  It is true that the intensity of sunlight is low,
as compared with Earth, but this is nota fatal objection.  The far
higher level of electrical activity, as indicated by lightning flashes
which can sometimes be detected on simple transistor radios half a
billion miles away, may more than compensate for the lack of
sunlight.

Jovian life forms, if they exist, could be of any size from the
microscopic upward.  The high gravity would seem to favor small
creatures, but this limitation would apply only to land-dwellers.
Organisms that lived in the sea or floated in an atmosphere which might
be compressed to densities greater than that of most liquids could be
of any size.  And pressure itself, of course, is no handicap to life,
as is proved by the fragile sponges and starfish going about their
business in the Pacific trenches, under seven tons to every square
inch.

Perhaps the only useful generalization one can make about Jovian life
forms is that they would probably be very sluggish-more akin to the
vegetable than the animal kingdom.  They would have no choice, not
having access to the high-energy propellants that power the creatures
that run and jump and swim and fly on our planet.  The rocketlike
performances of our bodies are possible only because we can squander,
in a few minutes, the energy that plants have patiently accumulated
over many hours.

It would seem that the evolutionary road to high-energy or animal-type
organisms on Jupiter has been blocked by gravity, though in a rather
indirect manner.  The jovian atmosphere consists largely of hydrogen,
which has been unable to escape from the planet's gravitational clutch.
So even if free oxygen were liberated by any process, it would quickly
recombine with the excess hydrogen to form water.  There would be no
possibility of large amounts accumulating in the presence of so much
methane and hydrogen; at the very first lightning flash, the whole
atmosphere would explode.  Our planet bypassed this dilemma; any
hydrogen quickly leaked away into space, and the presence of large
amounts of inert nitrogen may also have prevented the formation of
unstable, explosive mixtures.  On such apparently random factors-the
difference between I g and 2%' g-do the destinies of worlds depend.

This argument against higher life forms must not be taken too
seriously.

The ingenuity of Nature appears unlimited; she may have found other
answers to the problem.  Certainly there are ample supplies of energy
on Jupiter, and biological systems may have found other ways of tapping
them besides oxidation.  Nor does it necessarily follow that life must
be fast-moving to be intelligent.

So Jupiter's twenty-five billion square miles of surface, plus almost
the same for the combined areas of Saturn, Uranus, and Neptune, may be
full of the most astonishing surprises.  Asimov's description of the
Solar System as

Jupiter plus debris may apply not only to its material but also to its
biological resources.  Our world may be a sparsely populated desert
compared to the seething fecundity that lies beyond the orbit of
Mars.

If the manned exploration of the giant planets is ever attempted, it
will require vehicles combining the attributes of spaceships and
bathyscaphes-not merely, as in the case of Venus, spaceships and
submarines.  Jupiter also presents a special, though not insoluble,
problem because of its high gravity.  A 160-pound man would weigh 400
pounds on

Jupiter and would have to spend most of his time immersed in water; the
three other giants have gravities that are slightly higher than Earth's
but that can probably be tolerated.

Even if the surfaces of these planets are inaccessible because of the
pressure, purely aerial expeditions might be worthwhile, as has also
been suggested for Venus.  One

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can imagine balloon-borne observatories drifting with the Jovian trade
winds judging by the disturbances that are visible from Earth, they
would have quite an exciting time.

Also, what does one put in a balloon that is to operate in an
atmosphere of hydrogen-the lightest gas that can possibly exist.  To
this there can be only one answer heated hydrogen.  It will indeed be a
strange twist of fate if the recently revived sport of hot-air
ballooning sees its fulfillment, a hundred years from now, in the
exploration of the outer planets.

What we do with the Solar System, in the centuries and the millennia
that lie ahead, will be the main -theme of future history.  We may
merely explore it; we may colonize it; we may even rebuild it.  The
time may come when all the inner planets have rings like Saturn, but
they will be rings of artificial moon lets the space cities of a
civilization that has regained the freedom from gravity that we lost
when we emerged from the sea.  Perhaps the drive into space is no more
than an unconscious, lemming like effort to regain that freedom.  If
this is true, the planets will merely provide the raw materials for a
largely space-borne culture.

Half a century ago Tsiolkovsky dreamed that mankind would move out from
the

Earth, tap the illimitable energies of the Sun (of which only one part
in two thousand million is now intercepted by our planet), and build
new worlds in the empty gulfs between the old ones.  But perhaps it has
all been done before; how disconcerting, if the asteroids turn out to
be an abandoned low-gravity housing project.

Here, in the table on the previous two pages, is the inventory of the
future-the immense but not infinite treasure of the Solar System,
waiting for us to use or to squander in the ages that lie ahead.

V. AROUND THE

UNIVERSE

OTHER SUNS THAN OURS

The Solar System, with its handful of planets scattered at immense
distances from the Sun, seems to consist almost entirely of empty
space.  Yet looked at from the cosmic viewpoint, it is a tiny, closely
packed affair.  Although interplanetary distances are a millionfold
greater than terrestrial ones, interstellar distances are a million
times greater still.  Even light, which can pass from the Sun to Pluto
in a few hours, takes more than four years to reach the nearest of the
stars.  It is not surprising, therefore, that it was quite late in
astronomical history before it was proved that the stars were actually
other suns, made pinpoints of light purely because of their enormous
distance.

Our Sun is a quite typical star, although it is a good deal brighter
and hotter than the average.  (Only three of the twenty nearest stars
exceed it in brilliance, and the vast majority are much fainter.) It is
one of a very large number-at least 100 billion-of stars forming a
roughly disk-shaped system known as the Galaxy.  If we could see our
Galaxy from outside, it would probably look not unlike Plate 61, which
is a photograph of the famous Andromeda Nebula.

The stars vary in size and brightness over a truly enormous range.
(Here we are referring, of course, to real variations, and not to those
caused merely by the effect of distance.) If, as is customary and
convenient, we take our Sun as a standard, then the biggest known stars
have a diameter a thousand times as great, so that they could 306 a
THE

PROMISE OF SPACE

enclose the orbits of all the planets right out to Saturn.  On the
other hand, the smallest stars have less than one hundredth of the
Sun's diameter, being thus smaller than the Earth.

The range of luminosity among the stars is even greater.  Stars a
million times as bright as the Sun are known, as well as stars 10,000
times fainter.  With these variations of brilliance go variations of
color.  Our

Sun, whose light we regard as normal, is actually a somewhat yellow
star.

The hottest stars of all shine with a brilliant bluish-white light, and
indeed the greater part of their radiation would be quite invisible to
us since it would lie in the ultraviolet, perhaps even in the X-ray,
region.

In descending temperatures the colors of the stars run: white,
yellow-white, yellow, orange-yellow, orange, deep orange-red.  There
are also suns of almost every possible intermediate color-gold, blue,
green, topaz, emerald-so that in the telescope some of the great star
clusters look like collections of jewels glittering against the
blackness of space.

As shown by Table 11, there are eight stars (two of them double) within
ten light-years of the Sun.  (This unit, the distance light travels in
a year, is a convenient one for measuring stellar distances.  It equals
5,880,000,000,000, miles.) Only one of our nearest eight neighbors is
visible without a telescope in the northern hemisphere; this is Sirius,
the brightest star in the sky, about nine light-years away.  (The
closest of all stars is the very faint Proxima Centauri, quite
invisible to the naked eye despite its distance of "only" 4.3
light-years.)

Our Sun is in a moderately well-populated region of the Galaxy, though
nowhere near its center.  On a clear moonless night the sky seems full
of stars more or less equally distributed around the heavens, with the
pale band of the Milky Way wandering through them.  This faint arch of
light, which continues around the southern hemisphere and so divides
the sky into almost equal parts, was a mystery to mankind until the
invention of the telescope revealed that it was composed of millions of
faint stars.  We now know that their faintness is due only to distance,
and the reason why they form a continuous band around the Earth arises
purely from our location in space.  When we look toward the Milky Way,
we are looking along the major axis of the Galaxy, so that we see the
stars packed in endless ranks as far as the eye, or even the
telescope,

can see.  When we look in other directions, however, our gaze quickly
passes out through the Galaxy's relatively thin disk and we can see
only a few stars-and beyond those the great emptiness in which the
other island universes float.  As a glance at Plate 61 will
demonstrate, anyone living on a planet in the outskirts of the
Andromeda Nebula would see a very similar band of stars around the
sky

TABLE 11

THE TWENTY NEAREST STARS

DISTANCE, BRIGHTN SS

NAME LIGHT-YEARS(SUNCOLOR

1. Sun 01.0Yellow 2..  Centauri A 4.31.0Yellow 3. a Centauri B
4.30.28Orange 4..  Centauri C (Proxima) 4.30.00005Red 5. Barnard's star
6.00.0004Red 6. Wolf 359 7.70.000017Red 7. Luyten 726-BARed 8. Luyten
726-8B 7.90.00003Red 9. Lalande 21185 8.20.0048Red 10. Sirius A
8.723.0White 11.  Sirius B 8.70.008White 12.  Ross 154 9.30.00036Red
13.  Ross 248 10.30.0001Red 14.  e Erldani 10.80.250range 15.  Ross 128
10.90.0003Red 16.  61 Cygni A 11.10.052Orange 17.  61 Cygni 6
11.10.028Orange 18.  Luyten 789-6 11.20.00012Red 19.  Procyon A
11.35.8White 20.  Procyon 8 11.30.00044Red

The heart of our own Galaxy, where the stars are clustered together
more thickly than they are in the neighborhood of the Sun, lies toward
the constellation Sagittarius.  Plate 62 gives some idea of the great
star clouds in one of the denser regions of the

Milky Way, which in addition to suns contains immense clouds of
luminous gas-perhaps the raw material from which the stars are made.

Although the study of the stars themselves is a fascinating and
never-ending pursuit, from the viewpoint of as Plate 61.  Pictures
relayed by Mariner 6 on July 31, 1969, show the rugged

Martian terrain from 3125 miles up.  The photos revealed a previously
unsuspected region at chaotic, jumbled ridges.  NASA

tronautics we are interested only in planets.  Unfortunately, the
greatest of planets would be totally invisible at a distance of a few
light-years, so we do not know if even Proxima Centauri has worlds
revolving around it.  Our views on the existence of planets in the
universe are likely, for the time being, to be determined by whether we
think the Solar System to be something usual, or an astronomical
freak.

Until quite recently the latter opinion was generally held, because the
only conditions under which anyone could imagine the Solar System
forming seemed to demand very unusual circumstances, such as the
near-collision of two stars.  Today quite a different outlook prevails.
We are still by no means sure how planets are formed, but it is felt
that many, if not most, stars may possess them.  Certainly among the
100 billion stars of this

Galaxy alone, there musi be myriads with solar systems.  But as to
which are the stars with planetary companions and which are alone,
there is as yet no reliable way of discovering.  This is a problem
which may be solved when we can build observatories in space.

In a very few exceptional cases there is some evidence of bodies of
planetary size revolving around other stars.  The first to be
discovered was in the system of the double star 61 Cygni, about eleven
light-years away.

This pair of faint stars has been carefully studied for more than a
century, and from the movements of one component the existence of a
third body has been deduced.  This object has about 15 times the mass
of Jupiter, or 5,000 times that of Earth.  It seems too small to be a
sun and may therefore be a very large planet.

In 1960 a slightly larger companion was discovered circling another
nearby star, Lalande 21185, and in 1964 came perhaps the most
remarkable discovery of all-an object only 50 per cent heavier than
Jupiter, and thus almost certainly a planet, orbiting around the faint
red dwarf known as Barnard's star.

Barnard's star, six light years away, is the second -closest star;
Lalande 21185 the fifth, 61 Cygni the eleventh.  It is important to
realize that only the very largest planets can possibly be discovered
by this means; a world as small as Earth would be a thousand times too
light to be detected.

Yet despite this limitation, three such bodies have been found among
the eleven nearest stars, so it can hardly be

Plate 62.  Star clouds in the Milky Way, Sagittarius region.  Mount
Wilson and Palomar Observatories doubted that there must be many
others.  Solar systems may be almost as common as suns.

Another line of evidence also suggests that this is the case; When the
total "spin" (or angular momentum) of the Solar System is added up, it
is found that most of it resides in the planets-not in the Sun itself,
despite its far greater mass.  The Sun, in fact, appears to be rotating
with abnormal slowness, as though it has exhausted itself with the
effort of throwing off the planets.

It is possible, by means of the spectroscope, to measure the spin, or
rotational velocity, of.  the stars, even though they appear as
dimensionless points of light.  When they are classified in what is
believed to be increasing order of age, it appears that there is an
abrupt loss of spin in early youth, and the simplest explanation is
that planets are born at this stage.

Our Sun is, apart from its planets, a solitary wanderer through space.
Many stars, however, occur in pairs, revolving around each other under
their mutual gravitation.  The variety of these partnerships is
immense; sometimes the two stars are of identical types, but sometimes
they are so disproportionate in size that an elephant waltzing with a
gnat would not be an inaccurate comparison.

Systems of three, four, five, six, or even more suns occur, often with
fantastic and beautiful combinations of color.  (The nearest star is
one of a triplet-Alpha Centauri A, B, and C; the latter is sometimes
known as

Proxima, since on occasion it is slightly closer to us than its larger
companions.) Although planets may occur in such systems, in many cases
they would undergo such violent changes in temperature that they would
be uninhabitable.  Their orbits would be exceedingly complex, sometimes
even weaving from one star to another, so that our concept of a "year"
would be utterly meaningless.  The problem of contriving a calendar for
such worlds would be an appalling one-even worse than for Mercury (see
Chapter 22)-but in compensation, any inhabitants would have skies whose
splendor we can scarcely imagine.

Even more incredible would be the view of the heavens from a planet
near the heart of a globular cluster.  These are great spherical swarms
of stars, so closely packed toward the center that the separate suns
must be only light-weeks apart, as against the light-years that
normally lie between stars.  There could be no such things as night and
darkness on any worlds at the core of a globular cluster: the sky would
be a continuous blaze of multicolored light.  The dwellers of such
worlds would have a very limited knowledge of astronomy, for they would
be unable to observe the structure of the universe through the screen
of stars which hid them from the rest of space (Plate 63).

Stars vary greatly among themselves in physical structure, as well as
in size and brilliance.  Some of the giants are so rarefied that they
are a million times less dense than our atmosphere: they have been
picturesquely christened "red-hot vacuums."  At the other extreme are
stars whose density is thousands of times greater than any substance on
Earth.  The best-known example of these "White Dwarfs" is the Companion
of Sirius (Sirius B), with a density six thousand times that of lead. A
matchbox of this star's material would weigh a couple of tons-but it
should be pointed out that if one did, by some miraculous means, obtain
a match boxful it would not stay that size for even a millionth of a
second.  Its density is produced by the enormous temperatures and
pressures inside the star, and if these were removed it would explode
with a violence probably eclipsing that of an atomic bomb.

Something of this kind may indeed happen occasionally, for detonating
stars (novae) are frequently observed.  At rare intervals they are
conspicuous enough to be really prominent objects, and one (Tycho's
nova, 1572) was so brilliant that for some weeks it was visible in
broad daylight.

The cause of this gigantic stellar explosion is unknown; in its most
spectacular form, a star will, within a few hours, increase its
brilliance a bun dred-million-fold and may even, for a short while,
outshine all the other suns in its universe added together.  These
supernovae are relatively infrequent, but ordinary novae are quite
common, and one cheerful theory suggests that all suns may become novae
at some time or other during the course of their evolution.  As far as
the inhabitants of any planets were concerned, the final result would
be much the same whether their sun became a nova or a supernova.  The
difference would be, roughly speaking, that between being slowly melted
or swiftly vaporized.

There are also large numbers of stars (variables) whose brilliance
fluctuates over a more modest range.  Some of these stars appear to be
pulsating, and they go through their cycle of brightness with clockwork
precision.  Others show no regularity in their variations; they behave
like great, flickering bonfires, sometimes quiescent, sometimes flaring
up for days or years, then relapsing again.

Such changes, as long as they were not too great, would not rule out
the possibility of life on any planets of these stars.  They would
simply have complicated seasons predictable in the case of the regular
variables but quite erratic for the irregulars.

It would always be possible, as far as the stars which shine with a
steady light are concerned, for planets with temperatures between the
boiling and melting points of water to exist.  They might have to be
very close to some of the cooler stars and a long way from the
brilliant blue-white suns.  This would mean that their "year" might be,
in the one case, only a few terrestrial days, and in the other, perhaps
thousands of our years.

All the stars, including of course our Sun, are in motion through
space.

Their movements are not entirely random, for the great disk of the
Galaxy is rotating, sweeping the stars around with it and completing
one revolution in about 200 million years.  Since our planet was
formed, therefore, the Sun has made only about twenty circuits of the
Milky Way.

This slowly turning disk of stars is about 100,000 light years in
diameter, and its greatest thickness is perhaps one-fifth of this.  In
the neighborhood of the Sun (about two-thirds of the way toward the
rim) the thickness of the great lens-shaped system of stars is about
10,000 light years-though it has, of course, no definite boundaries.

As we look out past the thinly scattered stars away from the plane of
the

Milky Way, we can see, at immense distances, the other galaxies.  Some
we observe turned full toward us, like great catherine wheels of stars,
showing intricate and still unexplained spiral structures.  Others are
edge-on; still others, like the Andromeda Nebula are tilted at an
angle.  As we look at Andromeda, the stars scattered closest to us are
the relatively close suns of our local system.  We can look past them,
and across the immensity of intergalactic space, as a town-dweller
might look past the streetlamps of his suburb to the lights of another
city, many miles away.

The Andromeda Galaxy is the nearest of the other

Plate 63.  A globular star cluster.  Mount Wilson and Palomar
Observatories

universes and it is about 2 million light-years away.  In whatever
direction we look (except those in which clouds of obscuring matter
block our view), we see other galaxies, extending to the limits of
telescopic vision.  They appear to be roughly the same size as our own
system, and on the average their distances apart are of the order of a
million light-years (though local clusterings occur).  It will be seen
that there is a breakdown here of a law which has applied so far in the
architecture of the cosmos.

The distances between stars and planets were hundreds of thousands of
times greater than the dimensions of these bodies themselves.  Yet the
distances between the galaxies are only about ten times as great as
their diameters.

The limit which we can reach with the most powerful telescope (the
200-inch reflector on Mount Palomar) is perhaps ten billion
light-years.  So far, the galaxies show no signs of thinning out or of
forming more complex structures.  It is possible that we have come to
the end of the hierarchy, but this is a matter concerning which we can
only speculate at the moment.

In the next few decades-thanks to quasars, orbiting telescopes, and
other developments still unforeseen-we sba ll have a great deal of
fresh information, and the pattern of the cosmos as a whole may be
taking clearer shape.  We may have discovered that space is infinite,
and the galaxies extend onward forever, or we may have proved that it
is curved and of limited volume, so that although the total number of
galaxies will be immense, it will nevertheless be finite.  These
questions of cosmology are, however, outside the scope of this book;
let us return to our own galactic system, the Milky Way.  if we assume
that only one sun in a thousand has planets-and this may well be a
gross underestimate-that would give a total of perhaps a hundred
million solar systems in our Galaxy alone.  Among all these, it can
hardly be doubted that there would be many worlds on which life of some
kind would be possible; there would even be a large number which would
have physical conditions similar to those of Earth.

A few decades ago, such speculations, fascinating and

-The word "universe" is employed here in the restricted sense of a
single galaxy.  Thus "our universe" is merely the Milky Way system.
Astronomers usually employ the word "cosmos" to describe the whole of
creation, i.e., all the galaxies.

Plate 64.  Spiral nebula in Ursa Major.

Mount Wilson and Palomar Observatories irresistible though they might
be, seemed of no practical value.  Almost any scientist in the world
before the 1950's, would have stated that there was no possibility that
we could ever learn anything about the existence of life in other
planetary systems.

In 1835 the philosopher Auguste Comte came to an even more forthright
conclusion.  In his Cours de Philosophic Positive, be attempted to
define the limits within which scientific knowledge must always lie,
and he made this statement regarding the heavenly bodies:

We see how we may determine their forms, their distances, their bulk,
their motions, but we can never know anything of their chemical or
mineralogical structure; and much less, that of organized beings living
on their surface.  .

Within a generation the spectroscope had utterly refuted the first part
of this dictum, and the "chemical structure" of the stars become the
dominant theme of astrophysics.  Soon the mineralogy of the Moon and
planets will be of prime scientific, and practical, importance.

And now there is every reason to believe that the last part of M.
Comte's pronouncement will be equally untrue.

ACROSS THE ABYSS

The subject of interstellar communication-if not transportation-became
suddenly respectable soon after the first artificial satellites were
launched.  This is certainly no coincidence; the intellectual climate
now allowed scientists to discuss such ideas without risking their
reputations.

A striking example of the change that had taken place in little over
twenty years will be found in the pages of the famous scientific
journal Nature.  In the 1936-39 period it printed several highly
critical reviews of books and articles on such modest projects as the
journey to the Moon; but in 1959 it published the first of an already
classical series of papers on interstellar communication and superior
cosmic societies.

These papers pointed out that developments in radar and its direct
scientific offspring, radio astronomy, have now given us the technology
with which we can signal to the stars.  This has happened in a very
short time, historically speaking, so it seems reasonable to assume
that, if there are other technically advanced societies much older than
ours, interstellar signaling should be child's play to them.  But as it
is much easier, cheaper, and perhaps safer to receive than to transmit
signals, we should start to listen to the universe before we attempt to
talk to it ourselves.  (It would be too bad, of course, if everybody
has come to the same conclusion, and the Galaxy is full of patient
listeners and no talkers.)

The problem of sending a radio signal over interstellar distances is
one that can be precisely defined in terms ota 319

320 * '1711E PROMISE OF SPACE

relatively few variables.  Basically, they are the distance, the power
available, the narrowness of the beam, the size of the receiving
antenna, the sensitivity of the receiver, and the rate at which
information is transmitted.

As far as the first is concerned, we have now established contact with
space probes more than a hundred million miles from Earth.  Only a few
of the closer stars are within a million times this distance, and as
signal strength weakens with the square of the range, this means that
the problem of sending a signal to, say, Altair (sixteen light years
away) is about a million mil hon times more difficult than contacting a
Mariner spacecraft when it is halfway around the Sun.

One can compensate for distance with increased power, but an increase
of a million million times is out of the question; it would mean
putting more than the entire electrical output of the Earth into the
transmitter.  However, the situation is not quite as bad as this, for
Mariner had a very small antenna-only about 4 feet across-and we can
assume that one of at least 100 times that diameter, and hence 10,000
times the area, would be used by any interstellar receiver.  In fact,
even this may be unduly modest, as radio telescopes up to 1,000 feet in
diameter have already been built.

Using shorter waves also improves the situation by giving narrower
beams, so that less energy is wasted.  So does reducing the rate of
signaling to a low level; it takes thousands of times more energy to
transmit a television picture than a few dots and dashes, which are all
that would be required for the first attempts at interstellar
contact.

When all these points are taken into account, it appears that, with a
slight extension of existing technology, we could send detectable
signals to a distance of at least a hundred ligbt-years-that is, over a
volume of space containing many thousands of stars.  And when we can
establish transmitters in space, or on the Moon.  clear of the Earth's
absorbing atmosphere, we will be able to do very much better; for then
we will be able to use the fantastically narrow beams made possible by
the laser.

But this argument assumes that there is a fully cooperative party at
the receiving end, listening in at the right frequency, with the
appropriate equipment, and with an antenna system aimed at the correct,
microscopically small portion of the sky.  The odds against this are,
of course, so enormous that they might seem to be infinite.

In a famous letter to Nature, published in 1959 ("Searching for

Interstellar Communications"), the physicists Giuseppe Cocconi and
Philip

Morrison pointed out a way of improving the odds.  They argued that
there is one specific radio frequency which would be familiar to every
science-orientated civilization in the universe and on which one might
therefore expect to find listeners.  The magic frequency is 1420
megacycles second, corresponding to the rather short wavelength of 21
centimeters.  It is unique, characteristic, unmistakable-standing out
against the general radio din of the universe as a pure and very
intense musical note might be audible in the cacophony of a boiler
factory.  On this planet we have already spent millions of dollars
building equipment to trap waves of this frequency, for reasons that
have nothing to do with interstellar communication.  Other cultures, if
they are remotely like ours, might be expected to do the same.

This unique radiation is that emitted by hydrogen atoms in space; it is
their natural call sign, or station identification.  Most of the
universe consists of hydrogen, and by studying these waves radio
astronomers have been able to work out details of galactic structure
that could not be obtained in any other manner.  If there are any radio
astronomers on other planets, Dot only will they be doing exactly the
same thing, but they too may have concluded that they are not alone in
doing it.  So if any wish to announce their presence, they might be
expected to signal at this frequency-or, possibly, at exactly half, or
exactly twice, its value, to avoid interference with the natural
21-centimeter omission.

Cocconi and Morrison therefore suggested that it might be worthwhile to
aim our largest radio telescopes at some of the nearer stars, and to
listen out at 1420 megacycles second  Although a successful outcome
would be very unlikely, the matter was of such importance that it was
worth a considerable effort.  And, if we never searched, the chance of
success would certainly be zero.

With this encouragement, a number of radio astronomers (probably more
than have confessed to it) have made tentative searches with limited
equipment; as far as is known, none of the really big telescopes has
been used for this purpose.  Probably thousands of hours of radio
listening, to hundreds of selected areas of the sky, will have to be
carried out before any verdict can be obtained.  This would cost
millions of dollars-and, of course, a negative result would prove
nothing.  It is a sobering thought that not one of the cultures which
produced Akbenaton,

Confucius, Buddha, Plato, Christ, Dante, Shakespeare, Leonardo,
Newton,

Beethoven, Darwin, Einstein, could have made its presence known even as
far away as the Moon.  Not until the development of the first
high-powered radars in the mid-1940's was there any possibility that
intelligent life on Earth could be detected at interstellar distances,
and then only by the wildest chance.

It is conceivable, though unlikely, that the use of radio for
long-distance communication may be only a brief, passing phase in the
development of a technological culture-a stepping-stone between smoke
signals and something that we cannot imagine today.  In this case, only
a minute percentage of interstellar civilizations-those occupying our
century-wide slot on a million- or even billion year band-would be in a
position to communicate with us.  However, if more advanced races are
interested in announcing their presence to undeveloped planets,
presumably they would set up a few primitive mega megawatt radios for
this very purpose.  It is the sort of project that might keep the
children amused.

Other far more ambitious schemes for attracting attention over
interstellar distances have been proposed.  A large thermonuclear
explosion, for example, has unique characteristics that enable it to be
distinguished from natural phenomena; a series of explosions at
precisely timed intervals would be proof positive of an advanced
technology.  However, it would be difficult, and certainly expensive,
to send useful information in this manner.

A very advanced civilization might "label" its sun by dumping into its
atmosphere vast quantities of artificial elements which did not occur
in nature, so that their spectral lines would convey an unmistakable
message to other astronomers; in some cases, the amounts of matter
needed would be a few hundred thousand tons-no tan unreasonable figure.
Or a series of occulting screens might be put in orbit, so that a star
became a celestial lighthouse, blinking across the ocean of space.

Soviet scientists have shown particular enthusiasm for this type of
speculation and have taken it to daring lengths.  The astrophysicist N.
S. Kardashev, for example, has suggested that after a technical
civilization has endured for a sufficiently long period, it should be
able to control energy resources equal to the output of its sun say
500,000,000,000,000,000,000 bp (our civilization's current resources
are only about 50,000,000,000 hp).  And there may even be civilizations
able to control the energy output of an entire galaxy; expressed in
horsepower, this is a number with 34 zeros.

If such societies exist, we should be able to detect their activities
over most of the observable universe.  Not merely their deliberate
attempts at signaling, but what might be called their civil-engineering
projects, would be apparent over cosmic distances.  We should,
therefore, be on the watch for astronomical phenomena, and perhaps even
stellar configurations, which do not appear to have a natural
explanation.

These ideas have been taken perhaps' to their limit by Dr.  Freeman
Dyson of the Institute for Advanced Studies, Princeton.  Dyson points
out that as our

Galaxy appears to be at least 10 billion years old, any really ancient
civilization with a history of continuous technological development
will have had ample time to take it over and reconstruct it, should it
feel so inclined.  However, as far as we can see, the Galaxy is still
in what Dyson calls the "wild" state.  It has not yet been turned into
a well-kept cosmic park.

So perhaps there are no really advanced civilizations only ones a few
thousand years ahead of us.  Yet, when we look back at the changes that
have taken place on our planet in a mere moment of historic time (it
has been only 400 years since men were burned for saying that the Earth
is not the center of the universe), we may well wonder if we will find
anyone near enough our level of development to talk to us in language
we can understand.

What that language might be is another problem that has engaged a good
deal of attention.  Even if we established radio contact with another
species, we would be rather like two prisoners in adjacent cells,
trying to exchange messages by tapping on the walls-and neither knowing
a word of the other's language.

In such a situation, is any meaningful communication even theoretic
ally possible?  The answer is yes-if the two parties are sufficiently
intelligent and sufficiently patient.

Philologically minded scientists have already had a good deal of fun
working out possible codes, which might lead from "I + 1 = 2" up to the
highest levels of abstract thought.  (I have even seen one attempt to
explain modern poetry to an extraterrestrial.  I did not understand
it.)

The problem would be much simplified if pictorial information could be
transmitted, and there are many ways of doing this.  Radio astronomers
are fond of constructing 11 messages" out of strings of ones and
zeros-the equivalents, say, of radioed dots and dashes-and sending them
to their friends to see if they can decinher them.  For example, Dr.
Frank Drake once mailed his colleagues a series which began:
111100001010010000 .. . and so on for a total of 551 digits.

If we received such a message from space, reneated several times,
undoubtedly our first reaction would be to look at the curious number
551.

It does not take much effort to discover that it is the product of two
prime numbers, 19 and 29.  The obvious step then-or so it seems to us
of the

TV age, though perhaps a medieval monk or a Greek philosopher might not
think of it-is to arrange the ones and zeros as black and white squares
in a 19-by-29 grid, to see if any kind of pattern emerges.

This can be done in only two possible ways, with either 19 or 29
squares horizontal.  In Dr.  Drake's example, one arrangement gave a
meaningless jumble, but the other resulted in an obvious and clear cut
picture of a biped surrounded by geometrical symbols.

It is clear that by such methods a great deal of information could be
transmitted, though to what extent full communication at all
intellectual and emotional levels could be attained is a question that
completely transcends technology.  (We are still trying to decide if
the dolphins are saying anything to us, and we can touch them.) In the
cosmic case, we are also limited by the fact that no true conversation
would be possible; there would be none of the quick feedback-the
process of question and answer which is so essential for understanding
between different individuals here on

Earth.

This is an inevitable result of the distances between the stars.  If we
sent a radio signal to Proxima Centauri, it would be almost nine years
before we could possibly get a reply.  A more probable time lag would
be decades or centuries.  If the nearest radio-using civilization is at
the center of the

Galaxy, any message we received from it today would be coming from ten
times farther back in the past than the siege of Troy.

Interstellar radio communication, therefore, will be a very tedious
business-a research project for the centuries.  This would not be a
great disadvantage for a long-lived, scientifically oriented
civilization, which might be conversing with dozens of other cultures;
eventually, even at the limiting speed of light, there would be time
for any amount of back-and-forth discussion.  But the scholars who
asked the questions would never live to hear the answers.

Even so, they would be much better off than the archaeologists, who can
never ask questions at all.  How much more we should know of history
if

Gibbon had been able to interrogate the Caesars and Toynbee had
received their replies.  This is a rough analogy of the situation that
may arise in interstellar dialogues.

There are many scientists who profess themselves quite satisfied with
this state of affairs; there is no need, they say, to go traveling
around the universe if we can send messages which are far cheaper,
quicker, and safer in every way.  Some, making a virtue of necessity,
have even argued that the effective quarantine of the interstellar
distances is a good thing.  The various races in the Galaxy can
exchange information, but they can never do.  each other any harm
through physical contact.

This is really a very naive attitude, rather like that of Auguste Comte
quoted in the last chapter.  It assumes that the limits of
technological progress are already in sight; one would have thought
that by this time no scientist with the slightest knowledge of history
would fall into such a trap.

In a celebrated lecture at Brookhaven ("Radioastronomy and
Communication

Through Space") Dr.  Edward Purcell once remarked that "all this stuff
about traveling around the universe ... belongs back where it came
from, on the cereal box."

Dr.  Purcell should have remembered that this is just where most talk
of travel to the Moon was only a generation ago.  114do

TO THE STARS

Travel to the stars is not difficult, if one is in no particular hurry.
As we have seen in Chapter 24, today's vehicles could send substantial
payloads to Proxima Centauri, especially if they went by way of
Jupiter.

Unfortunately, the voyage would take the better part of a million
years.

However, no one doubts that there will be enormous increases in
spacecraft velocities, especially when we have discovered really
efficient ways of harnessing nuclear energy for propulsion.
Theoretically, a rocket operating on the total annihilation of matter
should be able to approach the speed of light-670 million mph.  At the
moment, we can reach about 1/20,000 of this figure; clearly, there is
plenty of room for improvement.

Let us be very pessimistic and assume that rocket speeds increase
tenfold every century.  By the year 2000 we will certainly have
vehicles which could reach the nearer stars in 100,000 years,
carrvilicy really useful payloads of automatic surveying equipment.

But there would be no point in building thej-n, for we could be sure
that they would be quickly overtaken by the ten-times-faster vehicles
we would be building a hundred years later.  And so on.

The situation, in round figures, might look something like this:

Clearly, there is no point in making anything but paper studies until
about the year 2300; but after that, it is time to start thinking about
action.

A wealthy, stable, scientifically advanced society would be accustomed
to making

LAUNCH DATE TIME TO PROXIMA CENTAURI (YEARS)

2000 100,000 2100 10,000 2200 1,000 2300 100 2400 10

bun dred-year plans, and it might well consider building space probes
to survey the nearer stars, as our Mariners have surveyed Mars and
Venus. They would report back along tight laser beams to gigantic
reflecting telescopes orbiting the Earth; or they might even come back
themselves, loaded with quantities of information too enormous to be
transmitted across the light-years in a period less than their own
transit time.

This proxy exploration of the universe is certainly one way in which it
would be possible to gain knowledge of star systems which lacked
garrulous, radio-equipped inhabitants; it might be the only way.  For
if men, and not merely their machines, are ever to reach the planets of
other stars, much more difficult problems will have to be overcome.
Yet, they do not appear to be insoluble, even in terms of the primitive
technology we possess today.

We will first of all assume-and the evidence is overwhelmingly in favor
of this-that it is impossible for any material object to attain the
velocity of light.  This is not something that can be explained; it is
the way that the universe is built.  The velocity of light represents a
limit which can be more and more closely approached but never reached.
Even if all the matter in the cosmos were turned into energy and that
energy were all given to a single electron, it would not reach the
speed of light, but only 99.9999999999-and so on, for about 160
digits-per cent of it.

We may eventually be able to build rockets driven by the total
annihilation of matter, not the mere fraction of a per cent that is all
we can convert into energy at present.  No one has the faintest idea
how this may be done, but it does not involve any fundamental
impossibilities.  Another idea that had been put forward is that, at
very high speeds, it may be possible to use the thin hydrogen gas of
interstellar space as fuel for a kind of cosmic, fusion powered ramjet.
This is a particularly interesting scheme, as it would give virtually
unlimited range, and remove the restrictions imposed by an onboard
propellant supply.  If we are optimistic, we may guess (and guessing is
all that we can do at this stage) that ultimately speeds of one tenth
of that of light may be attained.  Remember that to make even a one-way
voyage, this would have to be done twice-once to build up velocity, the
second time to discard it, which is just as difficult and expensive.
(Atmospheric braking is not going to work very well at 70 million mph.
Even at I g it would take many times the width of the Solar System to
slow down from such a speed.

On this assumption, we will be able to reach the nearer stars in a few
decades, but any worthwhile explorations would still have to last
thousands of years.  This has led some scientists to make the striking
pronouncement:

Interstellar flight is no tan engineering problem, but a medical one.

Suspended animation may be one answer.  It requires no great stretch of
the imagination to suppose that, with the aid of drugs or low
temperatures, men may be able to hibernate for virtually unlimited
periods.  We can picture an automatic ship with its oblivious crew
making the long journey across the interstellar night until, when a new
sun was looming up, the signal was sent out to trigger the mechanism
that would revive the sleepers.  When their survey was completed, they
would head back to Earth and slumber again until the time came to
awaken once more and greet a world which would regard them as survivors
from a distant past.

Another solution was first suggested, to the best of my knowledge, in
the 1920's by Professor J. D. Bernal in a long-out-of-print essay, The
World, the Flesh, and the "Devil, which must rank as one of the most
outstanding feats of scientific imagination in literature.  Even today
many of the ideas propounded in this little book have never been fully
developed, either in or out of science fiction.

Bernal imagined entire societies launched across space, in gigantic
arks which would be closed, ecologically balanced systems.  They would,
in fact, be miniature planets upon which generations of men would live
and die so that one day their remote descendants would return to Earth
with the record of their celestial Odyssey.

To The Scars 0 329

The engineering, biological, and sociological problems involved in such
an enterprise would be of fascinating complexity.  The artificial
planets (at least several.  miles in diameter) would have to be
completely self-contained and self-supporting, and no material of any
kind could be wasted.

Commenting on the implications of such closed systems, Time magazine's
science editor, Jonathan Leonard, once hinted that cannibalism would be
compulsory among interstellar travelers.  This would be a matter of
definition; we crew members of the three-billion-man spaceship Earth do
not consider ourselves cannibals, despite the fact that every one of us
must have absorbed atoms which once formed part of Caesar and
Socrates,

Shakespeare and Solomon.

One cannot help feeling that the interstellar ark on its 1,000-year
voyages would be a cumbersome way of solving the problem, even if all
the social and psychological difficulties could be overcome.  (Would
the fiftieth generation still share the aspirations of their Pilgrim
Fathers, who set out from Earth so long ago?) There are, however, more
sophisticated ways of getting men to the stars than the crude,
brute-force methods outlined above.

The ark, with its generations of travelers doomed to spend their entire
lives in space, was merely a device to carry germ cells, knowledge, and
culture from one sun to another.  How much more efficient to send only
the cells, to fertilize them automatically some twenty years before the
voyage was due to end, to carry the embryos through to birth by
techniques already foreshadowed in today's biology labs-and to bring up
the babies under the tutelage of cybernetic nurses who would teach them
their inheritance and their destiny when they were capable of
understanding it.

These children, knowing no parents, or indeed anyone of a different age
from themselves, would grow up in the strange artificial world of their
speeding ship, reaching maturity in time to explore the planets ahead
of them perhaps to be ambassadors of humanity among alien races, or
perhaps to find, too late, that there was no home for them there.  If
their missions succeeded, it would be their duty (or that of their
descendants, if the first generation could not complete the task) to
see that the knowledge they had gained was someday carried back to
Earth.

Would any society be morally justified, we may well ask, in planning so
onerous and uncertain a future for its unborn-indeed, un
conceived-children?  That is a question which different ages may answer
in different ways.  What to one era would seem a coldblooded sacrifice
might to another appear a great and glorious adventure. There are
complex problems here which cannot be settled by instinctive, emotional
answers.

At the moment, our whole attitude to the problem of interstellar travel
is conditioned by the span of human life.  There is no reason
whatsoever to suppose that this will always be less than a century, and
no one has ever discovered just what it is that makes men die.  It is
certainly nota question of the body "wearing out" in the sense that an
inanimate piece of machinery does, for in the course of a single year
almost the entire fabric of the body is replaced by new material.  When
we have discovered the details of this process, it may be possible to
extend the life span indefinitely if so desired-and this would
drastically reduce the size of the universe from the psychological
point of view.

Whether a crew of immortals, however well balanced and carefully chosen
they might be, could tolerate each other's company for several
centuries is an interesting subject for speculation.  But the mobile
world let in which they would travel might be larger-and would have
incomparably greater facilities in every respect-than the city of
Athens, in which small area, it may be recalled, a surprising number of
men once led remarkably fruitful lives.

If medical science does not provide the key to the universe, there
still remains a possibility that the answer may lie with the engineers.
We have suggested that one tenth of the speed of light may be the best
we can ever hope to attain, even when our spacecraft have reached the
limit of their development.  A number of studies suggest that this is
wildly optimistic, but these are based on the assumption that the
vehicles have to carry their own energy sources, like all existing
rockets.  It is at least conceivable that the interstellar ramjet may
work, or that it is possible to supply power from an external device,
such as a planet-based laser, or that the universe contains

0 See.  the papers by Sebastian von Hoerner and Edmund Purcell in the
volume

Interstellar Communication, ed."  A. G. W. Cameron ( 1963).

still unknown sources of energy which.  spacecraft may be able to tap.
In this case, we may be able to approach much more, closely to the
speed of light, and the whole situation then undergoes a radical
change.  We become involved in the so-called time-dilation effect
predicted by the Theory of

Relativity.

It is impossible to explain why this effect occurs without delving into
very elementary yet subtle mathematics.  (There is nothing at all hard
about basic relativity mathematics; most of it is simple algebra.  The
difficulty is all in the underlying concepts.) Nevertheless, even if
the explanation must be bypassed, the results of the time-dilation
effect can be stated easily enough in nontechnical language.

Time itself is a variable quantity; the rate at which it flows depends
upon the speed of the observer.  The difference is infinitesimal at the
velocities of everyday life, and even at the velocities of normal
astronomical bodies.  It is all-important as we approach to within a
few per cent of the speed of light.  To put it crudely, the faster one
travels, the more slowly time will pass.  At the speed of light, time
would cease to exist; the moment "now" would last forever.  Let us take
an extreme example to show what this implies.  If a spaceship left
Earth for Proxima Centauri at the speed of light and came back at once
at the same velocity, it would have been gone for some eight and a half
years according to all the clocks and calendars of Earth.  But the
people in the ship, and all their clocks or other time-measuring
devices, would have detected no interval at all.  The voyage would have
been instantaneOUS.

This case is not possible, even in theory.  But the one that follows
does not involve any physical impossibility, though its achievement is
so far beyond the bounds of today's-or tomorrow's-technology that it
may never be realized in practice.  Nevertheless, since it illustrates
the working of the universe, it is worth careful study.

Imagine a spaceship that leaves the Earth at a comfortable I-g
acceleration, so that the occupants have normal weight.  Today's
rockets could maintain this rate for about twenty minutes, but we will
assume that our Xpowered supersbip can keep it up indefinitely.  Its
velocity and its distance from Earth would increase as follows:

The last line of the table is in parentheses, as after one

TABLE 12

I-G VOYAGES

VELOCITY, DISTANCE,

DURATION MPH MILES

1 hour 80,00040,000 1 day 1,900,00023,000,000 1 week
13,000,0001,100,000,000

I month 57,000,00022,000,000,000 1 year
(675,000,000)(3,000,000,000,000)

year at 1-g acceleration the ship would have exceeded the velocity of
light (670 million mph) according to this straightforward,
nonrelativistic calculation, and this is impossible.  Professor J.B.S.
Haldane once remarked to me, half seriously, that perhaps nature
intended us to be interstellar voyagers, since one year at 1-g was a
reasonable price to pay, even for organisms living only 70 years, to
attain almost the speed of light.

But, of course, one has to slow down again to complete any desired
journey, and deceleration requires exactly as much time-and distance-as
acceleration.  It would require one year of each, plus three years of
coasting at peal, velocity, to make the four-light-year trip to the
nearest star, Proxima Centauri.

Even if we could exceed the speed of light, the journey could not be
made much more quickly, at a comfortable 1-g acceleration and
deceleration.  If the coasting period was eliminated, and the ship went
on gaining speed until mid-voyage (when it would be moving at twice the
velocity of light) the total transit time would be reduced only by one
year, from five years to four.

Higher accelerations could be endured-if the passengers spent the whole
journey floating in liquid or frozen in blocks of ice.  Or we might
assume the invention of the famous "space-drive" that acts upon every
atom of matter in its domain, so that it could produce acceleration
without any apparent force.  (As gravity does precisely this, the idea
does not violate any known laws.) So with artificial gravity plus an
infinite power source-plus the repeal of Relativity-we could get to any
place in the universe just as quickly as we pleased.

But asking for three miracles is a little greedy; let us stick to one,
and see what would really happen if we could continue a modest 1-g
acceleration indefinitely.

What does happen now depends on the point of view of the observer.  To
the people in the ship, the thrust is constant and their instruments
tell them that they are gaining 80,000 mph every hour.  Everything is
perfectly normal.

But an observer back on Earth, if he could look into the ship would see
that something very strange was happening.  It would be like watching a
film that was slowing down.

When the ship had reached 87 per cent of the speed of light (580
million mph), everything inside it would seem to be taking twice as
long as it should from the point of view of the outside observer; two
hours of ship time would be only one hour of Earth time.  At 98 per
cent of the speed of light the time rate would be slowed fivefold, at
99.5 per cent tenfold, at 99.99 per cent a hundredfold.  Thus the
effect increases very rapidly as one nears the velocity of light; but
once again it must be emphasized that to the crew of the ship, not only
does everything appear normal-everything is normal.  They are not
responsible for the peculiar behavior of the rest of the universe;
their clocks and tape measures are just as good as anybody else's.

Only when they had slowed down, turned around, and come home again
would they discover any discrepancy, and then they would be confronted
with the most famous paradox of the Theory of Relativity.  For
centuries might have passed on Earth, while they had aged only a few
years aboard their speeding ship.

It is not really a paradox, of course; it is the way the universe is
built, and we had better accept it.  (A tiny minority of
mathematicians-Professor

Herbert Dingle is their most vehement spokesman-still refuses to accept
a universe in which this sort of thing can happen.  But the weight of
the evidence is against them.)

In 1522 the Western world was suddenly confronted by a paradox which
must have seemed equally baffling to many-people at the time.  Eighteen
sailors landed at Seville on a Thursday, whereas by their own careful
reckoning it was only Wednesday aboard their ship.  Thus they were,

0 I am fudging some philosophical points here and hope that
relativistic purists will forgive me for describing observations which,
even in principle, cannot be performed.

in their view, a day younger than the friends they had left behind.

They were the survivors of Magellan's crew-the first men to
circumnavigate the world-and they presented the Church with the
frightful problem of deciding just when they should have kept the
various Saints' days on the latter half of their voyage.  Four and a
half centuries later, we have learned to get along with the
International Date Line, though it is going to cause us more and more
trouble with the advent of global television.

Perhaps four and a half centuries from now time dilation will present
no greater intellectual difficulties-though it may certainly cause
grave social ones, when young astronauts return home to greet their
senile great-grandchildren.

The effects that time dilation will produce have been calculated by Dr.
von

Hoerner for various 1-g round trips, with the fascinating results shown
in the table below.  It will be seen how spectacularly the
time-stretching increases with speed; the power consumption and
engineering difficulties, unfortunately, increase even more rapidly. In
the opinion of most scientists, Table 13 begins at a level of mere
absurdity and swiftly mounts to the utterly preposterous; yet it is
(pace Professor Dingle) mathematically sound.

TABLE 13

INTERSTELLAR ROUND TRIPS AT CONSTANT I G

DURATION (OUT AND BACK) "DISTANCE REACHED,

YEARS LIGHT-YEARS

ON BOARD SHIP ON EARTH

1.0 0.06 2 2.10.255 1.7 1: 2: 10 15 so 37 20 270137 25 910455 30
3,1001,560 40 36,00017,500 50 420,000208,000 so 5, 000'0002,470,000

(Adapted from Sebastian von Hoerner, "The General Limits of Space

Travel," in INTERSTELLAR COMMUNICATION, ed.  A. G. W. Cameron, N.Y.,
1963.)

Similar results have been calculated by Dr.  Carl Sagan in a paper with
the forthright and uncompromising title,

"Direct Contact Among Galactic Civilizations by Relativistic
Interstellar Spaceflight," the gist of which will be found in his book
(with 1. S. Shklovskii ) Intelligent Life in the Universe.  Dr.  Sagan
takes these ideas quite seriously and concludes that as far as energy
requirements are concerned, there are no fundamental objections to high
speed (near-ligbt-velocity) travel to the stars.

As a final example of the time-dilation effect, which also gives some
idea of the energy requirements, it would be rather difficult to
surpass a calculation made some years ago by the late Dr.  Eugen
Stinger.  He considered -spaceship circumnavigating the cosmos-assuming
that this represents a distance of ten billion light-years.  If the
ship could achieve 99.999,999,999,999,999,996 per cent of the velocity
of light, the crew would imagine that the journey had lasted
thirty-three years-yet ten billion years would have elapsed before they
returned to Earth (if it still existed, and they could find it).  Since
this feat would require the complete conversion into energy of a mass
approaching that of the Moon,

Stinger decided that this far surpassed the limits of the technically
feasible.

Of course, he may be right.  But because now we know that there are
energy sources in the universe which appear to be turning Moon-sized
masses into radiation every ten seconds, it might be best to reserve
judgment even on this point.

Everything that has been said in this chapter is based on one
assumption, that the Theory of Relativity is correct.  However, we have
seen how

Newton's theory of gravitation, after being unchallenged for three
hundred years, was itself modified by Einstein.  How can we be sure
that this process will not be repeated and that the "light barrier" may
not be shattered, as the once formidable "sound barrier" was a
generation ago?

This analogy is often drawn, but it is quite invalid.  There was never
any doubt that one could travel faster than sound, given sufficient
energy; rifle bullets and artillery.  shells had been doing it for
years.  (In fact, manmade objects first broke the sound barrier at
least 10,000 years ago, though very few people would guess how.  Think
it over before you look at the footnote) 0 The crack of a whip is a
sonic bang.

During the last half century, however, the equations of relativitv have
stood up to every test that can be applied, and billions of dollars'
worth of engineering have been based upon tberyr.  The giant
accelerators that speed atomic particles tip to almost the velocity of
light simply would not work unless Einstein's formulas were obeyed to
as many decimal places as can be measured.

Nevertheless, there is a faint possibility that even this apparently
insuperable barrier may be breached and that we may be able to
signal-conceivably, even travel-faster than light, with all that this
implies.  And we might do it without violating the Theory of
Relativity.

I am indebted to Professor Gerald Feinberg of Columbia University for
these ideas, which are taken (I hope accurately) from his stimulating
paper "On the Possibility of Faster Than Light Particles."  Professor
Feinberg makes a point which is usually overlooked: the Theory of
Relativity does not say that nothing can travel faster than light.  It
says that nothing can travel at the speed of light; there is a big
difference, and it may be an important one.  As Professor Feinberg puts
it..  the speed of light is a limiting velocity, but a limit has two
sides.  One can imagine particles or other entities which can travel
only faster than light; there might even be a whole universe on the
other side of the light barrier, though please do no task me to explain
precisely what is meant by this phrase.

It may be argued that even if this were true, it could never be proved
and would be of no practical importance.  Since we cannot travel at the
speed of light, it seems obvious that we can never travel any faster.

But this is taking an old-fashioned, pre-twentiethcentury view of the
universe.  Modern physics is full of jumps from one condition of energy
or velocity (quantum state) to another without passing through the
intermediate values.  There are electronic devices on the market now
which depend on this effect-the tunnel diode, for example, in which
electrons "tunnel" from one side of an electrical barrier to the other
without going through it.

Maybe we can do the same sort of thing at the velocity of light.

I am well aware that this is metaphysics rather than physics; so are
even more outre ideas like shortcuts through higher dimensions-the
"spacewarps".so useful to science-fiction writers.  But we have been
wrong so many

To The Star$ 0 337

times in the past when attempting to set limits to technology that it
would be well to keep an open mind, even about surpassing the speed of
light.

J. B. S. Haldane once remarked: "The universe is Dot only queerer than
we imagine-it is queerer than we cai imagine."  Certainly no one could
have imagined the time dilation effect; who can guess what strange
roads there' may yet be on which we may travel to the stars?

WHERE'S EVERYBODY?

Any reader who has followed the argument of the last few chapters will
note how skillfully I have managed to paint myself into a corner.  If
it is true that the universe is full of intelligent races and that
physical travel between the stars is possible, why are we still
alone?

This question has been asked many times and has received many answers.
It may well be that the sheer extent of the universe-in time as well as
in space-is sufficient explanation.

Look at Plate 62, which covers only a small portion of the Milky
Way-yet each of the stars in those closely packed fields is separated
from its neighbors by distances of several light-years.  To travel from
one side of the picture to the other, even at the speed of light, would
take centuries; the examination of every star and planetary system
shown here might occupy fleets of spaceships for millennia.  It seems
probable that even if the

Galaxy is full of advanced civilizations, we could not expect our own
Solar

System to be visited except at very rare intervals.

The situation would hardly be affected even if the speed of light were
nota limiting factor.  A man may walk the length of a beach in a few
minutes, but how long would it take him to examine every grain of sand
upon it?  The problem of surveying the universe is of a similar
magnitude, and this is only considering its extension in space.

To look at its duration in time, imagine that the height of the
Empire

State Building represents the age of the 338

Galaxy; on this scale, an inch is about a million years, and each of
the 102 floors represents 150 million years.

The Earth was formed somewhere about the seventieth floor; the first
traces of life appear around the eightieth.  Yet almost all the
familiar evolutionary sequence-the rise and fall of the great reptiles,
the triumph of the mammals, the discovery of tools-takes place on the
very topmost floor.

And man?  His entire history, back to the building of the pyramids,
spans the thickness of the paint on the ceiling of the 102nd floor.

How many civilizations may have arisen, flourished for millions of
years (several inches) on the 102 floors that lie below us, and then
vanished before the onslaught of time?  And how unlikely that there is,
at this moment, even one society in the entire universe poised just
where we are, at the beginning of our atomic age, and dreaming of the
conquest of space!

It is far more probable that any cultures now existing are so many
millions of years ahead of us that our activities would not be of the
slightest interest to them.  We flatter ourselves if we expect
visitors.

But perhaps we are being flattered.  Reluctant though I am to get
involved in the subject, it would be arrant cowardice on my part not to
say something about UFO's, or flying saucers; whether their explanation
is psychological or physical, they constitute one of the most
remarkable phenomena of modern times.  Unfortunately, it has become
extraordinarily difficult to arrive at the truth in this matter; seldom
has any subject been so invested with fraud, hysteria, credulity,
religious mania, incompetence, and most of the other unflattering human
characteristics.

Much of the trouble arises from the fact that the sky presents an
almost endless variety of peculiar sights and objects, only a few of
which are likely to be encountered by one person in a lifetime.  And
when this does happen, he may be misled into thinking that be has seen
something extraordinary-instead of merely unfamiliar.

Let me give an example that may seem a little farfetched but that
illustrates my point perfectly.  Suppose you are completely ignorant of
meteorological phenomena and live in a desert country where it never
rains.

Then one day you step out of doors-to see a huge, semicircular arch
spanning half the sky.  It is so geometrically perfect that it must be
artificial-yet it is obviously miles across and is beautifully colored
in red, orange, yellow, green, blue.... To most of us a rainbow is so
familiar that it no longer causes the least surprise, and unlike our
ancestors, we do not need supernatural explanations for it.  Reason has
told us what it is; there would be many fewer UFO's around today if
reason, or even elementary common sense, were in better supply.

For a long time my own answer to questioners on this agitated subject
was:

"If you've never seen a UFO, you're not very observant.  And if you've
seen as many as I have you won't believe in them."  Over the last
thirty years, in fact, I have encountered at least ten aerial phenomena
that would have fooled almost anybody, and would have left believers in
a state of rapturous euphoria.

In all but one case I was able to dispose of them without difficulty.
The tenth was much more stubborn; several discussions with the Air
Force and some hard work by the Hayden Planetarium computer were needed
to exorcise it.  But it taught me more than all the others; I learned
the hard way that any witness, no matter how skeptical and scientific
be considers himself to be, can misinterpret the evidence of his own
eyes.

The night sky, in particular, is now so crowded with optical
apparitions-meteors, satellites, mirages, met balloons, jet exhausts,
high-flying birds (unbelievably, perhaps the most convincing of
all)-and I no longer take seriously anything I see there myself, still
less anything reported by someone else.  The most genuine of UFO's from
outer space could never be unambiguously identified among all the
visual junk now wanderihg overhead.

What completely killed my interest in nighttime UFO's was the discovery
of this report by a British astronomer, Walter Maunder, published in
the May, 1916, issue of the Royal Astronomical Society's journal The
Observatory, thirty years before the phrase "flying saucer" was
invented.  And Maunder was describing something that be had witnessed
thirty-four years earlier still, in November, 1882, when he was
standing on the roof of the Greenwich

Observatory, looking across London.  Soon after sunset:

A great circular disc of greenish light suddenly appeared low down in
the

East-North-East, as though it had just risen, and moved across the sky,
as smoothly and steadily as the sun, Moon, stars, and planets move, but
nearly a thousand times more quickly.  The circularity of its shape was
merely the effect of foreshortening, for as it moved it lengthened out
.... when it passed just above the Moon its form was almost that of a
very elongated ellipse, and various observers spoke of it as
"cigar-shaped" "like a torpedo" .. . had the incident occurred a third
of a century later, beyond doubt everyone would have selected the same
simile-it would have been "just like a

Zeppelin."

And today, of course, it would be "just like a rocket."

The thing that Maunder and thousands of other witnesses all over Europe
saw on that night was part of a great auroral display.  Of that
explanation there is no possible doubt; the apparently solid object
disintegrated later, its glow was analyzed by the spectroscope and gave
the characteristic auroral lines, and triangulation showed that it was
at least 50 miles long and at an altitude of over 100 miles.  Some
freak of the

Earth's magnetic field had briefly focused beams of solar electrons
into this strange shape.  I find this much more incredible than any
mere visiting spaceship, but the evidence is beyond dispute.

Auroral displays are a form of electrical discharge in the upper
atmosphere, and their theory is now fairly well understood.  This is
not true of the extraordinary phenomenon known as ball lightning, and
in 1959 I suggested that this (or something analogous to it) may be
responsible for some UFO sigbtings.* This theory has recently been
revived, but it can account for only a few cases.

There is evidence that ball lightning is more common at high altitudes
than at sea level, and Professor J. S. Haldane is said to have
encountered it when he was studying low-pressure physiology.  So I once
asked his much more famous son: "Is it true, Professor, that your
father did some work on ball lightning when he was experimenting at the
top of Pike's Peak?"  "No," said

J. B. S."  "ball lightning did some work on my father."  That was all
the information I could get.

But when all possible conceivable and even unlikely explanations are
taken into account, there remains a hard core of UFO sightings in which
either some solid artifact of a very advanced technology has been
observed, or there has been some downright lying and/or massive
hallucinat * See the essay "Things in the Sky," reprinted in The
Challenge of the

Spaceship, which also gives an account of my own UFO sightings up to
1959.

ing.  In most of these cases there can be very little doubt that fraud
or self-delusion is the answer; for a hilarious example, see Carl
Sagan's account of the criminal trial of "Helmut Winckler" (Sliklovskii
and Sagan:

Intelligent Life in the Universe, Chapter 2).  Herr Winckler has
encountered some Saturnians who happened to be speaking Hochdeutsch (as
Saturnians will) and used the information they gave him to extract
money from those ladies of an all-too-certain age who seem peculiarly
addicted to sauceritis.  Yet even in the case of this blatant fraud,
Dr.  Sagan could not decide to what extent

Winckler believed his own concoctions; how much more difficult it is,
therefore, to deal with those reports where apparently sincere and
educated people, who have nothing to gain and a good deal to lose, tell
of their meetings with extraterrestrials.  In many cases there are
obvious psychological explanations which account both for the incidents
themselves and for the avidity with which thousands of frustrated,
worried, or unstable believers accept their truth.

Nevertheless, when all this sad rubbish has been rejected, there still
remains a tiny residue of reports, some of them backed by photographs,
which are very difficult to explain.  This is why many people were
relieved when, in 1966, the United States Air Force called in an
independent scientific team, headed by Dr.  Edward Condon, to
investigate the better-authenticated sightings.  Perhaps this should
have been done a long time ago.

The theory that the "genuine" UFO's are visitors from space, though it
must be taken quite seriously, involves difficulties that make it very
hard to accept.  If this explanation is correct, one would have thought
that it would have been established beyond any doubt, years ago.  The
skies are now scanned night and day by radar and optical networks that
can detect a beach ball as far away as the Moon.  (It is literally true
that some radars can track orbiting nuts and bolts.) Tens of thousands
of amateur astronomers search the heavens for comets and novae, yet it
is rare indeed for these skilled observers to report an unknown.  They
see plenty of strange things, but their scientific background quickly
leads to an identification; they don't go rushing off to the local
paper at the first glimpse of a fuzzy light in the sky.

It would be a rash man who would predict the eventual outcome of the
UFO furor.  Later generations may look upon it much as we now regard
the various religious manias for the Middle

Ages or the "miracles" which even today crop up in backward communities
(vide Fellini's La Dolce Vita).  My own feeling-it is nothing so
definite as a belief-is that the spaceship explanation is a little too
obvious and simpleminded.  It is just possible that UFO's may turn out
to be something really surprising, not merely humdrum visitors from
other planets.

And having already said much more than I intended to, let me make one
other point.  After twenty years of the wretched things, I am bored to
death with

UFO's.  Any letters on the subject will not be forwarded by my
publishers.

If forwarded, they will not be read.  And if read they will not be
answered.

The laws of mathematical probability suggest that for evidence of
extraterrestrials we must look much more deeply into space and time
than at our own age and our own planet.  In addition to the search for
interstellar signals, there are two other possibilities.

First there is the record of the past.  Visitors from space may have
landed on our planet dozens-hundreds-of times during the long, empty
ages while

Man was still a dream of the distant future.  Indeed, they could have
landed on 90 per cent of the Earth as little as two or three hundred
years ago, and we would never have heard of it.  If one searches
through old newspapers, one can find large numbers of curious incidents
that could easily be interpreted as visitations from space.  That
stimulating and eccentric writer Charles Fort made a collection of such
occurrences in his book LO!"  and one is inclined to give them more
weight than any comparable modern reports, for the simple reason that
they long predate current interest in space travel.

Going further back in time, it has been suggested that some of the
legends and myths of prehistory, perhaps even the weird entities of
many religions-look at the marvelous pantheon of Hindu gods-may have
been inspired by glimpses of beings from other worlds.  Sbklovskii and
Sagan give several striking examples in Intelligent Life in the
Universe and reproduce some Babylonian seals that are, to say the
least, stimulating materiel for such discussions.

Unfortunately, indirect evidence can never be conclusive; the
myth-making abilities of the human mind appear to be virtually
limitless.  Only some artifact-a derelict spaceship, a fossilized
radio-would be good enough to establish a case; and even then it might
be difficult to eliminate the possibility that some advanced
terrestrial culture was not responsible, though of course this would be
almost as exciting and important.

The chances of such a discovery on this planet are remote indeed.
Weather, war, the ravages of time-these would combine to destroy all
but the most adamant of relics.  Anything made of metal would certainly
be broken up for tools or weapons; perhaps the only hope of such a find
lies in the vast new realm of underwater archaeology.  What secrets may
be lying in the seas that cover two thirds of the world!  Were it not
for the Antikythera wreck salvaged in 1900, we should never have known
that the Greeks had constructed highly sophisticated astronomical
computers in the first century B.C.* On land the valuable bronze of
this mechanism would have been melted down and reshaped over and over
again during the last two thousand years.  The ocean bed is a time
capsule whose treasures we have only just begun to recover.

The Moon and planets, when we reach them, may provide even better
opportunities.  On airless satellites, particularly in caves protected
from meteoric bombardment, even the most fragile objects would be
preserved unchanged for millions of years.  The abandoned debris of
interstellar expeditions, perhaps even scientific instruments
deliberately left behind to monitor and report the progress of events
in the Solar System-these are some of the things we may find when our
own explorations begin.  Remember the shock that Robinson Crusoe
received when he walked along his lonely beach.  We may yet discover
that ours are not the first footprints on the

Moon.

In the long run, the prospect of meeting other forms of intelligence is
perhaps the most exciting of all the possibilities revealed by
astronautics.  Whether or not man is alone in the universe is one of
the supreme questions of philosophy.  It is difficult to imagine that
anyone could fail to be interested in knowing the answer-and only
through space travel can we be sure of obtaining it.

0 See D. J. de S. Price, "An Ancient Greek Computer," Sczentific
American,

June, 1959.

We have seen that there is little likelihood of encountering
intelligence elsewhere in the Solar System.  That contact may have to
wait for the day, perhaps ages hence, when we can reach the stars.  But
sooner or later it must come.

There have been many portrayals in literature of these fateful
meetings.

Most science-fiction writers, with sad lack of imagination, have used
them as an excuse for stories of conflict and violence
indistinguishable from those which stain the pages of our own history.
Such an attitude shows a complete misunderstanding of the factors
involved.

It has already been pointed out that ours must be one of the youngest
cultures in the universe.  If ships from Earth ever set out to conquer
other worlds, they may find themselves, at the end of their journeys,
in the position of painted war canoes drawing slowly into New York
harbor.

What, then, if we ever encounter races which are scientifically
advanced yet malevolent-the stock villains, in fact, of that type of
fiction neatly categorized as "space opera"?  In that event,
astronautics might well open a Pandora's Box which could destroy
humanity.

This prospect, though it cannot be ruled out, appears highly
improbable.  It seems unlikely that any culture can advance, for more
than a few centuries at a time, on a technological front alone.  Morals
and ethics must not lag behind science; otherwise (as our own recent
history has shown) the social system will breed poisons which will
cause its certain destruction.  With superhuman knowledge there must go
equally great compassion and tolerance.

When we meet our superiors among the stars, we need have nothing to
fear save our own shortcomings.  just how great these are is something
we seldom stop to consider.  Our impressions of reality are determined,
far more than we imagine, by the senses through which we make contact
with the external world.  How utterly different our philosophies would
have been had Nature economized with us, as she has done with other
creatures, and given us eyes incapable of seeing the stars.  Yet how
pitiably limited are the eyes we do possess, turned as they are to but
a single octave in the spectrum.  The world in which we live is
drenched with invisible radiations, from the radio waves which we have
so recently discovered coming from Sun and stars to the cosmic rays
whose origin is still one of the prime mysteries of modern physics.
These things we have discovered within the last generation, and we
cannot guess what still lies beneath the threshold of the senses, ho
ugh recent discoveries in paranormal psychology hint that the search
may be only beginning.

The races of other worlds will have senses and philosophies very
different from our own.  To recall Plato's famous analogy, we are
prisoners in a cave, gathering our impressions of the outside world
from shadows thrown upon the walls.  We may never escape to reach that
outer reality, but one day we may hope to reach other prisoners in
adjoining caves, where we may learn far more than we could ever do by
our own unaided efforts.

Somewhere on that journey we may at last learn what purpose, if any,
life plays in the universe of matter; certainly we can never learn it
on this

Earth alone.  Among the stars lies the proper study of mankind; Pope's
aphorism gave only part of the truth, for the proper study of mankind
is not merely Man, but Intelligence.

CONCERNING MEANS AND ENDS

Ah who shall soothe these feverish children?  Who justify these
restless explorations?

WALT WHITMAN-Passage to India

Having ranged, in imagination at least, throughout the universe, let us
now come back to Earth for final summing-up of the position of
astronautics today.  Hitherto we have been concerned with purely
scientific questions; now it is time to take the wider view.

Even its most enthusiastic supporters do not deny that the exploration
of the Solar System is going to be a very difficult, dangerous, and
expensive task.  The difficulties must not, however, be exaggerated,
for the steadily rising tide of technical knowledge has a way of
obiterating obstacles so efFectively that what seemed impossible to one
generation becomes elementary to the next.  Once again the history of
aeronautics provides a useful parallel.  If the Wright brothers had
ever sat down and considered just what would be needed to run a world
air-transport system, they would have been appalled at the total
requirements, despite the fact that these could not have included all
the radio and radar aids which were undreamed of sixty years ago.  Yet
all these tbiDgs, and the vast new industries and the armies of
technicians that lie behind them, have now become so much a part of our
lives that we scarcely ever realize their presence.

The enterprise and skill and resolution that have made our modern world
will be sufficient to achieve all that has been described in this book,
as well as much that still lies 347

beyond the reach of any imagination today.  Given a sufficiently
powerful motive, there seems no limit to what the human race can do;
history is full of examples, from the pyramids to the Manhattan
"Project, of achievements whose difficulty and magnitude were so great
that very few people would have considered them possible.

The important factor is, of course, the motive.  The pyramids were
built through the power of religion, the Manhattan Project under the
pressure of war.  What will be the motives which will drive men out
into space and send them to worlds most of which are so fiercely
hostile to human life?

So far, those motives have been largely political-or
ideological-arising from conditions which one hopes will not be
permanent.  Spacefaring, if it is to continue, needs a more stable
basis than national pride.

The suggestion has sometimes been made that the increasing pressure of
population may also bring about the conquest of the planets.  There
might be something in this argument if the other planets could be
colonized as they stand, but we have seen that the reverse is the case.
For a long time to come, it is obvious that, if sheer lebensraum is
what is needed, it would be much simpler and more profitable to exploit
the undeveloped regions of this Earth.  It would be far easier to make
the Antarctic bloom like the rose than to establish large,
self-supporting colonies on such worlds as

Mars, Ganymede, or Titan.  Yet one day, the waste places of our world
will be brought to life, and when this happens, astronautics will have
played a major role in the achievement through the orbital weather
stations and, perhaps, direct climatic control by the use of orbiting
space mirrors.  When this has happened-indeed, long before-men will be
looking hungrily at the planets, and their large-scale development will
have begun.

Whether the population of the rest of the Solar System becomes 10
million or 10,000 million is not, fundamentally, what is important.
There are already far too many people on this planet, by whatever
standards one judges the matter.  It would be no cause for boasting if,
after some centuries of prodigious technical achievement, we enable ten
times the present human population to exist on a dozen worlds.

Only little minds are impressed by size and number.  The importance of
planetary colonization will lie in the variety and diversity of
cultures which it will make possible-cultures as different in some
respects as those of the Eskimo and the Pacific islanders.

They will, of course, have one thing in common, for they will all be
based on a very advanced technology.  Yet, though the interior of a
colony on Pluto might be just like that of one on Mercury, the
different external environments would inevitably shape the minds and
outlooks of the inhabitants.  It will be fascinating to see what
effects this will have on human character, thought, and artistic
creativeness.

These things are the great imponderables of astronautics; in the long
run they may be of far more importance than its purely material
benefits, considerable though these will undoubtedly be.  This has
proved true in the past with many great scientific achievements.
Copernican astronomy,

Darwin's theory of evolution, Freudian psychology-the effect of these
on human thought far outweighed their immediate practical results.

We may expect the same of astronautics.  With the expansion of the
world's mental horizons may come one of -the greatest outbursts of
creative activity ever known.  The parallel with the Renaissance, with
its great flowering of the arts and sciences, is very suggestive.  "In
human records," wrote the anthropologist J. D. Unwin, "there is no
trace of any display of productive energy which has not been preceded
by a display of expansive energy.  Although the two kinds of energy
must be carefully distinguished, in the past they have been ... united
in the sense that one has developed out of the other."  Unwin continues
with this quotation from Sir James

Frazer: "Intellectual progress, which reveals itself in the growth of
art and science ... receives an immense impetus from conquest and
empire."

Interplanetary travel is now the only form of "conquest and empire"
compatible with civilization.

It has often been said-and though it is becoming platitudinous, it is
nonetheless true-that only through space flight can mankind find a
permanent outlet for its aggressive and pioneering instincts.  The
desire to reach the planets is only an extension of the desire to see
what is over the next hill, or

Beyond that last blue nwuntain barred with snow Across that angry or
that glittering sea.

Perhaps one day men will no longer be interested in the unknown, no
longer tantalized by mystery.  This is possible, but when man loses his
curiosity, one feels he will have lost most of the other things that
make him human.

The long literary tradition of the space-travel story shows how deeply
this idea is rooted in man's nature; even if nota single good
"scientific" reason existed for going to the planets, he would still
want to go there, just the same.

In fact, as we have seen, the advent of space travel will produce an
expansion of scientific knowledge perhaps unparalleled in history. Now,
there are a good many people who think that we have already learned
more than enough about the universe in which we live.  There are others
(including perhaps most scientists) who adopt the noncommittal
viewpoint that knowledge is neither good nor bad and that these
adjectives are only applicable to its uses.

Yet, knowledge surely is always desirable, and in that sense good; only
insufficient knowledge or ignorance can be bad.  And worst of all is to
be ignorant of one's ignorance.  We all know the narrow, limited type
of mind which is interested in nothing beyond its town or village and
bases its judgments on these parochial standards.  We are
slowly-perhaps too slowly-evolving from that mentality toward a world
outlook.  Few things will do more to accelerate that evolution than the
conquest of space.  It is not easy to see how the more extreme forms of
nationalism can long survive when men have seen the Earth as a pale
crescent dwindling against the stars, until at last they look for it in
vain.

Although man has occupied the greater part of the habitable globe for
thousands of years, until only five centuries ago he
lived-psychologically-not in one world but in many.  Each of the great
cultures in the belt from Britain to Japan was insulated from its
neighbors by geography or deliberate choice; each was convinced that it
alone represented the flower of civilization and that all else was
barbarism.

The "unification of the world," to use Toynbee's somewhat optimistic
phrase, became possible only when the sailing ship and the arts of
navigation were developed sufficiently to replace the difficult
overland routes by the easier sea passages.  The result was the great
age of exploration, whose physical climax was the discovery of the
Americas and whose supreme intellectual achievement was the liberation
of the human spirit.  Perhaps no better symbol of the questing mind
of

Renaissance man could be found than the lonely ship sailing steadfastly
toward new horizons, until east and west had merged at last and the
circumnavigation of the globe had been achieved.

First by land then by sea, man grew to know his planet; but its final
conquest was to lie in a third element, and by means beyond the
imagination of almost all men who had ever lived before the twentieth
century.  The swiftness with which mankind has lifted its commerce and
its wars into the air has surpassed the wildest dreams.  Through this
mastery the last unknown lands have been opened up; over the road along
which Alexander burnt out his life, the businessmen and civil servants
now pass in comfort in a matter of hours.

The victory has been complete, yet in the winning it has turned to
ashes.

Every age but ours has had its El Dorado, its Happy Isles, or its
Northwest

Passage to lure the adventurous into the unknown.  A lifetime ago men
could still dream of what might lie at the poles, but now the North
Pole is the crossroads of the world.  We may try to console ourselves
with the thought that even if Earth has no new horizons, there are no
bounds to the endless frontier of science.  Yet it may be doubted if
this is enough, for only very sophisticated minds are satisfied with
purely intellectual adventures.

The importance of exploration does not lie merely in the opportunities
it gives to the adolescent (but not-to-be despised desires for
excitement and variety.  It is no mere accident that the age of
Columbus was also the age of Leonardo, or that Sir Walter Raleigh was a
contemporary of Shakespeare and Galileo.  Some of these men combined in
themselves the "productive and expansive energies" of which Unwin
spoke.  But today all possibility of expansion on Earth itself has
practically ceased.

The thought is a somber one.  Even if it survives the hazards of war,
our culture is proceeding under a momentum which must be exhausted in
the foreseeable future.  Fabre once described how he linked the two
ends of a chain of marching caterpillars so that they circled endlessly
in a closed loop.  Even if we avoid all other disasters, this could
typify humanity's eventual fate when the impetus of the last few
centuries has reached its peak and died away.  For a closed culture,
though it may endure for centuries, is inherently unstable.  It may
decay quietly and crumble into ruin, or it may be disrupted violently
by internal conflicts.  Space travel is a necessary, though not in
itself a sufficient, way of escape from this predicament.

It is now 400 years since Copernicus destroyed medieval cosmology and
dethroned the Earth from the center of creation.  Shattering though the
repercussions of that fall were in the fields of science and
philosophy, they scarcely touched the ordinary man..  To him this
planet is still the whole of the universe; he knows that other worlds
exist, but the knowledge does not affect his life and therefore has
little real meaning to him.

All this will be changed before the next century is far advanced.  Into
a few decades may be compressed more profound alterations in our world
picture than occurred during the whole of the Renaissance and the age
of discovery that followed.  To our children the Moon may become what
the Americas were 400 years ago-a world of unknown danger, promise, and
opportunity.  No longer will Mars and Venus be merely the names of
wandering lights seldom glimpsed by the dwellers in cities.  They will
be more familiar than ever they were to those eastern watchers who
first marked their movements, for they will be the new frontiers of the
human mind.

Those new frontiers are urgently needed.  The crossing of space-even
though only a handful of men take part in it-may do much to reduce the
tensions of our age by turning men's minds outward and away from their
tribal conflicts.  It may well be that only acquiring this new sense of
boundless frontiers will the world break free from the ancient cycle of
war and peace.

No doubt there are many who, while agreeing that these things are
possible, will shrink from them in horror, hoping that they will never
come to pass.  They remember Pascal's terror of the silent spaces
between the stars and are overwhelmed by the nightmare immensities
which Victorian astronomers were so fond of evoking.  Such an outlook
is somewhat naive, for the meaningless millions of miles between the
Sun and its outermost planets are no more, and no less, impressive than
the vertiginous gulf lying between the electron and the atomic
nucleus.

Mere distance is nothing; only the time that is needed to span it has
any meaning.  Our spacecraft now reach the Moon in

14.

less time than a stagecoach once took to travel the length of England.
When the atomic drive is reasonably efficient, the nearer planets would
be only a few weeks from Earth, and so will seem scarcely more remote
than are the antipodes today.

It is fascinating, however premature, to try to imagine the pattern of
events when the Solar System is opened up to mankind.  In the footsteps
of the first explorers will follow the scientists and engineers,
shaping strange environments with technologies as yet unborn.  Later
will come the colonists, laying the foundations of cultures which in
time may surpass those of the mother world.  The torch of civilization
has dropped from failing fingers too often before for us to imagine
that it will never be handed on again.

We must not let our pride in our achievements blind us to the lessons
of history.  Over the first cities of mankind, the desert sands now lie
centuries deep.  Could the builders of Ur and Babylon-once the wonders
of the world have pictured London or New York?  Nor can we imagine the
citadels that our descendants may one day build beneath the blistering
sun of

Mercury or under the stars of the cold Plutonian wastes.  And beyond
the planets, though ages still ahead of us in time, lies the unknown
and infinite promise of the stellar universe.

There will, it is true, be danger in space, as there has always been on
the oceans or in the air.  Some of these dangers we may guess; others
we shall not know until we meet them.  Nature is no friend of man's,
and the most that be can hope for is her neutrality.  But if he meets
destruction, it will be at his own hands and according to a familiar
pattern.

The dream of flight was one of the noblest and one of the most
disinterested of all man's aspirations.  Yet it led in the end to that
B-29 driving in passionless beauty through August skies toward the city
whose name it was to seal into the conscience of the world.  Already
there has been half-serious talk concerning the use of the Moon for
military bases and launching sites.  The crossing of space may thus
bring, nota new

Renaissance, but the final catastrophe that haunts our generation.

That is the danger, the dark thundercloud that threatens the promise of
the dawn.  The rocket has already been the instrument of evil, and may
be so again.  But there is no way back into the past; the choice, as
Wells once said, is the universe-or nothing.  Though men and
civilizations may yearn for rest, for the dream of the lotus-eaters,
that is a desire that merges imperceptibly into death.  The challenge
of the great spaces between the worlds is a stupendous one; but if we
fail to meet it, the story of our race will be drawing to its close.
Humanity will have turned its back upon the still untrodden heights and
will be descending the long slope that stretches, across a thousand
million years of time, down to the shores of the primeval sea.

BIBLIOGRAPHY

The literature of astronautics is now enormous, and only a few of the
most recent or most readily available works are listed here.

The standard history and general introduction is Willy Ley's Rockets,

Missiles, and Space Travel (New York: Viking, 1961).  Also
authoritative and lavishly illustrated is History of Rocketry and Space
Travel, by Wernher von Braun and Frederick 1. Ordway (New York:
Crowell, 1967).  The Coming of the Space Age, edited by Arthur C.
Clarke (Des Moines: Meredith, 1967), contains a good deal of historical
material, along with autobiographies of

Tsiolkovsky, Goddard, and Obertb.

The annual NASA volumes, Astronautics and Aeronautics, are a valuable
listing of each year's activities in space.  The NASA Historical Series
(Washington, D.C.: Government Printing Office) will provide a detailed
record of the United States space program as it proceeds.  See, for
example,

This New Ocean: A History of Project Mercury, by Loyd S. Swenson, James
M. Crimwood, and Charles C. Alexander (1966).

On the popular level are Careers in Astronautics and Rocketry, by
Carsbic

C. Adams, Wernher von Braun, and Frederick I. Ordway (New York:

McGraw-Hill, 1962); Man and Space, by Arthur C. Clarke (New York:

LIFE

Science Library, 1964); Beyond the Solar System, by Willy Ley and
Chesley

Bonestell (New York: Viking, 1964); We Are Not Alone, by Walter
Sullivan (New York: McGraw-Hill, 1964).

More technical but entirely understandable to the nonspecialist and
great fun to read is Intelligent Life in the Universe, by 1. S.
Shklovskii and

Carl Sagan (San Francisco: Holden-Day, 1966).  Easily understood by
anyone with high-school mathematics is the stimulating Thrust into
Space, by

Maxwell NA'.  Hunter (New York; Holt, Rinehart and Winston, 1965). This
is one of a series of excellent, authoritative, and inexpensive books
on astronautics in the Holt Library of Science.  Other titles are
Manned Space Flight, by Max Faget; A History of Space Flight, by

Eugene M. Emme (the NASA historian) and Communications in Space, by
Leonard

Jaffe (all four published in 1965).  A specialized and quite technical
but very useful book is Interstellar Communication, edited by A. G. W.
Cameron (New York: W. A. Benjamin, 1963).  Perhans the most valuable
single reference book for the serious student is Samuel Glasstone's
Sourcebook of the Space

Sciences (Princeton: Van Nostrand, 1965), which contains in compact
form all the basic scientific information about astronautics and
astronomy.

To keep in touch with current activities in more detail than is
reported by the press, the various suecialized periodicals are
essential.  These include

Aviation Week, Aerospace Technology (formerly Missiles and Rockets),
and

Space World.  Sky and Telescope, though astronomically oriented,
contains a great deal of material on space.  In the United Kingdom the
magazine

Spaceflight is published by the British Interplanetary Society (12,

Bessborough Gardens, London, S.W. 1).

INDEX

ABM's, 83 return, 213

Accelerationspecifications, 189-194 and Galileo, 65 takeoff, 199-201
tolerable, 144, 332 timetable for, 212-213

Accelerometers, 56 vehicle, 136, 150, 153,

Aerobee rocket, 89, 163 188-194

Aerospace plane, 238, 283 Applications Technology

Agena, 182Satellites, 117, 148, 156

Air resistance, 60-63 Ariel 1, 107

Alcohol as rocket fuel, 53 Arizona meteor crater, 225

Allen, H. J."  143 Ark, interstellar, 328-329

Alouette, 107, 110 Asimov, Dr.  Isaac, 296

Alpha Centauri, 312 Asteroids near Jupiter, 145,

Alphonsus crater, 167 261

Altair, 320 orbits of, 273

American Astronautical Astronauts

Association, 37 chores of, 110, 139

American Institute of Aeronau- food and water for, 141 tics and
Astronautics, 37 and meteoroids, 145

American Rocket Society, 103 oxygen for, 140-141

American Telephone and and radiation, 146

Telegraph Company, 124 and Tsiolkovsky, 31

Ames Aeronautical in vacuum, 144-145

Laboratory, 143 and weightlessness, 66,

Ammonia 134-135, 137 and planets, 274, 276, 278 Astronomy as
propellant, 51 radio, 109-110

Andromeda Nebula, 305, 308, X-ray, 228 314 Atlantic Monthly, 25

Aniline as propellant, 51 Atlas missile, 57, 91, 93

Anna I-B, 104Atlas vehicle, 124, 140, 188

Anti-ballistic-missile missile Atmosphere (ABM), 83 of Earth, 60-64

Antigravity, 28, 288-289 on Moon, 215, 216

Apollo Logistic Support of outer planets, 274,

System (ALSS), 222 276-277

Apollo mission, 184 in space vehicles, 141, 146 danger from Sun,
146-147 ATS I communications disaster, 140 satellite, 114-115,"8
docking maneuver, 204 205 Atterley, J."  28

Earth orbit, 201 Aurora and UFO, 341 food and water for, 141 Automatic
Picture landing on Moon, 203 Transmission, 117

Balloons Ceres, 273 invented, 23Chinese and rockets, 48 as
observatories on Jupiter, Circle as orbit, 75 302 Clark University, 33,
37 as rocket boosters, 62 Cocconi, Giuseppe, 321

Balloon satellites, 101, 104, Colony 123,124 lunar,233-Z38

Baltimore, 24, 94 Martian, 294

Barnard's star, 310 planetary, 349

Barringer Crater, 225 Comets, 74,262

Begum's Fortune, The, 27 Command Module (CM),

Beings, extraterrestrial, 22, 188,193,199,202,204 342-346 205,211,212

Bell Laboratories, 124 Communication

Bergerac, Cyrano de, 22, 290 with stars, 319-325

Bernal, Professor J. D."  328; and undeveloped countries, quoted, 10
131

Beyond the Planet Earth, 32 Communications Satellite

Bickerton, Professor, 84-85 Corporation, 128

Biology Communications satellites and climate of Venus, 295 (Comsats)',
122,128-132, and space laboratory, ~28 n."  131 n. 154-155 Computers

Bombs, thermonuclear, 91 and celestial mechanics, 70

Booster, reusable, 237-238, Greek, 344 283 and mid-course
corrections,

Braking and re-entry, 61, 140 168

Brick Moon, The, 25-27 Comte, Auguste, 318

Bricks and thought ex peri- Condon, Dr.  Edward, 342 ment, 42, 44, 77,
79, 80 Congreve, Colonel William, 48

British Interplanetary Society Cooling, regenerative, 53

"Artificial Satellite" Copernicus crater, 177, congress, 91 178-179 see
also Journal of the BIS.  Cosmos satellites, 121, 121 n.

Broadcasting, radio, and Courier, 123

Comsats, 128-131 Crater gravitational, 68, 71-73,

California Institute of 161, 232, 244, 245-247

Technology, 37 n. meteoric, 225

Canada, 107, 110 Craters, on Moon, 32, 124,

Cancer research and space 168,177, 178-179, 217, program, 155 218

Cape Kennedy, 98, 128 n."  Crawler, the, 198 171,197Cultures, closed,
349-352

Celestial mechanics, 70, 101, 254 Dallas Symposium on the

Centaur-Atlas vehicle, 171 Commercial Uses of Space,

Ceramics for spacecraft, 25 156

Data-collection satellites, ESSA satellite, 114-115, 117, 119-120 148

Deep Space Network, 176 Exhaust speed of rocket, 77-81

Dingle, Professor Herbert, Exploration and expansion of 333 knowledge,
350

Discourse Concerning a New Exploration of Space, The, 11,

World, A, 2212, 14; quoted, 183

Discoverer satellites, 120 Exploration of the Moon, The,

Dog, Soviet, 94, 100, 135 13

Doppler effect, 113 Explorer 1, 95, 105

Domberger, General Walter, Explosions, nuclear, and 52, 84 n.
satellites, 120, 121

Drake, Dr.  Frank, 3Z4 Extraterrestrials, 22, 342-346

Draper, Dr.  Charles Stark, 147 Faraday, Michael, 112

Dyson, Dr.  Freeman, 323 Feinberg, Professor Gerald, Early Bird
communications First Men in the Moon, The, satellite, 14, 119, 129-130
27,288 orbit of, 75Flares, solar, 109, 147

Earth Florida and Jules Verne, 24 atmosphere of, 62, 297 Flourine, 51,
279, 2&Z escaping from, 67-68, 72, "My-by," 249 76-77, 82-83 Mars, 255,
257-258 mass of, 42 Venus, 254, 257-258 orbits of satellites, 94-101
Flying saucers, 339-342 origins of life on, 297 Fontenelle, Bernard de,
22 shape of, 100, 104-105 Food, for astronauts, 141

Eccentricity of artificial for lunar colony, 234 satellite, 96Force,
centrifugal, 31, 32, 37

Echo,14,101,104,123,124 Fort, Charles, 343

Edison, Thomas A."  30 Friedman, Dr.  Herbert, 228

Edwards, J. H.2 56 From the Earth to the Moon,

Eisenhower, President 23,24

Dwight D."  121 Frontiers, space travel and

Einstein, Albert, 42 new,353

General Theory of Rela- Fuel tivity, 64, 135, 331, 333, nuclear
reactions, 284-287 336 see also Propellants

Energy and escape from Earth, Gagarin, Yuri, 14, 136, 140, 66-68 143
and velocity, 71 Galaxies, other, 316

Engines, of Saturn 5,189Galaxy 194,199age of our, 323, 338-339

Escape law, 67-69 defined,305 see also Crater, gravitational extent of,
306-316

Escher, William, 237 n. Galileo, 20, 65, 275

GeminiHayden Planetarium, 116, 340 astronauts, 110, 120, 139, H-bomb,
285 182Heat and spacecraft, 141-144 missions, 136,140,141 Heat shield,
140,144

General Theory of Relativity, Hilton, Barron, 156 64,135,331,333
Hitler, Adolf, 56 and Feinberg, 336 Hohmann, Dr.  Walter, 248

Geodesy, 104 Hotel, orbital, 156

Geos 1, 104Houbolt, Dr.  John C."  185 n.

Gilbert, G. K."  225 Hoyle, Dr.  Fred, 277

Hughes Aircraft Company,

Glenn, John, 14,259 119,125,171 and Project Mercury, 136, Humphrey,
Vice President 144 Hubert, 128 n.

Goddard, Esther, 35, 36, 44 n. Humanity and interstellar

Goddard, Robert Hutchings, travel, 329 32-37, 85, 133 Hunter, Maxwell,
286 and rocket propulsion, 43-44 Huntsville, Alabama, 92

Goddard Space Flight Center, Hydrogen, liquid, 51, 57, 189
37,104Hydrogen atoms and inters tel

Godwin, Bishop, 21-22 Far signals, 321

Gravity Hydrogen peroxide, 55 and acceleration, 144 Hyginus Ri IIe 227
and astronauts, 134-135 Ikeya-Seki comet, 262 and leaving Earth, 60,
64-69 Indians and rocket, 48 on Jupiter, 66 Industry on Moon, 65 on
Moon, 237 for space station, 149 orbital, 156

"Gravity insulators", M Institute for Advanced

Greeks Studies, 323 computer of, 344 Intelligence, other forms of, and
come sections, 75 345-346

Grissom, Virgil, 136 Intelligent Life in the

Ground track of satellites, 98 Universe, 335, 341, 343

Guggenheim Fund for the Pro- Intelstat communications motion of
Aeronautics, satellite, 129,132 ,34,36International Date Line, 334

Guidance, inertial, 55-56 International Geophysical

Year (IGY), 91

Hadrian, 292Interplanetary Flight, 11, 14

Haldane, Professor J. B. S."  Ionosphere, 62, 63, 107
155,337,341Italians and space flight, 96 jet Propulsion Laboratory,
12,

Haldane, Professor J. S."  341 171,255

Hale, Edward Everett, 24, 25, Ranger spacecraft, 165, 27,"3 167,168

Hall, Dr.  Asaph, 27 Jodrell Bank, 169

Index e 361

Journal of the British Inter" Light barrier," breaching, planetary
Society, 12, 56, 336 183, 237 n.Light-year, defined, 306

Jupiter, 242, 246 Lindbergh, Charles A."  34 atmosphere, 274 exploring,
296Lockheed Missile and Space and Galileo, 20-21 Company, 286 gravity
on, 66, 298-299, 300 Lowell Observatory, 277 life on, 298-299 "Lox,"
50, 51, 189 radio emissions from, 275 Lucian of Samosata, 20 satellites
of, 275 Luna 1 ("Mechta"), 163, 253 space probe to, 258-259 Luna 2, 85,
162, 163, 164 temperature, 297 Luna 3, 32,164

Jupiter missile, 91 Luna (5,6,7,8), 169

Kaplan, Dr.  Joseph, 91 Luna 9, 170

Kardashev, N. S."  323 Luna 10, 170,176

Kennedy, President John F."  Luna 13,180 183-184 Cunar Module (LM),
188,

Kepler, Johannes, 21, 75 201-202,203, 210 third law, 73Lunar Orbiters,
120, 171-177

Kerosene, 50, 51, 57, 191 model, 175

Kopal, Professor, 153 photos from, 33, 124, 173,

Laboratory, universe, 154, 155 176,177, 178-179, 227,

Laika, 94, 100, 135 229

Lalande 21185, 310

Langley Research Center, Lunar Orbit Rendezvous, 185 185 n. Lunatron,
237 n.

Laser beams and geodesy, 104 and interstellar signals, 320 Making of a
Moon, The, 13;

Launch quoted, 122 speeds,76-77Man and space flight, 133-147 vehicles
and space stations, Man in the Moone, 21 150 Manned Orbiting Laboratory
window, 199

Lawrence, T. E."  30 (MOL), 149

Leonard, Jonathan, 329 Manned Orbiting Research

Ley, Willy, 38, 39, 123 Laboratory (MORL),

Libration points, 231 149

Life Mare Imbrium, 85,164 adaptability of, 279 Mare Orientale, 217 on
Earth, origins of, 297 Mariner 4, 12, 255, 257, 258, human, and
interstellar travel, 328-331 269

Light photos by, 269,272 exceeding speed of, 337 Mariner spacecraft,
255, reaching speed of, 327, Z55 n."  264 n. 332,333 predicted, 11,
12

Mars, Z42,246Missiles (Continued) colonies on, 294-295 ICBM, 121,143
fly-by, Z55, 257, 258, 269 Redstone, 40,91,92,94 gravity on, 60,
266-267 V-2,52-59 journey to, 248, 252, 256 MIT.  Instrumentation LIFE
on, 267, 268-269 Laboratory, 147 maria, 266 Moby Dick, 25 photos of,
255-256, 258, 269 Molmya satellites, 129 satellites of, 27, 268-269
Moon surface, 265-268 Alphonsus crater, 167-168 transportation on, 294
Apollo Mission to, 187-213

Marshall Space Flight Center, as base for experiments, 189 228,231

Martin Company, 24,94 and Bishop Wilkins, 22

Mass ratio and propellants, colony on, 233-238 78-84 Copernicus crater,
177,

Mathematicians and come 178-179 sections, 75early flights to, 14,
163-180

Mechta, 163, Z53,254 enviromnent on, 214-216

Mercury, 214, 242, Z46 escaping from, 68-69,74, orbit, 27 1, V 2 236
temperature, 292 exploring, 219-225, 227

Mercury flights, 93 Farside, 164, 169, 176, 218 astronauts, 110 first
landings, 164-167, 168 capsule, 136, 140 170, 171-180 heat shield, 143,
144 as fueling stop, 236

Metoor, 107 and Goddard, 34

Meteorite, 107, 143 gravitational crater of, 60,

Meteoroids, frequency of, 65,68-69,71-73,161 107,145 162,231,241

Methane, 296 Hyginus Rille, 227 and planets, 274, 276, 278 imaginary
trips to, 19-29

Vicroinegas, 22-23 life on, 219, 233-235

Midas satellites, 121 photographs of, 164, 165,

Milky Way, 306,307,311, 168-172,180 314,316 second, 231 civilizations
in, 323, 338, and Soviets, 94 345 spacecraft for voyage to,

Maunder, Walter, 340-341 182-183,184-185

Miller, Representative George, surface of, 170, 172, 173, 198
180,215,216-218,223

Miller, Stanley, 297 228,236

Minuteman missile, 48 temperature, 222

Mirrors, space trajectory to, 161-162 and geodesy, 104 Tsiolkovsky
crater, 33, 218 and Oberth, 38Tycho crater, 124

Missiles, anti-ballistic-missile Vitello crater, 227 (ABM), 83 water
on, 233, 235

Atlas, 57, 91, 93 see also Luna and Sputnik

Moons Orbits (Continued) of Mars, 268-269 Hohmann, 248, 252, 255 of
Saturn, 276-277 retrograde, 97

Morrison, Philip, 321 Oxygen

Mount Palomar telescope, and atmosphere of space 230,316 craft, 141

National Academy of Science, and evolution, 298 11 liquid, 50, 51,
189

National Aerospace Museum, for space transporter, 283 35 Ozone,63

National Rocket Club, 44

National Science Foundation, Pageos satellite, 104-105 103 Parabola,
75

Nature, 319, 321 Paris Air Show, 90,92

Navaho missile, 91 Payload and mass ratio, 80-84

NavigationPeenerminde, 52, 84 n. and bouncing off planets, rocket
engineers of, 39, 89, 259,289 90,93,94-95 and the.  Brick Moon, 25
Pegasus satellites, 107 and satellites, 120-121 Photographs

Navsat network, 116 of Farside of the Moon,

Neptune, 242, 246, 274, 277 164,169,177 voyageto,289lunar telescopic,
214-215

Newton, Sir Isaac, 44, 64, 66 of Mars, 256

New York Times, 44 of Moon, 164, 167, 168-170,

Nicolson, Marjorie Hope, 29 177, 178,179,180

Nimbus satellite, 117, 148 Pierce, Dr.  John R."  124

Nininger, H. H."  143 Pioneer probes, 163

Nordhausen, 57 Planets

Novae, 313ancient knowledge of, 19-20 bouncing rockets from, 259,

Oberth, Hermann, 32, 133 289 theories, 37-40,120, 122challenge of
developing, 123 292-302

Office of Naval Research, 94 density of, 260

Orbital Workshop, 149 first artificial, 163

Orbiter vehicles, 120, 218 gravitational fields of, 245 Orbiting
Astronomical Obser- Hohmann orbits to, 248, va tory (OAO), 109, 110
252,255

Orbiting Geophysical Labora- periods of, 244 tory (OGO), 106
temperatures, 292, 294.  295

Orbiting Solar Observatory Plants (OSO),109 on Mars, 266-268

Orbits on Moon, 234-235 of artificial satellites, 94-101Plurality of
Worlds, A, 22 elliptical, 73-75 Pluto, 242, 244, 246, 277-278 near
Earth, 70,72,74,75, journey to, 277 77,99-101 temperature on, 293

Plutonium, and atomic rockets, Re-entry

Z86, 287of Apollo mission, 210

Polaris missile, 48 and atmosphere, 61, 140,

Precession, 100 143-144

Project Mercury, 93 of Gagarin, 143 see also Mercury flights Refueling
in space, 283

Project Orion, 287 Relativity, see General Theory

Propellants of Relativity future, 282 Relay, 123 liquid, 50-53,57,59
Rendezvous in space, 182, 238 and mass ratio, 78-84 Retrorockets, 170,
199 and the Moon, 236 Reynolds, Jim, 11, 13 of Saturn 5, 189, 194 Road
to Space Travel, The, solid, 47, 49, 50 38,122 today's chemical, 282
Robot vs.  man, 149 water as, 286Rocket engineers, German,

"Proton" satellites, 104 37-40,90,92,94

Proxima Centauri, 306, 310, "Rocket into Planetary Space, 312 The," 38
messages to, 324 Rocket propulsion and Cyrano, 22 travel to, 326, 327,
331-333 and Goddard, 32-37, 44

Purcell, Dr.  Edward, 325,330 and Oberth, 37-39

Pythagoras, 19principles of, 41-46, 79-85 and Tsiolkovsky, 31-32

Radiation Rockets as danger to astronauts, 146 bounced off planets,
259, 289 infrared, 121 Chinese and, 48 solar, 101, 109 electric, 287

Van Allen belt, 102, 105-106 exhaust speeds of, 77-81

Radio astronomy, 111, 230, and IGY, 91-95 320-322 Indians and, 48

Radio Corporation of America, and infrared radiation, 121 and Jules
Verne, 23-24 124 multistage, 27, 33

Radio emissions, from Jupiter, nuclear, 285 275 refueling in space,
181

Radio signal to stars, 319-320 solar-powered, 290

Ramjet solid-fueled, 47-49, 50 and Cyrano, 22and Tsiolkovsky, 31-32
interstellar, 327-328, 332 in vacuum, 41-46

Ranger spacecraft, 165, 166, Rockets, Missiles, and Space, 167,168,169
Travel, 39

Rosen, Dr.  Harold, 125

Reaction and rocket propul- Ross, H. E."  xvii, 12 sion, 42-46Russia,
see Soviet Union

Redstone missile, 91, 92, 94, 95 Sagan, Dr.  Carl, 295,335, and Oberth,
39-40 342,343

Index o 365

Sailboats, solar, 291 Saturn, 242, 246,261, 262

Samos reconnaissance atmosphere of, 274, 276 satellites, 101, 120,121
hazards of, 293

Siinger, Dr.  Eugen, 335 moons of, 276

San Marco project, 96 rings, 276

Satellites Saturn 5, 188

Alouette, 107, 110 and Crawler, 198 applications, 119 fuel pumps of,
189

Atlas-Score, 123 propellants for, 189, 194 automatic vs.  manned,
thrust of, 189 148-149,152Saturn vehicles, 107, 150 communications,
121-132 Scale model of Solar System,

Courier, 123 241-242,244

Echo'IZ3Science fiction, 23-29,

ESSA,"7 31-32

first artificial, 91-94 Science and Imagination, 29 geodetic, 104
Sedov, Leonid, 14 ground track of, 97 Seitz, Dr.  Frederick, 11
imaginary, 24-27 Sentry satellites, 121

Lunar Orbiter, 120, 14 1, Service Module (SM), 188, 177 193 202,210
lunar probe, 14 Service s,"ations in space, meteorological, 106, 119-
156'157 Midas, 121 Shepard, Alan, 136

Molmya, 129Shklovskii, I. S."  335,342, 343 navigational, 25, 113
Silicon-carbon compounds,

Nimbus, 117 279 nuclear-powered, 113 Sirius, 306

OAO, 109, 110 Sirius B, 313

OGO, 106 61 Cygni, 310

OSO,109

orbits of artificial, 73, 95Sled and bricks, 42, 44, 77, 79,
102,124-128 80 and orbital speed, 72 Smith, Ralph A."  12,183 polar
orbit, 96-98 Smithsonian Aerospace and precession, 100 Museum, 94
reconnaissance, 120, 121 Smithsonian Institution, 34

Relay, 124 Snark missile, 91 of Saturn, 277 Solar System 11
scientific," 103-110 "energy diagram of," 245

Sentry, 121 247 stability of, 94, 98-101

Syncom, lZ5-127 exploitation of, 281-282

Telstar 1, 123orbits of planets in, Z44 of Uranus, 277scale model of,
241-244

Vanguard, 94-95 statistics on,

Vela, 121 300-301 weather, 116,"9 Somnium, 21

Soviet Union Space probes, 253-259.  communications satellites,
Lunal,253 129 Mariners, 255-256

Cosmos satellites, 121, Mars 1, 255 121 n. sputnik 8, 254-255 and
German rocket scientists, 57, 90 Zond 3,169 and manned spacecraft,
135-136,140,143 Spaceship moon flights (Lunas), lunary-type, 15
163-164,169-170,173, multistage, 81-83 176,177-180,253-255 see also
Rockets

"Proton" satellites, 104 Space station, 38, 148-157 and reconnaissance
sat el- imaginary, 152 lites, 120 manned, 120,122 space capsules, 135,
136, uses of, 150, 156, 157, 283 140,143 and space flight, 90, 92
Spacesuits, 139, 145 space probes, 254-255 on Moon, 203

Sputniks, 95, 100, 135, 254 Space telescopes, 153 and Tsiolkovsky, 30
Space travel and U.S. reconnaissance, cost of, 237, 283 121 discomforts
of, 137 vehicle for sputnik, 90, 94 early books on, 11-14

Soyuz,136 and Goddard, 33-36

Space imaginary, 19-29 beginning of, 61-62, 63 and Jules Verne, 23-Z4
commercial uses of, 154-157 and launch speeds, 76-84 visitors from, 343
motives for, 348 space communications, 121and Oberth, 37-39 132 results
of, 350-354

Early Bird, 128-129 and TsiolkovskY, 30-32

Echo balloons, 123 Space Treaty, UN, 150

Intelsats, 129 Speed

Molmya, 129 cosmic," 76

Synooms, 125-127 orbital, 72, 82-83, 95

Telstar, 123-124 Speed of light see also Communications exceeding,
336

Satellite Corporation reaching, 327, 332-333

Spacecraft Sputnik 2, 95, 100, 135 atmosphere in, 140-142,145 Sputnik
8, 254 and heat, 141-144 Sputnik vehicle, 90, 94 and meteoroids, 107,
145 stalin, Joseph, 57, 90 re-entry of, 61, 143-144, 210

Space environments and Star clouds, 307, 311 planets, 293Star cluster,
globular, 312

Stars, 307-318Tennyson, Alfred, Lord, 19, beings among, 345 281
communication with, 319Theory of Relativity, see General Theory of
Relativity distances to, 306, 307 Thor-Abel-l booster, 163 novae,
313Thor Delta booster, 128 n. planets of, 310 Thor missile, 91 travel
to, 326 Thrust variety among, 305-306, of jet exhaust, 77 310-314 and
power source, 45

Steward Observatory, 153 of V-2, 53

Stewart, Dr.  Homer, 94 Thrust into Space, 286

Storms, solar, 109, 147 Tifft, Dr.  William, 153

Sun Tikhonravov, M. E."  31 escape velocity of, 74 Time, and Mechta
flight, 254 probe to, 253Time-dilation effect, 331, 332 rotation of,
312, 314 335 sailing by energy of, 291 Tiros, 116,"7 solar flares, 109,
147 Titan booster, 140

Supernovae, 313Titan missile, 57, 58,91

Surveyors, 167,171-173 Titan (of Saturn), 276 photos from, 224, 236
fuel from, 276, 283

Syncom communications sat el- Tokyo Olympics, 126 lites, 119, 125-127,
129 Transit satellites, 25, 113, 121

True History, 20

Tektites, 143Tsien, Dr.  Hsue-Shen, 37 n.

Telephony and satellites, 128 Tsiolkovsky, Konstantin, 30

Telescope 32,37-38,85 invention of, 20 and "cosmic speed," 76,77
orbital, 110, 153 and man in space, 31, 133, radio, 230,321-322 302

TelevisionTsiolkovsky crater, 33, 218 intercontinental, 123-124, Tycho
crater, 124 129 Tycho's nova, 313 and lunar mission, 209-210 and photos
of Moon, 16.5, 168 Unidentified Flying Objects

Television and Infrared Obser- (UFO's), 339-343 vat ion Satellite
Mros), U.S.SK."  see Soviet Union 116,"7 Universe

Telstar communications sat el- scale model of, 242,244 lite, 123-126,
127 size of, 21

Temperature see also Solar System on Jupiter, 297 on Mars,
267University of Chicago, 297 on Mercury, 271 Unwin, J. D."  349 on
Moon, 216, 222 Uranium and atomic rockets, on Pluto, 278, 293 286 in
space, 62-63 Uranus, 242, 246, 274 on Venus, 263, 297 satellites of,
277

Vacuum Voyage to the Moon, 28 exposure to, 146 Voyage to the Sun, 290
and rocket propulsion, 34, Voyager spacecraft, 269 41-46Voyages to the
Moon and Sun,

Van Allen, Dr.  James, 106 22

Van Allen radiation belt, 95, V-2 rockets, 37, 39, 53-59 102,157 mass
ratio of, 80

Vanguard vehicle, 94, 95, 165 and Russians, 57, 90

Vehicle Assembly Building and Saturn, 5, 188 (VAB), 187, 197-198, 199
and U.S. Army, 57,89

Vela satellites, 121

Velocity War, rockets and, 48 from Earth into space, 71Water 85,
249-254, 257, 258 for astrouauts, 141 for interplanetary travel, and
life, 278 300-301 on Moon, 233, 235 for interstellar travel, 331as
propellant, 286 332,333Weather satellites, 114-115,

Venus, 242, 246,295 119-120 fly-by, 254, 258, 263 n. Webb, NASA
Administrator gravity on, C-~) James, 14 journey to, 248-249, 25 1,
Webster, Senator Daniel, 11 255,257 Weightlessness orbit of, 75and
orbital hospital, 155 surface of, 262-263, 295 and space flight,
133-136

Venus probe, 76Wells, H. G."  21, 27-Z8, 288,

Verein fijr Raumschiffahrt, 38, 52 354

Wexler, Dr.  Harry, 116

Verne, Jules, 23-24, 27, 37, 211

Viking rocket, 89, 93 White Sands Proving Ground,

Voltaire, 22 89 von Braun, Dr.  Wernher, 14, Wilkins, Bishop, 22 37
World, the Flesh, and the and Apollo, 189 Devil, The, 328 and Redstone,
92, 94-95 Wright brothers, 47, 347 and V-2, 52, 57, 90 von Hoemer, Dr.
Se;bastian, X-ray astronomy, 228 330 n."  334 von Pirquet, Baron Guido,
183

Voshkod,136,140 Zond 2, 255

Vostok 1, 135, 136, 138, 139, Zond 3, 169 140Zwicky, Professor Fritz,
164 n.

