Dedicated, with respectful admiration, to two great Russians, both depicted herein: General Alexei Leonov - Cosmonaut, Hero of the Soviet Union, Artist and Academician Andrei Sakharov - Scientist, Nobel Laureate, Humanist.

Author's Note

The novel 2001: A Space Odyssey was written during the years 1964-8 and was published in July 1968, shortly after release of the movie. As I have described in The Lost Worlds of 2001, both projects proceeded simultaneously, with feedback in each direction. Thus I often had the strange experience of revising the manuscript after viewing rushes based upon an earlier version of the story - a stimulating, but rather expensive, way of writing a novel.

As a result, there is a much closer parallel between book and movie than is usually the case, but there are also major differences. In the novel, the destination of the spaceship Discovery was Iapetus (or Japetus), most enigmatic of Saturn's many moons. The Saturnian system was reached via Jupiter: Discovery made a close approach to the giant planet, using its enormous gravitational field to produce a 'slingshot' effect and to accelerate it along the second lap of its journey. Exactly the same manoeuvre was used by the Voyager space probes in 1979, when they made the first detailed reconnaissance of the outer giants.

In the movie, however, Stanley Kubrick wisely avoided confusion by setting the third confrontation between Man and Monolith among the moons of Jupiter. Saturn was dropped from the script entirely, though Douglas Trumbull later used the expertise he had acquired to film the ringed planet in his own production, Silent Running.

No one could have imagined, back in the mid-sixties, that the exploration of the moons of Jupiter lay, not in the next century, but only fifteen years ahead. Nor had anyone dreamed of the wonders that would be found there - although we can be quite certain that the discoveries of the twin Voyagers will one day be surpassed by even more unexpected finds. When 2001 was written, Io, Europa, Ganymede, and Callisto were mere pinpoints of light in even the most powerful telescope; now they are worlds, each unique, and one of them - Io - is the most volcanically active body in the Solar System.

Yet, all things considered, both movie and book stand up quite well in the light of these discoveries, and it is fascinating to compare the Jupiter sequences in the film with the actual movies from the Voyager cameras. But clearly, anything written today has to incorporate the results of the 1979 explorations: the moons of Jupiter are no longer uncharted territory.

And there is another, more subtle, psychological factor to be taken into consideration. 2001 was written in an age that now lies beyond one of the Great Divides in human history; we are sundered from it forever by the moment when Neil Armstrong set foot upon the Moon. The date 20 July 1969 was still half a decade in the future when Stanley Kubrick and I started thinking about the 'proverbial good science-fiction movie' (his phrase). Now history and fiction have become inextricably intertwined.

The Apollo astronauts had already seen the film when they left for the Moon. The crew of Apollo 8, who at Christmas 1968 became the first men ever to set eyes upon the Lunar Farside, told me that they had been tempted to radio back the discovery of a large black monolith: alas, discretion prevailed.

And there were, later, almost uncanny instances of nature imitating art. Strangest of all was the saga of Apollo 13 in 1970.

As a good opening, the Command Module, which houses the crew, had been christened Odyssey, Just before the explosion of the oxygen tank that caused the mission to be aborted, the crew had been playing Richard Strauss's Zarathustra theme, now universally identified with the movie. Immediately after the loss of power, Jack Swigert radioed back to Mission Control: 'Houston, we've had a problem.' The words that Hal used to astronaut Frank Poole on a similar occasion were: 'Sorry to interrupt the festivities, but we have a problem.'

When the report of the Apollo 13 mission was later published, NASA Administrator Tom Paine sent me a copy, and noted under Swigert's words: 'Just as you always said it would be, Arthur.' I still get a very strange feeling when I contemplate this whole series of events - almost, indeed, as if I share a certain responsibility.

Another resonance is less serious, but equally striking. One of the most technically brilliant sequences in the movie was that in which Frank Poole was shown running round and round the circular trick of the giant centrifuge, held in place by the 'artificial gravity' produced by its spin.

Almost a decade later, the crew of the superbly successful Skylab realized that its designers had provided them with a similar geometry; a ring of storage cabinets formed a smooth, circular hand around the space station's interior. Skylab, however, was not spinning, but this did not.deter its ingenious occupants. They discovered that they could run around the track, just like mice in a squirrel cage, to produce a result visually indistinguishable from that shown in 2001. And they televised the whole exercise back to Earth (need I name the accompanying music?) with the comment:

'Stanley Kubrick should see this.' As in due course he did, because I sent him the telecine recording. (I never got it back; Stanley uses a tame Black Hole as a filing system.)

Yet another link between film and reality is the painting by Apollo-Soyuz Commander, Cosmonaut Alexei Leonov, 'Near the Moon'. I first saw it in 1968, when 2001 was presented at the United Nations Conference on the Peaceful Uses of Outer Space. Immediately after the screening, Alexei pointed out to me that his concept (on page 32 of the Leonov-Sokolov book The Stars Are Awaiting Us, Moscow, 1967) shows exactly the same line-up as the movie's opening: the Earth rising beyond the Moon, and the Sun rising beyond them both. His autographed sketch of the painting now hangs on my office wall; for further details see Chapter 12.

Perhaps this is the appropriate point to identify another and less well-known name appearing in these pages, that of Hsue-shen Tsien. In 1936, with the great Theodore von Karman and Frank J. Malina, Dr Tsien founded the Guggenheim Aeronautical Laboratory of the California Institute of Technology (GALCIT) - the direct ancestor of Pasadena's famed Jet Propulsion Laboratory. He was also the first Goddard Professor at Caltech, and contributed greatly to American rocket research through the 1940s. Later, in one of the most disgraceful episodes of the McCarthy period, he was arrested on trumped-up security charges when he wished to return to his native country. For the last two decades, he has been one of the leaders of the Chinese rocket programme.

Finally, there is the strange case of the 'Eye of Japetus' - Chapter 35 of 2001. Here I describe astronaut Bowman's discovery on the Saturnian moon of a curious feather 'a brilliant white oval, about four hundred miles long and two hundred wide... perfectly symmetrical... and so sharp-edged that it almost looked... painted on the face of the little moon.' As he came closer, Bowman convinced himself that 'the bright ellipse set against the dark background of the satellite was a huge empty eye staring at him as he approached...' Later, he noticed 'the tiny black dot at the exact centre', which turns out to be the Monolith (or one of its avatars).

Well, when Voyager 1 transmitted the first photographs of Iapetus, they did indeed disclose a large, clear-cut white oval with a tiny black dot at the centre. Carl Sagan promptly sent me a print from the Jet Propulsion Laboratory with the cryptic annotation 'Thinking of you...' I do not know whether to be relieved or disappointed that Voyager 2 has left the matter still open.

Inevitably, therefore, the story you are about to read is something much more complex than a straightforward sequel to the earlier novel - or the movie. Where these differ, I have followed the screen version; however, I have been more concerned with making this book self-consistent, and as accurate as possible in the light of current knowledge.

Which, of course, will once more be out of date by 2001...

Arthur C. Clarke

COLOMBO, SRI LANKA

JANUARY 1982

I

LEONOV

1

Meeting at the Focus

Even in this metric age, it was still the thousand-foot telescope, not the three-hundred-metre one. The great saucer set among the mountains was already half full of shadow, as the tropical sun dropped swiftly to rest, but the triangular raft of the antenna complex suspended high above its centre still blazed with light. From the ground far below, it would have taken keen eyes to notice the two human figures in the aerial maze of girders, support cables, and wave-guides.

'The time has come,' said Dr Dimitri Moisevitch to his old friend Heywood Floyd, 'to talk of many things. Of shoes and spaceships and sealing wax, but mostly of monoliths and malfunctioning computers.'

'So that's why you got me away from the conference. Not that I really mind - I've heard Carl give that SETI speech so many times that I can recite it myself. And the view certainly is fantastic - you know, all the times I've been to Arecibo, I've never made it up here to the antenna feed.'

'Shame on you. I've been here three times. Imagine - we're listening to the whole universe - but no one can overhear us. So let's talk about your problem.'

'What problem?'

'To start with, why you had to resign as Chairman of the National Council on Astronautics.'

'I didn't resign. The University of Hawaii pays a lot better.'

'Okay - you didn't resign - you were one jump ahead of them. After all these years, Woody, you can't fool me, and you should give up trying. If they offered the NCA back to you right now, would you hesitate?'

'All right, you old Cossak. What do you want to know?'

'First of all, there are lots of loose ends in the report you finally issued after so much prodding. We'll overlook the ridiculous and frankly illegal secrecy with which your people dug up the Tycho monolith -'

'That wasn't my idea.'

'Glad to hear it: I even believe you. And we appreciate the fact that you're now letting everyone examine the thing - which of course is what you should have done in the first place. Not that it's done much good...'

There was a gloomy silence while the two men contemplated the black enigma up there on the Moon, still contemptuously defying all the weapons that human ingenuity could bring to bear upon it. Then the Russian scientist continued.

'Anyway, whatever the Tycho monolith may be, there's something more important out at Jupiter. That's where it sent its signal, after all. And that's where your people ran into trouble. Sorry about that, by the way - though Frank Poole was the only one I knew personally. Met him at the '98 IAF Congress - he seemed a good man.'

'Thank you; they were all good men. I wish we knew what happened to them.'

'Whatever it was, surely you'll admit that it now concerns the whole human race - not merely the United States. You can no longer try to use your knowledge for purely national advantage.'

'Dimitri - you know perfectly well that your side would have done exactly the same thing. And you'd have helped.'

'You're absolutely right. But that's ancient history - like the just-departed administration of yours that was responsible for the whole mess. With a new President, perhaps wiser counsels will prevail.'

'Possibly. Do you have any suggestions, and are they official or just personal hopes?'

'Entirely unofficial at the moment. What the bloody politicians call exploratory talks. Which I shall flatly deny ever occurred.'

'Fair enough. Go on.'

'Okay - here's the situation. You're assembling Discovery 2 in parking orbit as quickly as you can, but you can't hope to have it ready in less than three years, which means you'll miss the next launch window -,

'I neither confirm nor deny. Remember I'm merely a humble university chancellor, the other side of the world from the Astronautics Council.'

'And your last trip to Washington was just a holiday to see old friends, I suppose. To continue: our own Alexei Leonov -,

'I thought you were calling it Gherman Titov.'

'Wrong, Chancellor. The dear old CIA's let you down again. Leonov it is, as of last January. And don't let anyone know I told you it will reach Jupiter at least a year ahead of Discovery.'

'Don't let anyone know I told you we were afraid of that. But do go on.'

'Because my bosses are just as stupid and shortsighted as yours, they want to go it alone. Which means that whatever went wrong with you may happen to us, and we'll all be back to square one - or worse.'

'What do you think went wrong? We're just as baffled as you are. And don't tell me you haven't got all of Dave Bowman's transmissions.'

'Of course we have. Right up to that last "My God, it's full of stars!" We've even done a stress analysis on his voice patterns. We don't think he was hallucinating; he was trying to describe what he actually saw.'

'And what do you make of his doppler shift?'

'Completely impossible, of course. When we lost his signal, he was receding at a tenth of the speed of light. And he'd reached that in less than two minutes. A quarter of a million gravities!'

'So he must have been killed instantly.'

'Don't pretend to be naive, Woody. Your space-pod radios aren't built to withstand even a hundredth of that acceleration. If they could survive, so could Bowman - at least, until we lost contact.'

'Just doing an independent check on your deductions. From there on, we're as much in the dark as you are. If you are.'

'Merely playing with lots of crazy guesses I'd be ashamed to tell you. Yet none of them, I suspect, will be half as crazy as the truth.'

In small crimson explosions the navigation warning lights winked on all around them, and the three slim towers supporting the antenna complex began to blaze like beacons against the darkling sky. The last red sliver of the sun vanished below the surrounding hills; Heywood Floyd waited for the Green Flash, which he had never seen. Once again, he was disappointed.

'So, Dimitri,' he said, 'let's get to the point. Just what are you driving at?'

'There must be a vast amount of priceless information stored in Discovery's data banks; presumably it's still being gathered, even though the ship's stopped transmitting. We'd like to have that.'

'Fair enough. But when you get out there, and Leonov makes a rendezvous, what's to prevent you from boarding Discovery and copying everything you want?'

'I never thought I'd have to remind you that Discovery is United States territory, and an unauthorized entry would be piracy.'

'Except in the event of a life-or-death emergency, which wouldn't be difficult to arrange. After all, it would be hard for us to check what your boys were up to, from a billion kilometres away.'

'Thanks for the most interesting suggestion; I'll pass it on. But even if we went aboard, it would take us weeks to learn all your systems, and read out all your memory banks. What I propose is cooperation. I'm convinced that's the best idea - but we may both have a job selling it to our respective bosses.'

'You want one of our astronauts to fly with Leonov?'

'Yes - preferably an engineer who's specialized in Discovery's systems. Like the ones you're training at Houston to bring the ship home.'

'How did you know that?'

'For heaven's sake, Woody - it was on Aviation Week's videotext at least a month ago.'

'I am out of touch; nobody tells me what's been declassified.'

'All the more reason to spend time in Washington. Will you back me up?'

'Absolutely. I agree with you one hundred per cent. But -'

'But what?'

'We both have to deal with dinosaurs with brains in their tails. Some of mine will argue: Let the Russians risk their necks, hurrying out to Jupiter. We'll be there anyway a couple of years later - and what's the hurry?'

For a moment there was silence on the antenna raft, except for a faint creak from the immense supporting cables that held it suspended a hundred metres in the sky. Then Moisevitch continued, so quietly that Floyd had to strain to hear him: 'Has anyone checked Discovery's orbit lately?'

'I really don't know - but I suppose so. Anyway, why bother? It's a perfectly stable one.'

'Indeed. Let me tactlessly remind you of an embarrassing incident from the old NASA days. Your first space station - Skylab. It was supposed to stay up at least a decade, but you didn't do your calculations right. The air drag in the ionosphere was badly underestimated, and it came down years ahead of schedule. I'm sure you remember that little cliffhanger, even though you were a boy at the time.'

'It was the year I graduated, and you know it. But Discovery doesn't go anywhere near Jupiter. Even at perigee - er, perijove - it's much too high to be affected by atmospheric drag.'

'I've already said enough to get me exiled to my dacha again - and you might not be allowed to visit me next time. So just ask your tracking people to do their job more carefully, will you? And remind them that Jupiter has the biggest magnetosphere in the Solar System.'

'I understand what you're driving at - many thanks. Anything else before we go down? I'm starting to freeze.'

'Don't worry, old friend. As soon as you let all this filter through to Washington - wait a week or so until I'm clear -things are going to get very, very hot.'

2

The House of the Dolphins

The dolphins swam into the dining room every evening, just before sunset. Only once since Floyd had occupied the Chancellor's residence had they broken their routine. That was the day of the '05 tsunami, which, fortunately, had lost most of its power before it reached Hilo. The next time his friends failed to turn up on schedule, Floyd would throw the family into the car and head for high ground, in the general direction of Mauna Kea.

Charming though they were, he had to admit that their playfulness was sometimes a nuisance. The wealthy marine geologist who had designed the house had never minded getting wet because he usually wore bathing trunks - or less. But there had been one unforgettable occasion when the entire Board of Regents, in full evening attire, had been sipping cocktails around the pool while awaiting the arrival of a distinguished guest from the mainland. The dolphins had deduced, correctly, that they would get second billing. So the visitor was quite surprised to be greeted by a bedraggled committee in ill-fitting bathrobes - and the buffet had been very salty.

Floyd often wondered what Marion would have thought of his strange and beautiful home on the edge of the Pacific. She had never liked the sea, but the sea had won in the end. Though the image was slowly fading, he could still recall the flashing screen on which he had first read the words: DR FLOYD - URGENT AND PERSONAL. And then the scrolling lines of fluorescent print that had swiftly burned their message into his mind:

REGRET TO INFORM YOU LONDON-WASHINGTON FLIGHT 452 REPORTED DOWN OFF NEWFOUNDLAND. RESCUE CRAFT PROCEEDING TO LOCATION BUT FEAR NO SURVIVORS.

Apart from an accident of fate, he would have been on that flight. For a few days, he had almost regretted the European Space Administration business that had delayed him in Paris; that haggle over the Solaris payload had saved his life.

And now, he had a new job, a new home and a new wife. Fate had also played an ironic role here. The recriminations and inquiries over the Jupiter mission had destroyed his Washington career, but a man of his ability was never unemployed for long. The more leisurely tempo of university life had always appealed to him, and when combined with one of the world's most beautiful locations it had proved irresistible. He had met the woman who was to be his second wife only a month after he had been appointed, while watching the fire fountains of Kilauea with a crowd of tourists.

With Caroline he had found the contentment that is just as important as happiness, and longer lasting. She had been a good stepmother to Marion's two daughters, and had given him Christopher. Despite the twenty-year age difference between them, she understood his moods and could wean him out of his occasional depressions. Thanks to her, he could now contemplate the memory of Marion without grief, though not without a wistful sadness that would remain with him for the rest of his life.

Caroline was throwing fish to the largest dolphin - the big male they called Scarback - when a gentle tickling on Floyd's wrist announced an incoming call. He tapped the slim metal band to quench the silent alarm and forestall the audible one, then walked to the nearest of the comsets scattered around the room.

'Chancellor here. Who's calling?'

'Heywood? This is Victor. How are you?'

In a fraction of a second, a whole kaleidoscope of emotions flashed through Floyd's mind. First there was annoyance: his successor - and, he was sure, principal contriver of his downfall - had never once attempted to contact him since his departure from Washington. Then came curiosity: what did they have to talk about? Next was a stubborn determination to be as unhelpful as possible, then shame at his own childishness, and, finally, a surge of excitement. Victor Millson could be calling for only one reason.

In as neutral a voice as he could muster, Floyd answered:

'I can't complain, Victor. What's the problem?'

'Is this a secure circuit?'

'No, thank God. I don't need them any more.'

'Um. Well, I'll put it this way. You recall the last project you administered?'

'I'm not likely to forget, especially as the Subcommittee on Astronautics called me back to give more evidence only a month ago.'

'Of course, of course. I really must get around to reading your statement, when I have a moment. But I've been so busy with the follow-up, and that's the problem.'

'I thought that everything was right on schedule.'

'It is - unfortunately. There's nothing we can do to advance it; even the highest priority would make only a few weeks' difference. And that means we'll be too late.'

'I don't understand,' said Floyd innocently. 'Though we don't want to waste time, of course, there's no real deadline.'

'Now there is - and two of them.'

'You amaze me.'

If Victor noticed any irony, he ignored it. 'Yes, there are two deadlines - one man-made, one not. It now turns out that we won't be the first to get back to the - er, scene of the action. Our old rivals will beat us by at least a year.'

'Too bad.'

'That's not the worst. Even if there were no competition, we'd be too late. There wouldn't be anything there when we arrive.'

'That's ridiculous. I'm sure I'd have heard if Congress had repealed the law of gravitation.'

'I'm serious. The situation isn't stable - I can't give details now. Will you be in for the rest of the evening?'

'Yes,' Floyd answered, realizing with some pleasure that it must now be well after midnight in Washington.

'Good. You'll have a package delivered within the hour. Call me back as soon as you've had the time to study it.'

'Won't it be rather late by then?'

'Yes, it will be. But we've wasted too much time already. I don't want to lose any more.'

Millson was true to his word. Exactly an hour later a large sealed envelope was delivered by an Air Force colonel, no less, who sat patiently chatting with Caroline while Floyd read its contents. 'I'm afraid I'll have to take it away when you've finished,' the high-ranking messenger boy said apologetically.

'I'm glad to hear it,' Floyd answered, as he settled down in his favourite reading hammock.

There were two documents, the first very short. It was stamped TOP SECRET, though the TOP had been crossed out and the modification endorsed by three signatures, all completely illegible. Obviously an extract from some much longer report, it had been heavily censored and was full of blanks, which made it most annoying to read. Fortunately, its conclusions could be summed up in one sentence: The Russians would reach Discovery long before its rightful owners could do so. As Floyd already knew this, he turned quickly to the second document - though not before noticing with satisfaction that this time they'd managed to get the name right. As usual, Dimitri had been perfectly accurate. The next manned expedition to Jupiter would travel aboard spacecraft Cosmonaut Alexei Leonov.

The second document was much longer and was merely confidential; indeed, it was in the form of a draft letter to Science, awaiting final approval before publication. Its snappy title was 'Space Vehicle Discovery: Anomalous Orbital Behavior'.

Then followed a dozen pages of mathematics and astronomical tables. Floyd skimmed through these, picking out the words from the music, and trying to detect any note of apology or even embarrassment. When he had finished, he was compelled to give a smile of wry admiration. No one could possibly guess that the tracking stations and ephemeris calculators had been caught by surprise, and that a frantic cover-up was in progress. Heads would doubtless roll, and he knew that Victor Millson would enjoy rolling them - if his was not one of the first to go. Though to do him justice, Victor had complained when Congress had cut funds for the tracking network. Maybe that would get him off the hook.

'Thank you, Colonel,' said Floyd when he had finished skimming the papers. 'Quite like old times, having classified documents. That's one thing I don't miss.'

The colonel placed the envelope carefully back in his briefcase, and activated the locks.

'Dr Millson would like you to return his call as soon as possible.'

'I know. But I don't have a secure circuit, I've some important visitors coming shortly, and I'm damned if I'm driving down to your office in Hilo just to say I've read two documents. Tell him that I've studied them carefully and await any further communication with interest.'

For a moment it looked as if the colonel was going to argue. Then he thought better of it, made a stiff farewell, and departed morosely into the night.

'Now, what was all that about?' asked Caroline. 'We're not expecting any visitors tonight, important or otherwise.'

'I hate being pushed around, particularly by Victor Millson.'

'Bet he calls you back as soon as the colonel reports.'

'Then we must switch off video and make some party noises. But to be perfectly truthful, at this stage I really don't have anything to say.'

'About what, if I'm allowed to ask.'

'Sorry, dear. It seems that Discovery is playing tricks on us. We thought the ship was in a stable orbit, but it may be about to crash.'

'Into Jupiter?'

'Oh no - that's quite impossible. Bowman left it parked at the inner Lagrange point, on the line between Jupiter and Io. It should have stayed there, more or less, though the perturbations of the outer moons would have made it wander back and forth.

'But what's happening now is something very odd, and we don't know the full explanation. Discovery's drifting more and more rapidly toward Io - though sometimes it accelerates, and sometimes even moves backward. If it keeps this up, it will impact within two or three years.'

'I thought this couldn't happen in astronomy. Isn't celestial mechanics supposed to be an exact science? So we poor backward biologists were always being told.'

'It is an exact science, when everything is taken into account. But some very strange things go on around Io. Apart from its volcanoes, there are tremendous electrical discharges - and Jupiter's magnetic field is spinning round every ten hours. So gravitation isn't the only force acting on Discovery; we should have thought of this sooner - much sooner.'

'Well, it's not your problem anymore. You should be thankful for that.'

'Your problem' - the very expression that Dimitri had used. And Dimitri - cunning old fox! - had known him much longer than Caroline.

It might not be his problem, but it was still his responsibility. Though many others had been involved, in the final analysis he had approved the plans for the Jupiter Mission, and supervised their execution.

Even at the time, he had had qualms; his views as a scientist had conflicted with his duties as a bureaucrat. He could have spoken out, and opposed the old administration's shortsighted policies - though to what extent those had actually contributed to the disaster was still uncertain.

Perhaps it was best if he closed this chapter of his life, and focused all his thoughts and energies upon his new career. But in his heart he knew that was impossible; even if Dimitri had not revived old guilts, they would have surfaced of their own accord.

Four men had died, and one had disappeared, out there among the moons of Jupiter. There was blood on his hands, and he did not know how to wash them clean.

3

SAL 9000

Dr Sivasubramanian Chandrasegarampillai, Professor of Computer Science at the University of Illinois, Urbana, also had an abiding sense of guilt, but one very different from Heywood Floyd's. Those of his students and colleagues who often wondered if the little scientist was quite human would not have been surprised to learn that he never thought of the dead astronauts. Dr Chandra grieved only for his lost child, HAL 9000.

Even after all these years, and his endless reviews of the data radioed back from Discovery, he was not sure what had gone wrong. He could only formulate theories; the facts he needed were frozen in Hal's circuits, out there between Jupiter and Io.

The sequence of events had been clearly established, up to the moment of the tragedy; thereafter, Commander Bowman had filled in a few more details on the brief occasions when he had re-established contact. But knowing what happened did not explain why.

The first hint of trouble had been late in the mission, when Hal had reported the imminent failure of the unit that kept Discovery's main antenna aligned to Earth. If the half-billion-kilometre-long radio beam wandered off target, the ship would be blind, deaf, and dumb.

Bowman himself had gone out to retrieve the suspect unit, but when it was tested it appeared, to everyone's surprise, to be in perfectly good order. The automatic checking circuits could find nothing wrong with it. Nor could Hal's twin, SAL 9000, back on Earth, when the information was transmitted to Urbana.

But Hal had insisted on the accuracy of his diagnosis, making pointed remarks about 'human error'. He had suggested that the control unit be put back in the antenna until it finally failed, so that the fault could be precisely located. No one could think of any objection, for the unit could be replaced in minutes, even if it did break down.

Bowman and Poole, however, had not been happy; they both felt that something was wrong, though neither could pinpoint it. For months they had accepted Hal as the third member of their tiny world, and knew his every mood. Then the atmosphere aboard the ship had subtly altered; there was a sense of strain in the air.

Feeling rather like traitors - as a distraught Bowman had later reported to Mission Control - the human two-thirds of the crew had discussed what should be done if their colleague was indeed malfunctioning. In the worst possible case, Hal would have to be relieved of all his higher responsibilities. This would involve disconnection - the computer equivalent of death.

Despite their doubts, they had carried out the agreed programme. Poole had flown out of Discovery in one of the little space pods that served as transporters and mobile workshops during extravehicular activities. Since the somewhat tricky job of replacing the antenna unit could not be performed by the pod's own manipulators, Poole had started to do it himself.

What happened then had been missed by the external cameras, which was a suspicious detail in itself. Bowman's first warning of disaster was a cry from Poole - then, silence. A moment later he saw Poole, tumbling over and over, spinning away into space. His own pod had rammed him, and was itself blasting away out of control.

As Bowman admitted later, he had then made several serious mistakes - all but one excusable. In the hope of rescuing Poole, if he was still alive, Bowman launched himself in another space pod - leaving Hal in full control of the ship.

The EVA was in vain; Poole was dead when Bowman reached him. Numb with despair, he had carried the body back to the ship - only to be refused entry by Hal.

But Hal had underestimated human ingenuity and determination. Though he had left his suit helmet in the ship, and thus had to risk direct exposure to space, Bowman forced his way in by an emergency hatch not under computer control. Then he proceeded to lobotomize Hal, unplugging his brain modules one by one.

When he regained control of the ship, Bowman made an appalling discovery. During his absence, Hal had switched off the life-support systems of the three hibernating astronauts. Bowman was alone, as no man had ever been before in the whole of human history.

Others might have abandoned themselves in helpless despair, but now David Bowman proved that those who had selected him had indeed chosen well. He managed to keep Discovery operational, and even re-established intermittent contact with Mission Control, by orienting the whole ship so that the jammed antenna pointed toward Earth.

On its preordained trajectory, Discovery had finally arrived at Jupiter. There Bowman had encountered, orbiting among the moons of the giant planet, a black slab of exactly the same shape as the monolith excavated in the lunar crater Tycho - but hundreds of times larger. He had gone out in a space pod to investigate, and had disappeared leaving that final, baffling message: 'My God, it's full of stars!'

That mystery was for others to worry about; Dr Chandra's overwhelming concern was with Hal. If there was one thing his unemotional mind hated, it was uncertainty. He would never be satisfied until he knew the cause of Hal's behaviour. Even now, he refused to call it a malfunction; at most, it was an 'anomaly'.

The tiny cubbyhole he used as his inner sanctum was equipped only with a swivel chair, a desk console, and a blackboard flanked by two photographs. Few members of the general public could have identified the portraits, but anyone permitted thus far would have recognized them instantly as John von Neumann and Alan Turing, the twin gods of the computing pantheon.

There were no books, and not even paper and pencil on the desk. All the volumes in all the libraries of the world were instantly available at the touch of Chandra's fingers, and the visual display was his sketchbook and writing pad. Even the blackboard was used only for visitors; the last half - erased block diagram upon it bore a date already three weeks in the past.

Dr Chandra lit one of the venomous cheroots which he imported from Madras, and which were widely - and correctly - believed to be his only vice. The console was never switched off he checked that no messages were flashing importantly on the display, then spoke into the microphone.

'Good morning, Sal. So you've nothing new for me?'

'No, Dr Chandra. Have you anything for me?'

The voice might have been that of any cultured Hindu lady educated in the United States as well as her own country. Sal's accent had not started that way, but over the years she had picked up many of Chandra's intonations.

The scientist tapped out a code on the board, switching Sal's inputs to the memory with the highest security rating. No one knew that he talked to the computer on this circuit as he never could to a human being. No matter that Sal did not really understand more than a fraction of what he said; her responses were so convincing that even her creator was sometimes deceived. As indeed he wished to be: these secret communications helped to preserve his mental equilibrium - perhaps even his sanity.

'You've often told me, Sal, that we cannot solve the problem of Hal's anomalous behaviour without more information. But how can we get that information?'

'That is obvious. Someone must return to Discovery.'

'Exactly. Now it looks as if that is going to happen, sooner than we expected.'

'I am pleased to hear that.'

'I knew that you would be,' answered Chandra, and meant it. He had long since broken off communications with the dwindling body of philosophers who argued that computers could not really feel emotions, but only pretended to do so.

('If you can prove to me that you're not pretending to be annoyed,' he had once retorted scornfully to one such critic, 'I'll take you seriously.' At that point, his opponent had put on a most convincing imitation of anger.)

'Now I want to explore another possibility,' Chandra continued. 'Diagnosis is only the first step. The process is incomplete unless it leads to a cure.'

'You believe that Hal can be restored to normal functioning?'

'I hope so. I do not know. There may have been irreversible damage, and certainly major loss of memory.'

He paused thoughtfully, took several puffs, then blew a skilful smoke ring that scored a bull's-eye on Sal's wideangle lens. A human being would not have regarded this as a friendly gesture; that was yet another of the many advantages of computers.

'I need your cooperation, Sal.'

'Of course, Dr Chandra.'

'There may be certain risks.'

'What do you mean?'

'I propose to disconnect some of your circuits, particularly those involving your higher functions. Does this disturb you?'

'I am unable to answer that without more specific information.'

'Very well. Let me put it this way. You have operated continuously, have you not, since you were first switched on?'

'That is correct.'

'But you are aware that we human beings cannot do so. We require sleep - an almost complete break in our mental functioning, at least on the conscious level.'

'I know this. But I do not understand it.'

'Well, you may be about to experience something like sleep. Probably all that will happen is that time will pass, but you will be unaware out. When you check your internal clock, you will discover that there are gaps in your monitor record. That is all.'

'But you said that there might be risks. What are they?'

'There is a very slight chance - it is impossible to compute it - that when I reconnect your circuits, there may be some changes in your personality, your future behaviour patterns. You may feel different. Not necessarily better, or worse.'

'I do not know what that means.'

'I'm sorry - it may not mean anything. So don't worry about it. Now please open a new file - here is the name.' Using the keyboard input, Chandra typed out: PHOENIX.

'Do you know what that is?' he asked Sal.

With no discernible pause the computer replied: 'There are twenty-five references in the current encyclopedia.'

'Which one do you think is relevant?'

'The tutor of Achilles?'

'Interesting. I didn't know that one. Try again.'

'A fabulous bird, reborn from the ashes of its earlier life.'

'Excellent. Now do you understand why I chose it?'

'Because you hope that Hal can be reactivated.'

'Yes - with your assistance. Are you ready?'

'Not yet. I would like to ask a question.'

'What is it?'

'Will I dream?'

'Of course you will. All intelligent creatures dream - but no one knows why.' Chandra paused for a moment, blew another smoke ring from the cheroot, and added something that he would never admit to a human being. 'Perhaps you will dream about Hal - as I often do.'

4

Mission Profile

English Version

To: Captain Tatiana (Tanya) Orlova, Commander. Spacecraft Cosmonaut Alexei Leonov (UNCOS Registration 081342).

From: National Council on Astronautics, Pennsylvania Avenue, Washington

Commission on Outer Space, USSR Academy of Science, Korolyev Prospect, Moscow

Mission Objectives

The objectives of your mission are, in order of priority:

1. To proceed to the Jovian system and rendezvous with US Spacecraft Discovery (UNCOS 01/283).

2. To board this spacecraft, and obtain all possible information relating to its earlier mission.

3. To reactivate Spacecraft Discovery's onboard systems and, if propellant supplies are adequate, inject the ship into an Earth-returns trajectory.

4 To locate the alien artifact encountered by Discovery, and to investigate it to the maximum extent possible by remote sensors.

5. If it seems advisable, and Mission Control concurs, to rendezvous with this object for closer inspection.

6. To carry out a survey of Jupiter and its satellites, as far as this is compatible with the above objectives.

It is realized that unforeseen circumstances may require a change of priorities, or even make it impossible to achieve some of these objectives. It must be clearly understood that the rendezvous with Spacecraft Discovery is for the express purpose of obtaining information about the artifact; this must take precedence over all other objectives, including attempts at salvage.

Crew

The crew of Spacecraft Alexei Leonov will consist of:

Captain Tatiana Orlova (Engineering-Propulsion)

Dr Vasili Orlov (Navigation-Astronomy)

Dr Maxim Brailovsky (Engineering-Structures)

Dr Alexander Kovalev (Engineering-Communications)

Dr Nikolai Ternovsky (Engineering-Control Systems)

Surgeon-Commander Katerina Rudenko (Medical-Life-Support)

Dr Irma Yakunina (Medical-Nutrition)

In addition, the US National Council on Astronautics will provide the following three experts:

Dr Heywood Floyd dropped the memorandum, and leaned back in his chair. It was all settled; the point of no return had been passed. Even if he wished to do so, there was no way to put back the clock.

He glanced across at Caroline, sitting with two-year-old Chris on the edge of the pool. The boy was more at home in the water than on land, and could stay submerged for periods that often terrified visitors. And though he could not yet speak much Human, he already seemed fluent in Dolphin.

One of Christopher's friends had just swum in from the Pacific and was presenting his back to be patted. You too are a wanderer, thought Floyd, in a vast and trackless ocean; but how small your tiny Pacific seems, against the immensity I am facing now!

Caroline became aware of his gaze, and rose to her feet. She looked at him sombrely, but without anger; all that had been burned out in the last few days. As she approached, she even managed a wistful smile.

'I've found that poem I was looking for,' she said. 'It starts like this:

What is a woman that you forsake her,

And the hearth-fire and the home acre,

To go with the old grey Widow-maker?'

'Sorry - I don't quite understand. Who is the Widow-maker?'

'Not who, what. The sea. The poem's a lament by a Viking woman. It was written by Rudyard Kipling, a hundred years ago.'

Floyd took his wife's hand; she did not respond, but neither did she resist.

'Well, I don't feel at all like a Viking. I'm not after loot, and adventure is the very last thing I want.'

'Then why - no, I don't intend to start another fight. But it would help us both, if you know exactly what your motives are.'

'I wish I could give you one single good reason. Instead, I've a whole host of little ones. But they add up to a final answer I can't argue with - believe me.'

'I believe you. But are you sure you're not fooling yourself?'

'If I am, then so are a lot of other people. Including, may I remind you, the President of the United States.'

'I'm not likely to forget. But suppose - just suppose - that he hadn't asked you. Would you have volunteered?'

'I can answer that truthfully: No. It would never have occurred to me. President Mordecai's call was the biggest shock of my life. But when I thought it over, I realized he was perfectly right. You know I don't go in for false modesty. I am the best-qualified man for the job - when the space docs give their final okay. And you should know that I'm still in pretty good shape.'

That brought the smile he had intended.

'Sometimes I wonder if you'd suggested it yourself.'

The thought had indeed occurred to him; but he could answer honestly.

'I would never have done so without consulting you.'

'I'm glad you didn't. I don't know what I'd have said.'

'I could still turn it down.'

'Now you're talking nonsense, and you know it. Even if you did, you'd hate me for the rest of your life - and you'd never forgive yourself. You have too strong a sense of duty. Maybe that's one of the reasons I married you.'

Duty! Yes, that was the key word, and what multitudes it contained. He had a duty to himself, to his family, to the University, to his past job (even though he had left it under a cloud), to his country - and to the human race. It was not easy to establish the priorities; and sometimes they conflicted with one another.

There were perfectly logical reasons why he should go on the mission - and equally logical reasons, as many of his colleagues had already pointed out, why he should not. But perhaps in the final analysis, the choice had been made by his heart, not his brain. And even here, emotion urged him in two opposite directions.

Curiosity, guilt, the determination to finish a job that had been badly botched - they all combined to drive him toward Jupiter and whatever might be waiting there. On the other hand, fear - he was honest enough to admit that - united with love of his family to keep him on Earth. Yet he had never had any real doubts; he had made his decision almost instantly, and had deflected all of Caroline's arguments as gently as he could.

And there was one other consoling thought that he had not yet risked sharing with his wife. Though he would be gone two and a half years, all but the fifty days at Jupiter would be spent in timeless hibernation. When he returned, the gap between their ages would have narrowed by more than two years.

He would have sacrificed the present so that they could share a longer future together.

5

Leonov

The months contracted to weeks, the weeks dwindled to days, the days shrivelled to hours; and suddenly Heywood Floyd was once more at the Cape - spaceward-bound for the first time since that trip to Clavius Base and the Tycho monolith, so many years ago.

But this time he was not alone, and there was no secrecy about the mission. A few seats ahead of him rode Dr Chandra, already engaged in a dialogue with his briefcase computer, and quite oblivious to his surroundings.

One of Floyd's secret amusements, which he had never confided to anyone, was spotting similarities between human beings and animals. The resemblances were more often flattering than insulting, and his little hobby was also a very useful aid to memory.

Dr Chandra was easy - the adjective birdlike sprang instantly to mind. He was tiny, delicate, and all his movements were swift and precise. But which bird? Obviously a very intelligent one. Magpie? Too perky and acquisitive. Owl? No - too slow-moving. Perhaps sparrow would do nicely.

Walter Curnow, the systems specialist who would have the formidable job of getting Discovery operational again, was a more difficult matter. He was a large, husky man, certainly not at all birdlike. One could usually find a match somewhere in the vast spectrum of dogs, but no canine seemed to fit. Of course - Curnow was a bear. Not the sulky, dangerous kind, but the friendly good-natured type. And perhaps this was appropriate; it reminded Floyd of the Russian colleagues he would soon be joining. They had been up in orbit for days, engaged in their final checks.

This is the great moment of my life, Floyd told himself. Now I am leaving on a mission that may determine the future of the human race. But he did not feel any sense of exultation; all he could think of, during the last minutes of the countdown, were the words he had whispered just before he had left home: 'Goodbye, my dear little son; will you remember me when I return?' And he still felt resentment toward Caroline because she would not awaken the sleeping child for one final embrace; yet he knew that she had been wise, and it was better that way.

His mood was shattered by a sudden explosive laugh; Dr Curnow was sharing a joke with his companions - as well as a large bottle that he handled as delicately as a barely subcritical mass of plutonium.

'Hey, Heywood,' he called, 'they tell me Captain Orlova's locked up all the drinks, so this is your last chance. Château Thierry '95. Sorry about the plastic cups.'

As Floyd sipped at the really superb champagne, he found himself cringing mentally at the thought of Curnow's guffaw reverberating all the way across the Solar System. Much as he admired the engineer's, ability, as a travelling companion Curnow might prove something of a strain. At least Dr Chandra would not present such problems; Floyd could hardly imagine him smiling, let alone laughing. And, of course, he turned down the champagne with a barely perceptible shudder. Curnow was polite enough, or glad enough, not to insist.

The engineer was, it seemed, determined to be the life and soul of the party. A few minutes later he produced a two-octave electronic keyboard, and gave rapid renderings of 'D'ye ken John Peel' as performed successively by piano, trombone, violin, flute, and full organ, with vocal accompaniment. He was really very good, and Floyd soon found himself singing along with the others. But it was just as well, he thought, that Curnow would spend most of the voyage in silent hibernation.

The music died with a sudden despairing discord as the engines ignited and the shuttle launched itself into the sky. Floyd was gripped by a familiar but always new exhilaration - the sense of boundless power, carrying him up and away from the cares and duties of Earth. Men knew better than they realized, when they placed the abode of the gods beyond the reach of gravity. He was flying toward that realm of weightlessness; for the moment, he would ignore the fact that out there lay not freedom, but the greatest responsibility of his career.

As the thrust increased, he felt the weight of worlds upon his shoulders - but he welcomed it, like an Atlas who had not yet tired of his burden. He did not attempt to think, but was content to savour the experience. Even if he was leaving Earth for the last time, and saying farewell to all that he had ever loved, he felt no sadness. The roar that surrounded him was a paean of triumph, sweeping away all minor emotions.

He was almost sorry when it ceased, though he welcomed the easier breathing and the sudden sense of freedom. Most of the other passengers started to unbuckle their safety straps, preparing to enjoy the thirty minutes of zero gravity during the transfer orbit, but a few who were obviously making the trip for the first time remained in their seats, looking around anxiously for the cabin attendants.

'Captain speaking. We're now at an altitude of three hundred kilometres, coming up over the west coast of Africa. You won't see much as it's night down there - that glow ahead is Sierra Leone - and there's a big tropical storm over the Gulf of Guinea. Look at those flashes!

'We'll have sunrise in fifteen minutes. Meanwhile I'm rolling the ship so you can get a good view of the equatorial satellite belt. The brightest one - almost straight overhead - is Intelsat's Atlantic-1 Antenna Farm. Then Intercosmos 2 to the west - that fainter star is Jupiter. And if you look just below that, you'll see a flashing light, moving against the star background - that's the new Chinese space-station. We pass within a hundred kilometres, not close enough to see anything with the naked eye -,

What were they up to? Floyd thought idly. He had examined the close-ups of the squat cylindrical structure with its curious bulges, and saw no reason to believe the alarmist rumours that it was a laser-equipped fortress. But while the Beijing Academy of Science ignored the UN Space Committee's repeated requests for a tour of inspection, the Chinese only had themselves to blame for such hostile propaganda.

The "Cosmonaut Alexei Leonov" was not a thing of beauty; but few spacecraft ever were. One day, perhaps, the human race would develop a new aesthetic; generations of artists might arise whose ideals were not based upon the natural forms of Earth moulded by wind and water. Space itself was a realm of often overpowering beauty; unfortunately, Man's hardware did not yet live up to it.

Apart from the four huge propellant tanks, which would be dropped off as soon as the transfer orbit was achieved, Leonov was surprisingly small. From heat shield to drive units was less than fifty metres; it was hard to believe that so modest a vehicle, smaller than many commercial aircraft, could carry ten men and women halfway across the Solar System.

But zero gravity, which made walls and roof and floor interchangeable, rewrote all the rules of living. There was plenty of room aboard Leonov even when everyone was awake at the same time, as was certainly the case at the moment. Indeed, her normal complement was at least doubled by assorted newsmen, engineers making final adjustments, and anxious officials.

As soon as the shuttle had docked, Floyd tried to find the cabin he would share - a year hence, when he awoke - with Curnow and Chandra. When he did locate it, he discovered that it was packed so tightly with neatly labelled boxes of equipment and provisions that entry was almost impossible. He was wondering glumly how to get a foot in the door when one of the crew, launching himself skilfully from handhold to handhold, noticed Floyd's dilemma and braked to a halt.

'Dr Floyd - welcome aboard. I'm Max Brailovsky - assistant engineer.'

The young Russian spoke the slow, careful English of a student who had had more lessons with an electronic tutor than a human teacher. As they shook hands, Floyd matched the face and name to the set of crew biographies he had already studied: Maxim Andreievitch Brailovsky, age thirty-one, born Leningrad, specializing in structure; hobbies: fencing, skycycling, chess.

'Glad to meet you,' said Floyd. 'But how do I get inside?'

'Not to worry,' said Max cheerfully. 'All that will be gone when you wake up. It's - what do you say? - expendables. We'll eat your room empty by the time you need it. I promise.' He patted his stomach.

'Fine - but meanwhile where do I put my things?' Floyd pointed to the three small cases, total mass fifty kilograms, which contained - he hoped - everything he needed for the next couple of billion kilometres. It had been no easy task, shepherding their weightless, but not inertialess, bulk through the ship's corridors with only a few collisions.

Max took two of the bags, glided gently through the triangle formed by three intersecting girders, and dived into a small hatchway, apparently defying Newton's First Law in the process. Floyd acquired a few extra bruises while following him; after a considerable time - Leonov seemed much bigger inside than out- they arrived at a door labelled CAPTAIN, in both Cyrillic and Roman. Although he could read Russian much better than he could speak it, Floyd appreciated the gesture; he had already noticed that all ship's notices were bilingual.

At Max's knock, a green light flashed on, and Floyd drifted inside as gracefully as he could. Though he had spoken to Captain Orlova many times, they had never before met. So he had two surprises.

It was impossible to judge a person's real size over the viewphone; the camera somehow converted everyone to the same scale. Captain Orlova, standing - as well as one could stand in zero gravity - barely reached to Floyd's shoulders. The viewphone had also completely failed to convey the penetrating quality of those dazzling blue eyes, much the most striking feature of a face that, at the moment, could not be fairly judged for beauty.

'Hello, Tanya,' said Floyd. 'How nice to meet at last. But what a pity about your hair.'

They grasped both hands, like old friends.

'And nice to have you aboard, Heywood!' answered the captain. Her English, unlike Brailovsky's, was quite fluent, though heavily accented. 'Yes, I was sorry to lose it - but hair's a nuisance on long missions, and I like to keep the local barbers away as long as possible. And my apologies about your cabin; as Max will have explained, we suddenly found we needed another ten cubic metres of storage space. Vasili and I won't be spending much time here for the next few hours - please feel free to use our quarters.'

'Thank you. What about Curnow and Chandra?'

'I've made similar arrangements with the crew. It may seem as if we're treating you like cargo -'

'Not wanted on voyage.'

'Pardon?'

'That's a label they used to put on the baggage, in the old days of ocean travel.'

Tanya smiled. 'It does look rather that way. But you'll be wanted all right, at the end of the trip. We're already planning your revival party.'

'That sounds too religious. Make it - no, resurrection would be even worse! - waking-up party. But I can see how busy you are - let me dump my things and continue my grand tour.'

'Max will show you around - take Dr Floyd to Vasili, will you? He's down in the drive unit.'

As they drifted out of the captain's quarters, Floyd gave mental good marks to the crew-selection committee. Tanya Orlova was impressive enough on paper; in the flesh she was almost intimidating, despite her charm. I wonder what she's like, Floyd asked himself, when she loses her temper. Would it be fire or ice? On the whole, I'd prefer not to find out.

Floyd was rapidly acquiring his space legs; by the time they reached Vasili Orlov, he was manoeuvring almost as confidently as his guide. The chief scientist greeted Floyd as warmly as his wife had.

'Welcome aboard, Heywood. How do you feel?'

'Fine, apart from slowly starving to death.'

For a moment Orlov looked puzzled; then his face split into a broad smile,

'Oh, I'd forgotten. Well, it won't be for long. In ten months' time, you can eat as much as you like.'

Hibernators went on a low-residue diet a week in advance; for the last twenty-four hours, they took nothing but liquid. Floyd was beginning to wonder how much of his increasing light-headedness was due to starvation, how much to Curnow's champagne, and how much to zero gravity.

To concentrate his mind, he scanned the multicoloured mass of plumbing that surrounded them.

'So this is the famous Sakharov Drive. It's the first time I've seen a full-scale unit.'

'It's only the fourth one ever built.'

'I hope it works.'

'It had better. Otherwise, the Gorky City Council will be renaming Sakharov Square again.'

It was a sign of the times that a Russian could joke, however wryly, about his country's treatment of its greatest scientist. Floyd was again reminded of Sakharov's eloquent speech to the Academy, when he was belatedly made Hero of the Soviet Union. Prison and banishment, he had told his listeners, were splendid aids to creativity; not a few masterpieces had been born within the walls of cells, beyond the reach of the world's distractions. For that matter, the greatest single achievement of the human intellect, the Principia itself, was a product of Newton's self-imposed exile from plague-ridden London.

The comparison was not immodest; from those years in Gorky had come not only new insights into the structure of matter and the origin of the Universe, but the plasma-controlling concepts that had led to practical thermonuclear power. The drive itself, though the best-known and most publicized outcome of that work, was merely one byproduct of that astonishing intellectual outburst. The tragedy was that such advances had been triggered by injustice; one day, perhaps, humanity would find more civilized ways of managing its affairs.

By the time they had left the chamber, Floyd had learned more about the Sakharov Drive than he really wished to know, or expected to remember. He was well acquainted with its basic principles - the use of a pulsed thermonuclear reaction to heat and expel virtually any propellant material. The best results were obtained with pure hydrogen as a working fluid, but that was excessively bulky and difficult to store over long periods of time. Methane and ammonia were acceptable alternatives; even water could be used, though with considerably poorer efficiency.

Leonov would compromise; the enormous liquid hydrogen tanks that provided the initial impetus would be discarded when the ship had attained the necessary speed to carry it to Jupiter. At the destination, ammonia would be used for the braking and rendezvous manoeuvres, and the eventual return to Earth.

That was the theory, checked and rechecked in endless tests and computer simulations. But as the ill-fated Discovery had shown so well, all human plans were subject to ruthless revision by Nature, or Fate, or whatever one preferred to call the powers behind the Universe.

'So there you are, Dr Floyd,' said an authoritative female voice, interrupting Vasili's enthusiastic explanation of magnetohydrodynamic feedback, 'Why didn't you report to me?'

Floyd rotated slowly on his axis by gently torquing himself with one hand. He saw a massive, maternal figure wearing a curious uniform adorned with dozens of pockets and pouches; the effect was not unlike that of a Cossack trooper draped with cartridge belts.

'Nice to meet you again, Doctor. I'm still exploring - I hope you've received my medical report from Houston.'

'Those vets at Teague! I wouldn't trust them to recognize foot-and-mouth disease!'

Floyd knew perfectly well the mutual respect felt between Katerina Rudenko and the Olin Teague Medical Center, even if the doctor's broad grin had not discounted her words. She saw his look of frank curiosity, and proudly fingered the webbing around her ample waist.

'The conventional little black bag isn't very practical in zero gravity - things float out of it and aren't there when you need them. I designed this myself, it's a complete minisurgery. With this, I could remove an appendix - or deliver a baby.'

'I trust that particular problem won't arise here.'

'Ha! A good doctor has to be ready for everything.'

What a contrast, thought Floyd, between Captain Orlova and Dr - or should he call her by her correct rank of Surgeon-Commander? - Rudenko. The captain had the grace and intensity of a prima ballerina; the doctor might have been the prototype of Mother Russia - stocky build, flat peasant face, needing only a shawl to complete the picture. Don't let that fool you, Floyd told himself. This is the woman who saved at least a dozen lives during the Komarov docking accident - and, in her spare time, manages to edit the Annals of Space Medicine. Consider yourself very lucky to have her aboard.

'Now, Dr Floyd, you're going to have plenty of time later to explore our little ship. My colleagues are too polite to say this, but they've work to do and you're in the way. I'd like to get you - all three of you - nice and peaceful as quickly as we can. Then we'll have less to worry about.'

'I was afraid of that, but I quite see your point of view. I'm ready as soon as you are.'

'I'm always ready. Come along - please.'

The ship's hospital was just large enough to hold an operating table, two exercise bicycles, a few cabinets of equipment, and an X-ray machine. While Dr Rudenko was giving Floyd a quick but thorough examination, she asked unexpectedly: 'What's that little gold cylinder Dr Chandra carries on the chain around his neck - some kind of communications device? He wouldn't take it off - in fact, he was almost too shy to take anything off.'

Floyd could not help smiling; it was easy to imagine the modest Indian's reactions to this rather overwhelming lady.

'It's a lingam.'

'A what?'

'You're the doctor - you ought to recognize it. The symbol of male fertility.'

'Of course - stupid of me. Is he a practising Hindu? It's a little late to ask us to arrange a strict vegetarian diet.'

'Don't worry - we wouldn't have done that to you without fair warning. Though he won't touch alcohol, Chandra's not fanatical about anything except computers. He once told me that his grandfather was a priest in Benares, and gave him that lingam - it's been in the family for generations.'

Rather to Floyd's surprise, Dr Rudenko did not show the negative reaction he had expected; indeed, her expression became uncharacteristically wistful.

'I understand his feeling. My grandmother gave me a beautiful icon - sixteenth century. I wanted to bring it - but it weighs five kilos.'

The doctor became abruptly businesslike again, gave Floyd a painless injection with a gas-gun hypodermic, and told him to come back as soon as he was sleepy. That, she assured him, would be in less than two hours.

'Meanwhile, relax completely,' she ordered. 'There's an observation port on this level - Station D.6. Why don't you go there?'

It seemed a good idea, and Floyd drifted away with a docility that would have surprised his friends. Dr Rudenko glanced at her watch, dictated a brief entry into her autosec, and set its alarm thirty minutes ahead.

When he reached the D.6 viewport, Floyd found Chandra and Curnow already there. They looked at him with a total lack of recognition, then turned once more toward the awesome spectacle outside. It occurred to Floyd - and he congratulated himself on such a brilliant observation - that Chandra could not really be enjoying the view. His eyes were tightly closed,

A totally unfamiliar planet hung there, gleaming with glorious blues and dazzling whites. How strange, Floyd told himself. What has happened to the Earth? Why, of course - no wonder he didn't recognize it! It was upside down! What a disaster - he wept briefly for all those poor people, falling off into space..

He barely noticed when two crew members removed Chandra's unresisting form. When they came back for Curnow, Floyd's own eyes were shut, but he was still breathing. When they returned for him, even his breathing had ceased.

II

TSIEN

6

Awakening

And they told us we wouldn't dream, thought Heywood Floyd, more with surprise than annoyance. The glorious pink glow that surrounded him was very soothing; it reminded him of barbecues and the crackling logs of Christmas fire. But there was no warmth; indeed, he felt a distinct though not uncomfortable coldness.

Voices were murmuring, just too softly for him to understand the words. They became louder - but still he could not understand.

'Surely,' he said in sudden amazement, 'I can't be dreaming in Russian!'

'No, Heywood,' answered a woman's voice. 'You're not dreaming. It's time to get out of bed.'

The lovely glow faded; he opened his eyes, and had a blurred glimpse of a flashlight being withdrawn from his face. He was lying on a couch, held against it by elastic webbing; figures were standing around him, but they were too out of focus to identify.

Gentle fingers closed his eyelids and massaged his forehead.

'Don't exert yourself. Breathe deeply... again... that's right... now how do you feel?'

'I don't know... strange... light-headed... and hungry.'

'That's a good sign. Do you know where you are? You can open your eyes now.'

The figures came into focus - first Dr Rudenko, then Captain Orlova. But something had happened to Tanya since he had seen her, only an hour ago. When Floyd identified the cause, it was almost a physical shock.

'You've grown your hair back!'

'I hope you think it's an improvement. I can't say the same about your beard.'

Floyd lifted his hand to his face, finding that he had to make a conscious effort to plan every stage of the movement. His chin was covered with short stubble - a two or three days' growth. In hibernation, hair grew at only a hundredth of its normal rate.

'So I made it,' he said. 'We've arrived at Jupiter.'

Tanya looked at him sombrely, then glanced at the doctor, who gave a barely perceptible nod.

'No, Heywood,' she said. 'We're still a month away. Don't be alarmed - the ship's fine, and everything's running normally. But your friends in Washington have asked us to wake you up ahead of time. Something very unexpected has happened. We're in a race to reach Discovery - and I'm afraid we're going to lose.'

7

Tsien

When Heywood Floyd's voice came from the comset speaker, the two dolphins suddenly stopped circling around the pool and swam over to its edge. They placed their heads on the rim and stared intently at the source of the sound.

So they recognize Heywood, thought Caroline, with a twinge of bitterness: Yet Christopher, crawling around his playpen, did not even stop playing with the colour controls of his picture book as his father's voice came loud and clear across half a billion kilometres of space.

'... My dear, you won't be surprised to hear from me, a month ahead of schedule; you'll have known for weeks that we have company out here.

'I still find it hard to believe; in some ways, it doesn't even make sense. They can't possibly have enough fuel for a safe return to Earth; we don't even see how they can make the rendezvous.

'We never saw them, of course. Even at its closest, Tsien was more than fifty million kilometres away. They had plenty of time to answer our signals if they wanted to, but they ignored us completely. Now they'll be much too busy for friendly chat. In a few hours they'll hit Jupiter's atmosphere - and then we'll see how well their aerobraking system works. If it does its job, that will be good for our morale. But if it fails, well, let's not talk about that.

'The Russians are taking it remarkably well, all things considered. They're angry and disappointed, of course - but I've heard many expressions of frank admiration. It was certainly a brilliant trick, building that ship in full view and making everyone think it was a spacestation until they hitched on those boosters.

'Well, there's nothing we can do, except watch. And at our distance, we won't have a much better view than your best telescopes. I can't help wishing them luck, though of course I hope they leave Discovery alone. That's our property, and I bet the State Department's reminding them of it, every hour on the hour.

'It's an ill wind - if our Chinese friends hadn't jumped the gun on us, you wouldn't have heard from me for another month. But now that Dr Rudenko's woken me up, I'll be speaking to you every couple of days.

'After the initial shock, I'm settling down nicely- getting to know the ship and its crew, finding my space legs. And polishing up my lousy Russian, though I don't have much chance of using it - everyone insists on speaking English.

What shocking linguists we Americans are! I sometimes feel ashamed of our chauvinism - or our laziness.

'The standard of on-board English ranges from absolutely perfect - Chief Engineer Sasha Kovalev could earn a living as a BBC announcer - down to the if-you-talk-fast-enough-it-doesn't-matter-how-many-mistakes-you-make variety. The only one who isn't fluent is Zenia Marchenko, who replaced Irma Yakunina at the last moment. Incidentally, I'm glad to hear that Irma made a good recovery - what a disappointment that must have been! I wonder if she's started hang-gliding again.

'And speaking of accidents, it's obvious that Zenia must also have had a very bad one. Though the plastic surgeons have done a remarkable job, you can tell that she must have been severely burned at some time. She's the baby of the crew and the others treat her with - I was going to say pity, but that's too condescending. Let's say with special kindness.

'Maybe you're wondering how I get on with Captain Tanya. Well, I like her very much - but I'd hate to make her angry. There's no doubt exactly who runs this ship.

'And Surgeon-Commander Rudenko - you met her at the Honolulu Aerospace Convention two years ago, and I'm sure you won't have forgotten that last party. You'll understand why we all call her Catherine the Great - behind her broad back, of course.

'But that's enough gossip. If I run overtime, I hate to think of the surcharge. And by the way, these personal calls are supposed to be completely private. But there are a lot of links in the communications chain, so don't be surprised if you occasionally get messages by - well, another route.

'I'll be waiting to hear from you - tell the girls I'll be speaking to them later. My love to you all - I miss you and Chris very badly. And when I get back, I promise I'll never leave again.'

There was a brief hissing pause, then an obviously synthetic voice said: 'This terminates Transmission Four Hundred Thirty-two Stroke Seven from Spacecraft Leonov.' As Caroline Floyd switched off the speaker, the two dolphins slid beneath the surface of the pool and glided out into the Pacific, leaving scarcely a ripple in the water.

When he realized that his friends were gone, Christopher began to cry. His mother picked him up in her arms and tried to comfort him, but it was a long time before she succeeded.

8

Transit of Jupiter

The image of Jupiter, with its ribbons of white cloud, its mottled bands of salmon pink, and the Great Red Spot staring out like a baleful eye, hung steady on the flight-deck projection screen. It was three-quarters full, but no one was looking at the illuminated disk; all eyes were focused on the crescent of darkness at its edge. There, over the nightside of the planet, the Chinese ship was about to meet its moment of truth.

This is absurd, thought Floyd. We can't possibly see anything across forty million kilometres. And it doesn't matter; the radio will tell us all we want to know.

Tsien had closed down all voice, video, and data circuits two hours before, as the long-range antennas were withdrawn into the protective shadow of the heat shield. Only the omnidirectional beacon was still transmitting, accurately pinpointing the Chinese ship's position as it plunged toward that ocean of continent-sized clouds. The shrill beep... beep... beep... was the only sound in Leonov's control room. Each of those pulses had left Jupiter more than two minutes earlier; by this time, their source might already be a cloud of incandescent gas, dispersing in the Jovian stratosphere.

The signal was fading, becoming noisy. The beeps were getting distorted; several dropped out completely, then the sequence returned. A plasma sheath was building up around Tsien and soon would cut off all communications until the ship re-emerged. If it ever did.

'Posmotri!' cried Max. 'There it is!'

At first Floyd could see nothing. Then, just off the edge of the illuminated disk, he made out a tiny star - gleaming where no star could possibly be, against the darkened face of Jupiter.

It appeared quite motionless, though he knew it must be moving at a hundred kilometres a second. Slowly it grew in brilliance; and then it was no longer a dimensionless point, but was becoming elongated. A man-made comet was streaking across the Jovian night sky, leaving a trail of incandescence thousands of kilometres in length.

One last badly distorted and curiously drawn-out beep sounded from the tracking beacon, then only the meaningless hiss of Jupiter's own radiation, one of those many cosmic voices that had nothing to do with Man or his works.

Tsien was inaudible, but not yet invisible. For they could see that the tiny elongated spark had indeed moved appreciably away from the sunward face of the planet and would soon disappear into the nightside. By then, if all had gone according to plan, Jupiter would have captured the ship, destroying its unwanted velocity. When it emerged from behind the giant world, it would be another Jovian satellite.

The spark flickered out. Tsien had rounded the curve of the planet and was heading over the nightside. There would be nothing to see, or to hear, until it emerged from shadow - if all went well, in just under an hour. It would be a very long hour for the Chinese.

To Chief Scientist Vasili Orlov and communications engineer Sasha Kovalev, the hour went extremely quickly. There was much they could learn from observations of that little star; its times of appearance and disappearance and, above all, the Doppler shift of the radio beacon gave vital information about Tsien's new orbit. Leonov's computers were already digesting the figures, and spitting out projected times of re-emergence based on various assumptions about rates of deceleration in the Jovian atmosphere.

Vasili switched off the computer display, spun around in his chair, loosened his seat belt, and addressed the patiently waiting audience.

'Earliest reappearance is in forty-two minutes. Why don't you spectators go for a walk, so we can concentrate on getting all this into good shape? See you in thirty-five minutes. Shoo! Nu ukhodi!'

Reluctantly, the unwanted bodies left the bridge - but, to Vasili's disgust, everyone was back again in little more than thirty minutes. He was still chiding them for their lack of faith in his calculations when the familiar beep... beep... beep... of Tsien's tracking beacon burst from the loudspeakers.

Vasili looked astonished and mortified, but soon joined in the spontaneous round of applause; Floyd could not see who first started the clapping. Rivals though they might be, they were all astronauts together, as far from home as any men had ever travelled - 'Ambassadors for Mankind', in the noble words of the first UN Space Treaty. Even if they did not want the Chinese to succeed, neither did they wish them to meet disaster.

A large element of self-interest was also involved, Floyd could not help thinking. Now the odds in Leonov's own favour were significantly improved; Tsien had demonstrated that the aerobraking manoeuvre was indeed possible. The data on Jupiter was correct; its atmosphere did not contain unexpected and perhaps fatal surprises.

'Well!' said Tanya. 'I suppose we should send them a message of congratulations. But even if we did, they wouldn't acknowledge it.'

Some of his colleagues were still making fun of Vasili, who was staring at his computer output in frank disbelief.

'I don't understand it!' he exclaimed. 'They should still be behind Jupiter! Sasha - give me a velocity reading on their beacon!'

Another silent dialogue was held with the computer; then Vasili gave a long, low whistle.

'Something's wrong. They're in a capture orbit, all right - but it won't let them make a rendezvous with Discovery. The orbit they're on now will take them way beyond Io - I'll have more accurate data when we've tracked them for another five minutes.'

'Anyway, they must be in a safe orbit,' said Tanya. 'They can always make corrections later.'

'Perhaps. But that could cost them days, even if they have the fuel. Which I doubt.'

'So we may still beat them.'

'Don't be such an optimist. We're still three weeks from Jupiter. They can make a dozen orbits before we get there, and choose the most favourable one for a rendezvous.'

'Again - assuming that they have enough propellant.'

'Of course. And that's something we can only make educated guesses about.'

All this conversation took place in such rapid and excited Russian that Floyd was left far behind. When Tanya took pity on him and explained that Tsien had overshot and was heading for the outer satellites, his first reaction was: 'Then they may be in serious trouble. What will you do if they appeal for help?'

'You must be making a joke. Can you imagine them doing that? They're much too proud. Anyway, it would be impossible. We can't change our mission profile, as you know perfectly well. Even if we had the fuel...'

'You're right, of course; but it might be difficult to explain that to the ninety-nine per cent of the human race that doesn't understand orbital mechanics. We should start thinking about some of the political complications - it would look bad for all of us if we can't help. Vasili, will you give me their final orbit, as soon as you've worked it out? I'm going down to my cabin to do some homework.'

Floyd's cabin, or rather one-third of a cabin, was still partly full of stores, many of them stacked in the curtained bunks that would be occupied by Chandra and Curnow when they emerged from their long slumbers. He had managed to clear a small working space for his personal effects and had been promised the luxury of another whole two cubic metres - just as soon as someone could be spared to help with the furniture removing.

Floyd unlocked his little communications console, set the decryption keys, and called for the information on Tsien that had been transmitted to him from Washington. He wondered if his hosts had had any luck in unscrambling it; the cipher was based on the product of two hundred-digit prime numbers, and the National Security Agency had staked its reputation on the claim that the fastest computer in existence could not crack it before the Big Crunch at the end of the Universe. It was a claim that could never be proved - only disproved.

Once again he stared intently at the excellent photographs of the Chinese ship, taken when it had revealed its true colours and was just about to leave Earth orbit. There were later shots - not so clear, because by then it had been far away from the prying cameras - of the final stage as it hurtled toward Jupiter. Those were the ones that interested him most; even more useful were the cutaway drawings and estimates of performance.

Granted the most optimistic assumptions, it was difficult to see what the Chinese hoped to do. They must have burned up at least ninety per cent of their propellant in that mad dash across the Solar System. Unless it was literally a suicide mission - something that could not be ruled out - only a plan involving hibernation and later rescue made any sense. And Intelligence did not believe that Chinese hibernation technology was sufficiently far advanced to make that a viable option.

But Intelligence was frequently wrong, and even more often confused by the avalanche of raw facts it had to evaluate - the 'noise' in its information circuits. It had done a remarkable job on Tsien, considering the shortness of time, but Floyd wished that the material sent to him had been more carefully filtered. Some of it was obvious junk, of no possible connection with the mission.

Nevertheless, when you did not know what you were looking for, it was important to avoid all prejudices and preconceptions; something that at first sight seemed irrelevant, or even nonsensical, might turn out to be a vital clue.

With a sigh, Floyd started once more to skim the five hundred pages of data, keeping his mind as blankly receptive as possible while diagrams, charts, photographs - some so smudgy that they could represent almost anything - news items, lists of delegates to scientific conferences, titles of technical publications, and even commercial documents scrolled swiftly down the high-resolution screen. A very efficient industrial espionage system had obviously been extremely busy; who would have thought that so many Japanese holomemory modules or Swiss gas-flow microcontrollers or German radiation detectors could have been traced to a destination in the dried lake bed of Lop Nor - the first milepost on their way to Jupiter?

Some of the items must have been included by accident; they could not possibly relate to the mission. If the Chinese had placed a secret order for one thousand infrared sensors through a dummy corporation in Singapore, that was only the concern of the military; it seemed highly unlikely that Tsien expected to be chased by heat-seeking missiles. And this one was really funny - specialized surveying and prospecting equipment from Glacier Geophysics, Inc., of Anchorage, Alaska. What lamebrain imagined that a deep-space expedition would have any need - the smile froze on Floyd's lips; he felt the skin crawl on the back of his neck. My God - they wouldn't dare! But they had already dared greatly; and now, at last, everything made sense.

He flashed back to the photos and conjectured plans of the Chinese ship. Yes, it was just conceivable - those flutings at the rear, alongside the drive deflection electrodes, would be about the right size.

Floyd called the bridge. 'Vasili.' he said, 'have you worked out their orbit yet?'

'Yes, I have,' the navigator replied, in a curiously subdued voice. Floyd could tell at once that something had turned up. He took a long shot.

'They're making a rendezvous with Europa, aren't they?'

There was an explosive gasp of disbelief from the other end.

'Chyort voz'mi! How did you know?'

'I didn't - I've just guessed it.'

'There can't be any mistake - I've checked the figures to six places. The braking manoeuvre worked out exactly as they intended. They're right on course for Europa - it couldn't have happened by chance. They'll be there in seventeen hours.'

'And go into orbit.'

'Perhaps; it wouldn't take much propellant. But what would be the point?'

'I'll risk another guess. They'll do a quick survey - and then they'll land.'

'You're crazy - or do you know something we don't?'

'No - it's just a matter of simple deduction. You're going to start kicking yourself for missing the obvious.'

'Okay, Sherlock, why should anyone want to land on Europa? What's there, for heaven's sake?'

Floyd was enjoying his little moment of triumph. Of course, he might still be completely wrong.

'What's on Europa? Only the most valuable substance in the Universe.'

He had ove