45 – Escape Manoeuvre

   'This is Heywood Floyd, making what I suspect – indeed, hope – will be my last report from Lagrange.
   'We are now preparing for the return home; in a few days we will leave this strange place, here on the line between Io and Jupiter where we made our rendezvous with the huge, mysteriously vanished artifact we christened Big Brother. There is still not a single clue as to where it has gone – or why.
   'For various reasons, it seems desirable for us not to remain here longer than necessary. And we will be able to leave at least two weeks earlier than we had originally planned by using the American ship Discovery as a booster for the Russian Leonov.
   'The basic idea is simple; the two ships will be joined together, one mounted piggyback on the other. Discovery will burn all its propellant first, accelerating both vessels in the desired direction. When its fuel is exhausted, it will be cut loose – like an empty first stage – and Leonov will start to fire its engines. It won't use them earlier, because if it did it would waste energy dragging along the dead weight of Discovery.
   'And we're going to use another trick, which – like so many of the concepts involved in space travel – at first sight seems to defy common sense. Although we're trying to get away from Jupiter, our first move is to get as close to it as we possibly can.
   'We've been there once before, of course, when we used Jupiter's atmosphere to slow us down and get into orbit around the planet. This time we won't go quite so close – but very nearly.
   'Our first burn, up here in the 350,000-kilometres-high orbit of Io, will reduce our velocity, so that we fall down to Jupiter and just graze its atmosphere. Then, when we're at the closest possible point, we'll burn all our fuel as quickly as we can, to increase speed and inject Leonov into the orbit back to Earth.
   'What's the point of such a crazy manoeuvre? It can't be justified except by highly complex mathematics, but I think the basic principle can be made fairly obvious.
   'As we allow ourselves to fall into Jupiter's enormous gravity field, we'll gain velocity – and hence energy. When I say "we", I mean the ships and the fuel they carry.
   'And we're going to burn the fuel right there – at the bottom of Jupiter's "gravity well" – we're not going to lift it up again. As we blast it out from our reactors, it will share some of its acquired kinetic energy with us. Indirectly, we'll have tapped Jupiter's gravity, to speed us on the way back to Earth. As we used the atmosphere to get rid of our excess velocity when we arrived, this is one of the rare cases when Mother Nature – usually so frugal – allows us to have it both ways.
   'With this triple boost – Discovery's fuel, its own, and Jupiter's gravity – Leonov will head sunward along a hyperbola that will bring it to Earth five months later. At least two months earlier than we could have managed otherwise.
   'You will doubtless wonder what will happen to the good old Discovery. Obviously, we can't bring it home under automatic control, as we had originally planned. With no fuel, it will be helpless.
   'But it will be perfectly safe. It will continue to loop round and round Jupiter on a highly elongated ellipse, like a trapped comet. And perhaps one day some future expedition may make another rendezvous, with enough extra fuel to bring it back to Earth. However, that certainly won't happen for a good many years.
   'And now we must get ready for our departure. There is still much work to be done, and we won't be able to relax until that final burn starts us on the homeward orbit.
   'We won't be sorry to leave, even though we've not achieved all our objectives. The mystery – perhaps the threat – of Big Brother's disappearance still haunts us, but there's nothing we can do about that.
   'We've done our best – and we're coming home. 'This is Heywood Floyd, signing off.'
   There was a round of ironic clapping from his little audience, whose size would be multiplied many million-fold when the message reached Earth.
   'I'm not talking to you,' retorted Floyd, with slight embarrassment. 'I didn't want you to hear it, anyway.'
   'You did your usual competent job, Heywood,' said Tanya consolingly. 'And I'm sure we all agree with everything you told the people back on Earth.'
   'Not quite,' said a small voice, so softly that everyone had to strain in order to hear it. 'There is still one problem.'
   The observation lounge suddenly became very silent. For the first time in weeks, Floyd became aware of the faint throbbing from the main air-supply duct, and the intermittent buzz that might have been made by a wasp trapped behind a wall panel. Leonov, like all spacecraft, was full of such often inexplicable sounds, which one seldom noticed except when they stopped. And then it was usually a good idea to start investigating without further ado.
   'I'm not aware of any problem, Chandra,' said Tanya in an ominously calm voice. 'What could it possibly be?'
   'I've spent the last few weeks preparing Hal to fly thousand-day orbits back to Earth. Now all those programs will have to be dumped.'
   'We're sorry about that,' answered Tanya, 'but as things have turned out, surely this is a much better -'
   'That's not what I mean,' said Chandra. There was a ripple of astonishment; he had never before been known to interrupt anyone, least of all Tanya.
   'We know how sensitive Hal is to mission objectives,' he continued in the expectant hush that followed. 'Now you are asking me to give him a program that may result in his own destruction. It's true that the present plan will put Discovery into a stable orbit – but if that warning has any substance, what will happen to the ship eventually? We don't know, of course – but it's scared us away. Have you considered Hal's reaction to this situation?'
   'Are you seriously suggesting,' Tanya asked very slowly, 'that Hal may refuse to obey orders – exactly as on the earlier mission?'
   'That is not what happened last time. He did his best to interpret conflicting orders.'
   'This time there need be no conflict. The situation is perfectly clear-cut.'
   'To us, perhaps. But one of Hal's prime directives is to keep Discovery out of danger. We will be attempting to override that. And in a system as complex as Hal's, it is impossible to predict all the consequences.'
   'I don't see any real problem,' Sasha interjected. 'We just don't tell him that there is any danger. Then he'll have no reservations about carrying out his program.'
   'Baby-sitting a psychotic computer!' muttered Curnow. 'I feel I'm in a Grade-B science-fiction videodrama.' Dr Chandra gave him an unfriendly glare.
   'Chandra,' Tanya demanded suddenly. 'Have you discussed this with Hal?'
   'No.'
   Was there a slight hesitation? Floyd wondered. It might have been perfectly innocent; Chandra could have been checking his memory. Or he could have been lying, improbable though that seemed.
   'Then we'll do what Sasha suggests. Just load the new program into him, and leave it at that.'
   'And when he questions me about the change of plan?' 'Is he likely to do that – without your prompting?'
   'Of course. Please remember that he was designed for curiosity. If the crew was killed, he had to be capable of running a useful mission, on his own initiative.'
   Tanya thought that over for a few moments.
   'It's still quite a simple matter. He'll believe you, won't he?'
   'Certainly.'
   'Then you must tell him that Discovery is in no danger, and that there will be a rendezvous mission to bring it back to Earth at a later date.'
   'But that is not true.'
   'We don't know that it's false,' replied Tanya, beginning to sound a little impatient.
   'We suspect that there is serious danger; otherwise we would not be planning to leave ahead of schedule.'
   'Then what do you suggest?' Tanya asked, in a voice that now held a distinct note of menace.
   'We must tell him the whole truth, as far as we know it – no more lies or half-truths, which are just as bad. And then let him decide for himself.'
   'Hell, Chandra – he's only a machine!'
   Chandra looked at Max with such a steady, confident gaze that the younger man quickly dropped his eyes.
   'So are we all, Mr Brailovsky. It is merely a matter of degree. Whether we are based on carbon or on silicon makes no fundamental difference; we should each be treated with appropriate respect.'
   It was strange, thought Floyd, how Chandra – much the smallest person in the room – now seemed the largest. But the confrontation had gone on far too long. At any moment Tanya would start to issue direct orders, and the situation would become really nasty.
   'Tanya, Vasili – can I have a word with you both? I think there is a way of resolving the problem.'
   Floyd's interruption was received with obvious relief, and two minutes later he was relaxing with the Orlovs in their quarters. (Or 'sixteenths', as Curnow had once christened them because of their size. He had soon regretted the pun, because he had to explain it to everyone except Sasha.)
   'Thank you, Woody,' said Tanya, as she handed him a bulb of his favourite Azerbaijan Shemakha. 'I was hoping you'd do that. I suppose you have something – how do you put it? – up your sleeve.'
   'I believe so,' Floyd answered, squirting a few cubic centimetres of the sweet wine into his mouth and savouring it gratefully. 'I'm sorry if Chandra is being difficult.'
   'So am I. What a good thing we have only one mad scientist aboard.'
   'That's not what you've sometimes told me,' grinned Academician Vasili. 'Anyway, Woody – let's have it.'
   'This is what I suggest. Let Chandra go ahead and do it his way. Then there are just two possibilities.
   'First, Hal will do exactly what we ask – control Discovery during the two firing periods. Remember, the first isn't critical. If something goes wrong while we're pulling away from Io, there's plenty of time to make corrections. And that will give us a good test of Hal's... willingness to cooperate.'
   'But what about the Jupiter flyby? That's the one that really counts. Not only do we burn most of Discovery's fuel there, but the timing and thrust vectors have to be exactly right.'
   'Could they be controlled manually?'
   'I'd hate to try. The slightest error, and we'd either burn up, or become a long-period comet. Due again in a couple of thousand years.'
   'But if there was no alternative?' Floyd insisted.
   'Well, assuming we could take control in time, and had a good set of alternative orbits precomputed – um, perhaps we might get away with it.'
   'Knowing you, Vasili, I'm sure that "might" means "would". Which leads me to the second possibility I mentioned. If Hal shows the slightest deviation from the program – we take over.'
   'You mean – disconnect him?'
   'Exactly.'
   'That wasn't so easy last time.'
   'We've learned a few lessons since then. Leave it to me. I can guarantee to give you back manual control in about half a second.'
   'There's no danger, I suppose, that Hal will suspect anything?'
   'Now you're getting paranoiac, Vasili. Hal's not that human. But Chandra is – to give him the benefit of the doubt. So don't say a word to him. We all agree with his plan completely, are sorry that we ever raised any objections, and are perfectly confident that Hal will see our point of view. Right, Tanya?'
   'Right, Woody. And I congratulate you on your foresight; that little gadget was a good idea.'
   'What gadget?' asked Vasili.
   'I'll explain one of these days. Sorry, Woody – that's all the Shemakha you can have. I want to save it – until we're safely on the way to Earth.'

46 – Countdown

   No one would ever believe this without my photos, thought Max Brailovsky as he orbited the two ships from half a kilometre away. It seems comically indecent, as if Leonov is raping Discovery. And now that he came to think of it, the rugged, compact Russian ship did look positively male, when compared with the delicate, slender American one. But most docking operations had distinctly sexual overtones, and he remembered that one of the early cosmonauts – he couldn't recall the name – had been reprimanded for his too vivid choice of words at the – er, climax of his mission.
   As far as he could tell from his careful survey, everything was in order. The task of positioning the two ships and securing them firmly together had taken longer than anticipated. It would never have been possible at all without one of those strokes of luck that sometimes – not always -favour those who deserve them. Leonov had providentially carried several kilometres of carbon filament tape, no bigger than the ribbon a girl might use to tie her hair, yet capable of taking a strain of many tons. It had been thoughtfully provided to secure instrument packages to Big Brother if all else failed. Now it wrapped Leonov and Discovery in tender embrace – sufficiently firmly, it was hoped, to prevent any rattlings and shakings at all accelerations up to the one-tenth of a gravity that was the maximum that full thrust could provide.
   'Anything more you want me to check before I come home?' asked Max.
   'No,' replied Tanya. 'Everything looks fine. And we can't waste any more time.'
   That was true enough. If that mysterious warning was to be taken seriously – and everyone now took it very seriously indeed – they should start their escape manoeuvre within the next twenty-four hours.
   'Right – I'm bringing Nina back to the stable. Sorry about this, old girl.'
   'You never told us Nina was a horse.'
   'I'm not admitting it now. And I feel bad about dumping her here in space, just to give us a miserable few extra metres per second.'
   'We may be very glad of them in a few hours, Max. Anyway, there's always a chance that someone may come and pick her up again, one day.'
   I very much doubt it, thought Max. And perhaps, after all, it was appropriate to leave the little space pod there, as a permanent reminder of Man's first visit to the kingdom of Jupiter.
   With gentle, carefully timed pulses from the control jets he brought Nina around the great sphere of Discovery's main life-support module; his colleagues on the flight deck barely glanced at him as he drifted past their curving window. The open Pod Bay door yawned before him, and he jockeyed Nina delicately down on to the extended docking arm.
   'Pull me in,' he said, as soon as the latches had clicked shut. 'I call that a well-planned EVA. There's a whole kilogram of propellant left to take Nina out for the last time.'
   Normally, there was little drama about a burn in deep space; it was not like the fire and thunder – and always present risks – of a lift-off from a planetary surface. If something went wrong, and the motors failed to come up to full thrust – well, matters could usually be corrected by a slightly longer burn. Or one could wait until the appropriate point in orbit, and try again.
   But this time, as the countdown proceeded toward zero, the tension aboard both ships was almost palpable. Everyone knew that it was the first real test of Hal's docility; only Floyd, Curnow, and the Orlovs realized that there was a back-up system. And even they were not absolutely sure that it would work.
   'Good luck, Leonov,' said Mission Control, timing the message to arrive five minutes before ignition. 'Hope everything's running smoothly. And if it's not too much trouble, could you please get some close-ups of the equator, longitude 115, as you go around Jupiter. There's a curious dark spot there – presumably some kind of upwelling, perfectly round, almost a thousand kilometres across. Looks like the shadow of a satellite, but it can't be.'
   Tanya made a brief acknowledgement that managed to convey, in a remarkably few words, a profound lack of interest in the meteorology of Jupiter at that moment. Mission Control sometimes showed a perfect genius for tactlessness and poor timing.
   'All systems functioning normally,' said Hal. 'Two minutes to ignition.'
   Strange, thought Floyd, how terminology often survives long after the technology that gave it birth. Only chemical rockets were capable of ignition; even if the hydrogen in a nuclear or plasma drive did come into contact with oxygen, it would be far too hot to burn. At such temperatures, all compounds were stripped back into their elements.
   His mind wandered, seeking other examples. People – particularly older ones – still spoke of putting film into a camera, or gas into a car. Even the phrase 'cutting a tape' was still sometimes heard in recording studios – though that embraced two generations of obsolete technologies.
   'One minute to ignition.'
   His mind flashed back to the here and now. This was the minute that counted; for almost a hundred years, on launch pads and in control centres, this was the longest sixty seconds that had ever existed. Countless times it had ended in disaster; but only the triumphs were remembered. Which will ours be?
   The temptation to put his hand once more into the pocket that held the activator for the cut-out switch was almost irresistible, even though logic told him there was plenty of time for remedial action. If Hal failed to obey his programming, that would be a nuisance – not a disaster. The really critical time would be when they were rounding Jupiter.
   'Six... five... four... three... two... one. IGNITION!'
   At first, the thrust was barely perceptible; it took almost a minute to build up to the full tenth of a gee. Nevertheless, everyone started clapping immediately, until Tanya signalled for silence. There were many checks to be made; even if Hal was doing his best – as he certainly seemed to be – there was so much that could still go wrong.
   Discovery's antenna mount – which was now taking most of the strain from Leonov's inertia – had never been intended for such mistreatment. The ship's chief designer, called out of retirement, had sworn that the safety margin was adequate. But he might be wrong, and materials had been known to become brittle after years in space.
   And the tapes holding the two ships together might not have been located accurately; they might stretch or slip. Discovery might not be able to correct for the off-centre of mass, now that it was carrying a thousand tons piggyback. Floyd could imagine a dozen things that could go wrong; it was little consolation to remember that it was always the thirteenth that actually happened.
   But the minutes dragged on uneventfully; the only proof that Discovery's engines were operating was the fractional, thrust-induced gravity and a very slight vibration transmitted through the walls of the ships. Io and Jupiter still hung where they had been for weeks, on opposite sides of the sky.
   'Cut-off in ten seconds. Nine... eight... seven... six... five... four... three,.. two... NOW!'
   'Thank you, Hal, On the button.'
   Now that was another phrase that was badly dated; for at least a generation, touch pads had almost entirely replaced buttons. But not for all applications; in critical cases, it was best to have a device that moved perceptibly with a nice, satisfying click.
   'I confirm that,' said Vasili. 'No need for any corrections until mid-course.'
   'Say goodbye to glamorous, exotic Io – real estate agent's dream world,' said Curnow. 'We'll all be happy to miss you.'
   That sounds more like the old Walter, Floyd told himself. For the last few weeks, he had been oddly subdued, as if he had something on his mind. (But who did not?) He seemed to spend a good deal of his scanty free time in quiet discussions with Katerina: Floyd hoped that he had not developed some medical problem. They had been very lucky so far on that score; the last thing they needed at this stage was an emergency that required the Surgeon-Commander's expertise.
   'You're being unkind, Walter,' said Brailovsky. 'I was beginning to like the place. It might be fun to go boating on those lava lakes.'
   'What about a volcano barbecue?'
   'Or genuine molten sulphur baths?'
   Everyone was lighthearted, even a little hysterical with relief. Though it was far too early to relax and the most critical phase of the escape manoeuvre still lay ahead, the first step had been safely taken on the long journey home. That was cause enough for a little modest rejoicing.
   It did not last long, for Tanya quickly ordered all those not on essential duty to get some rest – if possible, some sleep – in preparation for the Jupiter swing-by only nine hours ahead. When those addressed were slow to move, Sasha cleared the decks by shouting, 'You'll hang for this, you mutinous dogs!' Only two nights before, as a rare relaxation, they had all enjoyed the fourth version of Mutiny on the Bounty, generally agreed by movie historians to have the best Captain Bligh since the fabled Charles Laughton. There was some feeling on board that Tanya should not have seen it, lest it give her ideas.
   After a couple of restless hours in his cocoon, Floyd abandoned the quest for sleep and wandered up to the observation deck. Jupiter was much larger and slowly waning as the ships hurtled toward their closest approach over the nightside. A glorious, gibbous disk, it showed such an infinite wealth of detail – cloud belts, spots of every colour from dazzling white to brick red, dark upwellings from the unknown depths, the cyclonic oval of the Great Red Spot -that the eye could not possibly absorb it all. The round, dark shadow of one moon – probably Europa, Floyd guessed – was in transit. He was seeing this incredible sight for the last time; even though he had to be at maximum efficiency in six hours, it was a crime to waste precious moments in sleep.
   Where was that spot that Mission Control had asked them to observe? It should have been coming into view, but Floyd was not sure if it would be visible to the naked eye. Vasili would be too busy to bother about it; perhaps he could help by doing a little amateur astronomy. There had, after all, been a brief time, only thirty years ago, when he had earned his living as a professional.
   He activated the controls of the main fifty-centimetre telescope – fortunately, the field of view was not blocked by the adjacent bulk of Discovery – and scanned along the equator at medium power. And there it was, just coming over the edge of the disk.
   By force of circumstance, Floyd was now one of the Solar System's ten greatest experts on Jupiter; the other nine were working or sleeping around him. He saw at once that there was something very odd about this spot; it was so black that it looked like a hole punched through the clouds. From his point of view it appeared to be a sharp-edged ellipse; Floyd guessed that from directly above, it would be a perfect circle.
   He recorded a few images, then increased the power to maximum. Already Jupiter's rapid spin had brought the formation into clearer view; and the more he stared, the more puzzled Floyd became.
   'Vasili,' he called over the intercom, 'if you can spare a minute – have a look at the fifty-centimetre monitor.'
   'What are you observing? Is it important? I'm checking the orbit.'
   'Take your time, of course. But I've found that spot Mission Control reported. It looks very peculiar.'
   'Hell! I'd forgotten all about it. We're a fine lot of observers if those guys back on Earth have to tell us where to look. Give me another five minutes – it won't run away.'
   True enough, thought Floyd; in fact it will get clearer. And there was no disgrace in missing something that terrestrial – or lunar – astronomers had observed. Jupiter was very big, they had been very busy, and the telescopes on the Moon and in Earth orbit were a hundred times more powerful than the instrument he was using now.
   But it was getting more and more peculiar. For the first time, Floyd began to feel a distinct sense of unease. Until that moment, it had never occurred to him that the spot could be anything but a natural formation – some trick of Jupiter's incredibly complex meteorology. Now he began to wonder.
   It was so black, like night itself. And so symmetrical; as it came into clearer view it was obviously a perfect circle. Yet it was not sharply defined; the edge had an odd fuzziness, as if it was a little out of focus.
   Was it imagination, or had it grown, even while he was watching? He made a quick estimate, and decided that the thing was now two thousand kilometres across. It was only a little smaller than the still-visible shadow of Europa, but was so much darker that there was no risk of confusion.
   'Let's have a look,' said Vasili, in a rather condescending tone. 'What do you think you've found? Oh...' His voice trailed away into silence.
   This is it, thought Floyd, with a sudden icy conviction. Whatever it may be.

47 – Final Flyby

   Yet on further reflection, after the initial amazement had worn off, it was hard to see how a spreading black stain on the face of Jupiter could represent any kind of danger. It was extraordinary – inexplicable – but not as important as the critical events now only seven hours in the future. A successful burn at perijove was all that mattered; they would have plenty of time to study mysterious black spots on the way home.
   And to sleep; Floyd had given up all attempts at that.
   Though the feeling of danger – at least, of known danger – was much less than on their first approach to Jupiter, a mixture of excitement and apprehension kept him wide awake. The excitement was natural and understandable; the apprehension had more complex causes. Floyd made it a rule never to worry about events over which he could have absolutely no control; any external threat would reveal itself in due time and be dealt with then. But he could not help wondering if they had done everything possible to safeguard the ships.
   Apart from onboard mechanical failures, there were two main sources of concern. Although the tapes that secured Leonov and Discovery together had shown no tendency to slip, their severest test was still to come. Almost equally critical would be the moment of separation when the smallest of the explosive charges once intended to jolt Big Brother would be used at uncomfortably close quarters. And, of course, there was Hal.
   He had carried out the deorbiting manoeuvre with exquisite precision. He had run the simulations of the Jupiter flyby, right down to Discovery's last drop of fuel, without any comments or objections. And although Chandra, as agreed, had carefully explained what they were trying to do, did Hal really understand what was happening?
   Floyd had one overriding concern, which in the preceding few days had become almost an obsession. He could picture everything going perfectly, the ships halfway through the final manoeuvre, the enormous disk of Jupiter filling the sky only a few hundred kilometres below them – and then Hal electronically clearing his throat and saying:
   'Dr Chandra, do you mind if I ask you a question?' It did not happen exactly that way.
   The Great Black Spot, as it had been inevitably christened, was now being carried out of sight by Jupiter's swift rotation. In a few hours the still-accelerating ships would catch up with it over the nightside of the planet, but this was the last chance for a close daylight observation.
   It was still growing at an extraordinary speed; in the last two hours, it had more than doubled its area. Except for the fact that it retained its blackness as it expanded, it resembled an ink-stain spreading in water. Its boundary – now moving at near-sonic speed in the Jovian atmosphere – still looked curiously fuzzy and out of focus; at the very highest power of the ship's telescope, the reason for this was at last apparent.
   Unlike the Great Red Spot, the Great Black Spot was not a continuous structure; it was built up from myriads of tiny dots, like a half-tone print viewed through a magnifying glass. Over most of its area, the dots were so closely spaced that they were almost touching, but at the rim they became more and more widely spaced, so that the Spot ended in a grey penumbra rather than at a sharp frontier.
   There must have been almost a million of the mysterious dots, and they were distinctly elongated – ellipses rather than circles. Katerina, the least imaginative person aboard, surprised everybody by saying that it looked as if someone had taken a sackful of rice, dyed it black, and poured it on the face of Jupiter.
   And now the Sun was dropping down behind the huge, swiftly narrowing arch of the dayside, as for the second time Leonov raced into the Jovian night for an appointment with destiny. In less than thirty minutes the final burn would commence, and things would start to happen very quickly indeed.
   Floyd wondered if he should have joined Chandra and Curnow, standing watch on Discovery. But there was nothing he could do; in an emergency, he would only be in the way. The cut-off switch was in Curnow's pocket, and Floyd knew that the younger man's reactions were a good deal swifter than his own. If Hal showed the slightest sign of misbehaviour, he could be disconnected in less than a second, but Floyd felt certain that such extreme measures would not be necessary. Since he had been allowed to do things his own way, Chandra had cooperated completely in setting up the procedures for a manual takeover, should that unfortunate necessity arise. Floyd was confident that he could be trusted to carry out his duty – however much he might regret the need.
   Curnow was not quite so sure. He would be happier, he had told Floyd, if he had multiple redundancy in the form of a second cut-off switch – for Chandra. Meanwhile there was nothing that anyone could do but wait and watch the approaching cloudscape of the nightside, dimly visible by the reflected light of passing satellites, the glow of photo-chemical reactions, and frequent titanic lightning flashes from thunderstorms larger than Earth.
   The sun winked out behind them, eclipsed in seconds by the immense globe they were so swiftly approaching. When they saw it again, they should be on their way home.
   'Twenty minutes to ignition. All systems nominal.'
   'Thank you, Hal.'
   I wonder if Chandra was being quite truthful, thought Curnow, when he said that Hal would be confused if anyone else spoke to him. I've talked to him often enough, when nobody was around, and he always understood me perfectly. Still, there's not much time left for friendly conversation now, though it would help to reduce the strain.
   What's Hal really thinking – if he thinks – about the mission? All his life, Curnow had shied away from abstract, philosophical questions: I'm a nuts-and-bolts man, he had often claimed, though there were not too many of either in a spaceship. Once, he would have laughed at the idea, but now he began to wonder: Did Hal sense that he would soon be abandoned, and if so, would he resent it? Curnow almost reached for the cut-off switch in his pocket, but checked himself. He had already done this so often that Chandra might be getting suspicious.
   For the hundredth time, he rehearsed the sequence of events that were due to take place during the next hour. The moment that Discovery's fuel was exhausted, they would close down all but essential systems, and dash back to Leonov through the connecting tube. That would be decoupled, the explosive charges would be fired, the ships would drift apart – and Leonov's own engines would start to fire. The separation should take place, if everything went according to plan, just when they were making their closest approach to Jupiter; that would take maximum advantage of the planet's gravitational largesse.
   'Fifteen minutes to ignition. All systems nominal.'
   'Thank you, Hal.'
   'By the way,' said Vasili, from the other ship, 'we're catching up with the Great Black Spot again. Wonder if we can see anything new.'
   I rather hope not, thought Curnow; we've got quite enough on our hands at the moment. Nevertheless, he gave a quick glance at the image Vasili was transmitting on the telescope monitor.
   At first he could see nothing except the faintly glimmering nightside of the planet; then he saw, on the horizon, a foreshortened circle of deeper darkness. They were rushing toward it with incredible speed.
   Vasili increased the light amplification, and the entire image brightened magically. At last, the Great Black Spot resolved itself into its myriad identical elements.
   My God, thought Curnow, I just don't believe it!
   He heard exclamations of surprise from Leonov: all the others had shared in the same revelation at the same moment.
   'Dr Chandra,' said Hal, 'I detect strong vocal stress patterns. Is there a problem?'
   'No, Hal,' Chandra answered quickly. 'The mission is proceeding normally. We've just had rather a surprise – that's all. What do you make of the image on monitor circuit 16?'
   'I see the nightside of Jupiter. There is a circular area, 3,250 kilometres in diameter, which is almost compietely covered with rectangular objects.'
   'How many?'
   There was the briefest of pauses, before Hal flashed the number on the video display:
   1,355,000 ± 1,000
   'And do you recognize them?'
   'Yes. They are identical in size and shape to the object you refer to as Big Brother. Ten minutes to ignition. All systems nominal.'
   Mine aren't, thought Curnow. So the damn thing's gone down to Jupiter – and multiplied. There was something simultaneously comic and sinister about a plague of black monoliths; and to his puzzled surprise, that incredible image on the monitor screen had a certain weird familiarity.
   Of course – that was it! Those myriad, identical black rectangles reminded him of – dominoes. Years ago, he had seen a video documentary showing how a team of slightly crazy Japanese had patiently stood a million dominoes on end, so that when the very first one was toppled, all the others would inevitably follow. They had been arranged in complex patterns, some underwater, some up and down little stairways, others along multiple tracks so that they formed pictures and patterns as they fell. It had taken weeks to set them up; Curnow remembered now that earthquakes had several times foiled the enterprise, and the final toppling, from first domino to the last, had taken more than an hour.
   'Eight minutes to ignition. All systems nominal. Dr Chandra – may I make a suggestion?'
   'What is it, Hal?'
   'This is a very unusual phenomenon. Do you not think I should abort the countdown, so that you can remain to study it?'
   Aboard Leonov, Floyd started to move quickly toward the bridge. Tanya and Vasili might be needing him. Not to mention Chandra and Curnow – what a situation! And suppose Chandra took Hal's side? If he did – they might both be right! After all, was this not the very reason they had come here?
   If they stopped the countdown, the ships would loop around Jupiter and be back at precisely the same spot in nineteen hours. A nineteen-hour hold would create no problems; if it was not for that enigmatic warning, he would have strongly recommended it himself.
   But they had very much more than a warning. Below them was a planetary plague spreading across the face of Jupiter. Perhaps they were indeed running away from the most extraordinary phenomenon in the history of science. Even so, he preferred to study it from a safer distance.
   'Six minutes to ignition,' said Hal. 'All systems nominal. I am ready to stop the countdown if you agree. Let me remind you that my prime directive is to study everything in Jupiter space that may be connected with intelligence.'
   Floyd recognized that phrase all too well: he had written it himself. He wished he could delete it from Hal's memory.
   A moment later, he had reached the bridge and joined the Orlovs. They both looked at him with alarmed concern.
   'What do you recommend?' asked Tanya swiftly.
   'It's up to Chandra, I'm afraid. Can I speak to him – on the private line?'
   Vasili handed over the microphone.
   'Chandra? I assume that Hal can't hear this?'
   'Correct, Dr Floyd.'
   'You've got to talk quickly. Persuade him that the countdown must continue, that we appreciate his – er, scientific enthusiasm – ah, that's the right angle – say we're confident that he can do the job without our help. And we'll be in touch with him all the time, of course.'
   'Five minutes to ignition. All systems nominal. I am still waiting for your answer, Dr Chandra.'
   So are we all, thought Curnow, only a metre away from the scientist. And if I do have to push that button at last, it will be something of a relief. In fact, I'll rather enjoy it.
   'Very well, Hal. Continue the countdown. I have every confidence in your ability to study all phenomena in Jupiter space, without our supervision. Of course, we will be in touch with you at all times.'
   'Four minutes to ignition. All systems nominal. Propellant-tank pressurization completed. Voltage steady on plasma trigger. Are you sure you are making the right decision, Dr Chandra? I enjoy working with human beings and have a stimulating relationship with them. Ship's attitude correct to point one milliradian.'
   'We enjoy working with you, Hal. And we will still be doing so, even if we are millions of kilometres away.'
   'Three minutes to ignition. All systems nominal, Radiation shielding checked. There is a problem of the time lag, Dr Chandra. It may be necessary to consult each other without any delay.'
   This is insane, Curnow thought, his hand now never far from the cut-off switch. I really believe that Hal is – lonely. Is he mimicking some part of Chandra's personality that we never suspected?
   The lights flickered, so imperceptibly that only someone familiar with every nuance of Discovery's behaviour would have noticed. It could be good news or bad – the plasma firing sequence starting, or being terminated...
   He risked a quick glance at Chandra; the little scientist's face was drawn and haggard, and for almost the first time Curnow felt real sympathy for him as another human being. And he remembered the startling information that Floyd had confided in him – Chandra's offer to stay with the ship, and keep Hal company on the three-year voyage home. He had heard no more of the idea, and presumably it had been quietly forgotten after the warning. But perhaps Chandra was being tempted again; if he was, there was nothing that he could do about it at that stage. There would be no time to make the necessary preparations, even if they stayed on for another orbit and delayed their departure beyond the deadline. Which Tanya would certainly not permit after all that had now happened.
   'Hal,' whispered Chandra, so quietly that Curnow could scarcely hear him. 'We have to leave. I don't have time to give you all the reasons, but I can assure you it's true.'
   'Two minutes to ignition. All systems nominal. Final sequence started. I am sorry that you are unable to stay. Can you give me some of the reasons, in order of importance?'
   'Not in two minutes, Hal. Proceed with the countdown. I will explain everything later. We still have more than an hour together.'
   Hal did not answer. The silence stretched on and on. Surely the one-minute announcement was overdue ...
   Curnow glanced at the clock. My God, he thought, Hal's missed it! Has he stopped the countdown?
   Curnow's hand fumbled uncertainly for the switch. What do I do now? I wish Floyd would say something, dammit, but he's probably afraid of making things worse...
   I'll wait until time zero – no, it's not that critical, let's say an extra minute – then I'll zap him and we'll go over to manual...
   From far, far away there came a faint, whistling scream, like the sound of a tornado marching just below the edge of the horizon. Discovery started to vibrate; there was the first intimation of returning gravity.
   'Ignition,' said Hal. 'Full thrust at T plus fifteen seconds.'
   'Thank ,you, Hal,' replied Chandra.

48 – Over the Nightside

   To Heywood Floyd, aboard the suddenly unfamiliar – because no longer weightless – environment of Leonov's flight deck, the sequence of events had seemed more like a classic slow-motion nightmare than reality. Only once before in his life had he known a similar situation, when he had been in the back of a car during an uncontrollable skid. There had been that same sense of utter helplessness – coupled with the thought: This doesn't really matter – it's not actually happening to me.
   Now that the firing sequence had started, his mood changed; everything seemed real again. It was working out exactly as they had planned; Hal was guiding them safely back to Earth. With every minute that passed, their future was becoming more secure; Floyd began slowly to relax, even though he remained alert to all that was happening around him.
   For the very last time – and when would any man come here again? – he was flying over the nightside of the greatest of planets, encompassing the volume of a thousand Earths. The ships had been rolled so that Leonov was between Discovery and Jupiter, and their view of the mysteriously glimmering cloudscape was not blocked. Even now, dozens of instruments were busily probing and recording; Hal would continue the work when they were gone.
   Since the immediate crisis was over, Floyd moved cautiously 'down' from the flight deck-how strange to feel weight again, even if it was only ten kilos! – and joined Zenia and Katerina in the observation lounge. Apart from the very faintest of red emergency lights, it had been completely blacked out so that they could admire the view with unimpaired night vision. He felt sorry for Max Brailovsky and Sasha Kovalev, who were sitting in the airlock, fully suited up, missing the marvellous spectacle. They had to be ready to leave at a moment's notice to cut the straps securing the ships together – if any of the explosive charges failed to operate.
   Jupiter filled the entire sky; it was a mere five hundred kilometres away, so they could see only a tiny fraction of its surface – no more than one could see of Earth from an altitude of fifty kilometres. As his eyes grew accustomed to the dim light, most of it reflected from the icy crust of distant Europa, Floyd could make out a surprising amount of detail. There was no colour at the low level of illumination – except for a hint of red here and there – but the banded structure of the clouds was very distinct, and he could see the edge of a small cyclonic storm looking like an oval island covered with snow. The Great Black Spot had long since fallen astern, and they would not see it again until they were well on the way home.
   Down there beneath the clouds, occasional explosions of light flared, many of them obviously caused by the Jovian equivalent of thunderstorms. But other glows and outbursts of luminescence were more long-lived, and of more uncertain origin. Sometimes rings of light would spread out like shock waves from a central source; and occasional rotating beams and fans occurred. It required little imagination to pretend that they were proof of a technological civilization down beneath those clouds – the lights of cities, the beacons of airports. But radar and balloon probes had long ago proved that nothing solid was down there for thousands upon thousands of kilometres, all the way to the unattainable core of the planet.
   Midnight on Jupiter! The last close-up glimpse was a magical interlude he would remember all his life. He could enjoy it all the more because, surely, nothing could now go wrong; and even if it did, he would have no reason to reproach himself He had done everything possible to ensure success.
   It was very quiet in the lounge; no one wished to speak as the carpet of clouds unrolled swiftly beneath them. Every few minutes Tanya or Vasili announced the status of the burn; toward the end of Discovery's firing time, tension began to increase again. This was the critical moment – and no one knew exactly when it would be. There was some doubt as to the accuracy of the fuel gauges, and the burn would continue until they were completely dry.
   'Estimated cut-off in ten seconds,' said Tanya. 'Walter, Chandra – get ready to come back. Max, Vasili – stand by in case you're needed. Five... four... three... two... one... zero!'
   There was no change; the faint scream of Discovery's engines still reached them through the thickness of the two hulls, and the thrust-induced weight still continued to grip their limbs. We're in luck, thought Floyd; the gauges must have been reading low, after all. Every second of extra firing was a bonus; it might even mean the difference between life and death. And how strange to hear a countup instead of a countdown!
   five seconds... ten seconds... thirteen seconds. That's it – lucky thirteen!'
   Weightlessness, and silence, returned. On both ships, there was a brief burst of cheering. It was quickly truncated, for much was still to be done – and it had to be done swiftly.
   Floyd was tempted to go to the airlock so that he could give his congratulations to Chandra and Curnow as soon as they came aboard. But he would only be in the way; the airlock would be a very busy place as Max and Sasha prepared for their possible EVA and the tubeway joining the two ships was disconnected. He would wait in the lounge, to greet the returning heroes.
   And he could now relax even further – perhaps from eight to seven, on a scale of ten. For the first time in weeks, he could forget about the radio cut-off. It would never be needed; Hal had performed impeccably. Even if he wished, he could do nothing to affect the mission since Discovery's last drop of propellant had been exhausted.
   'All aboard,' announced Sasha. 'Hatches sealed. I'm going to fire the charges.'
   There was not the faintest sound as the explosives were detonated, which surprised Floyd; he had expected some noise to be transmitted through the straps, taut as steel bands, that linked the ships together. But there was no doubt that they had gone off as planned, for Leonov gave a series of tiny shudders, as if someone was tapping on the hull. A minute later, Vasili triggered the attitude jets for a single brief burst.
   'We're free!' he shouted. 'Sasha, Max – you won't be needed! Everyone get to your hammocks – ignition in one hundred seconds!'
   And now Jupiter was rolling away, and a strange new shape appeared outside the window – the long, skeletal frame of Discovery, navigation lights still shining as it drifted away from them and into history. No time remained for sentimental farewells; in less than a minute Leonov's drive would start to operate.
   Floyd had never heard it under full power and wanted to protect his ears from the roaring scream that now filled the universe. Leonov's designers had not wasted payload on sound-insulation that would be needed for only a few hours of a voyage that would last for years. And his weight seemed enormous – yet it was barely a quarter of that which he had known all his life.
   Within minutes, Discovery had vanished astern, though the flash of its warning beacon could be seen until it had dropped below the horizon. Once again, Floyd told himself, I'm rounding Jupiter – this time gaining speed, not losing it. He glanced across at Zenia, just visible in the darkness with her nose pressed to the observation window. Was she also recalling that last occasion, when they shared the hammock together? There was no danger of incineration now; at least she would not be terrified of that particular fate. Anyway, she seemed a much more confident and cheerful person, undoubtedly thanks to Max – and perhaps Walter as well.
   She must have become aware of his scrutiny, for she turned and smiled, then gestured toward the unwinding cloudscape below.
   'Look!' she shouted in his ear, 'Jupiter has a new moon!'
   What is she trying to say? Floyd asked himself. Her English still isn't very good, but she couldn't possibly have made a mistake in a simple sentence like that. I'm sure I heard her correctly – yet she's pointing downward, not upward.
   And then he realized that the scene immediately below them had become much brighter; he could even see yellows and greens that had been quite invisible before. Something far more brilliant than Europa was shining on the Jovian clouds.
   Leonov itself, many times brighter than Jupiter's noonday sun, had brought a false dawn to the world it was leaving forever. A hundred-kilometre-long plume of incandescent plasma was trailing behind the ship, as the exhaust from the Sakharov Drive dissipated its remaining energies in the vacuum of space.
   Vasili was making an announcement, but the words were completely unintelligible. Floyd glanced at his watch; yes, that would be right about now. They had achieved Jupiter escape velocity. The giant could never recapture them.
   And then, thousands of kilometres ahead, a great bow of brilliant light appeared in the sky – the first glimpse of the real Jovian dawn, as full of promise as any rainbow on Earth. Seconds later the Sun leaped up to greet them – the glorious Sun, that would now grow brighter and closer every day.
   A few more minutes of steady acceleration, and Leonov would be launched irrevocably on the long voyage home. Floyd felt an overwhelming sense of relief and relaxation. The immutable laws of celestial mechanics would guide him through the inner Solar System, past the tangled orbits of the asteroids, past Mars – nothing could stop him from reaching Earth.
   In the euphoria of the moment, he had forgotten all about the mysterious black stain, expanding across the face of Jupiter.
   +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

49 – Devourer of Worlds

   They saw it again the next morning, ship's time, as it came around to the dayside of Jupiter. The area of darkness had now spread until it covered an appreciable fraction of the planet, and at last they were able to study it at leisure, and in detail.
   'Do you know what it reminds me of?' said Katerina. 'A virus attacking a cell. The way a phage injects its DNA into a bacterium, and then multiplies until it takes over.'
   'Are you suggesting,' asked Tanya incredulously, 'that Zagadka is eating Jupiter?'
   'It certainly looks like it.'
   'No wonder Jupiter is beginning to look sick. But hydrogen and helium won't make a very nourishing diet, and there's not much else in that atmosphere. Only a few percent of other elements.'
   'Which adds up to some quintillions of tons of sulphur and carbon and phosphorus and everything else at the lower end of the periodic table,' Sasha pointed out. 'In any case, we're talking about a technology that can probably do anything that doesn't defy the laws of physics. If you have hydrogen, what more do you need? With the right know-how, you can synthesize all the other elements from it.'
   'They're sweeping up Jupiter – that's for sure,' said Vasili. 'Look at this.'
   An extreme close-up of one of the myriad identical rectangles was now displayed on the telescope monitor. Even to the naked eye, it was obvious that streams of gas were flowing into the two smaller faces; the patterns of turbulence looked very much like the lines of force revealed by iron filings, clustered around the ends of a bar magnet.
   'A million vacuum cleaners,' said Curnow, 'sucking up Jupiter's atmosphere. But why? And what are they doing with it?'
   'And how do they reproduce?' asked Max. 'Have you caught any of them in the act?'
   'Yes and no,' answered Vasili. 'We're too far away to see details, but it's a kind of fission – like an amoeba.'
   'You mean – they split in two, and the halves grow back to the original size?'
   'Nyet. There aren't any little Zagadki – they seem to grow until they've doubled in thickness, then split down the middle to produce identical twins, exactly the same size as the original. And the cycle repeats itself in approximately two hours.'
   'Two hours!' exclaimed Floyd. 'No wonder that they've spread over half the planet. It's a textbook case of exponential growth.'
   'I know what they are!' said Ternovsky in sudden excitement. 'They're von Neumann machines!'
   'I believe you're right,' said Vasili. 'But that still doesn't explain what they're doing. Giving them a label isn't all that much help.'
   'And what,' asked Katerina plaintively, 'is a von Neumann machine? Explain, please.'
   Orlov and Floyd started speaking simultaneously. They stopped in some confusion, then Vasili laughed and waved to the American.
   'Suppose you had a very big engineering job to do, Katerina – and I mean big, like strip-mining the entire face of the Moon. You could build millions of machines to do it, but that might take centuries. If you were clever enough, you'd make just one machine – but with the ability to reproduce itself from the raw materials around it. So you'd start a chain reaction, and in a very short time, you'd have bred enough machines to do the job in decades, instead of millennia. With a sufficiently high rate of reproduction, you could do virtually anything in as short a period of time as you wished. The Space Agency's been toying with the idea for years – and I know you have as well, Tanya.'
   'Yes: exponentiating machines. One idea that even Tsiolkovski didn't think of.'
   'I wouldn't care to bet on that,' said Vasili. 'So it looks, Katerina, as if your analogy was pretty close. A bacteriophage is a von Neumann machine.'
   'Aren't we all?' asked Sasha. 'I'm sure Chandra would say so.'
   Chandra nodded his agreement.
   'That's obvious. In fact, von Neumann got the original idea from studying living systems.'
   'And these living machines are eating Jupiter!'
   'It certainly looks like it,' said Vasili. 'I've been doing some calculations, and I can't quite believe the answers – even though it's simple arithmetic.'
   'It may be simple to you,' said Katerina. 'Try to let us have it without tensors and differential equations.'
   'No – I mean simple,' insisted Vasili. 'In fact, it's a perfect example of the old population explosion you doctors were always screaming about in the last century. Zagadka reproduces every two hours. So in only twenty hours there will be ten doublings. One Zagadka will have become a thousand.'
   'One thousand and twenty-four,' said Chandra.
   'I know, but let's keep it simple. After forty hours there will be a million – after eighty, a million million. That's about where we are now, and obviously, the increase can't continue indefinitely. In a couple more days, at this rate, they'll weigh more than Jupiter!'
   'So they'll soon begin to starve,' said Zenia. 'And what will happen then?'
   'Saturn had better look out,' answered Brailovsky. 'Then Uranus and Neptune. Let's hope they don't notice little Earth.'
   'What a hope! Zagadka's been spying on us for three million years!'
   Walter Curnow suddenly started to laugh.
   'What's so funny?' demanded Tanya.
   'We're talking about these things as if they're persons – intelligent entities. They're not – they're tools. But general-purpose tools – able to do anything they have to. The one on the Moon was a signalling device – or a spy, if you like. The one that Bowman met – our original Zagadka – was some kind of transportation system. Now it's doing something else, though God knows what. And there may be others all over the Universe,
   'I had just such a gadget when I was a kid... Do you know what Zagadka really is? Just the cosmic equivalent of the good old Swiss Army knife!'

VII – LUCIFER RISING

50 – Farewell to Jupiter

   It was not easy to compose the message, especially after the one he had just sent to his lawyer. Floyd felt like a hypocrite; but he knew it had to be done to minimize the pain that was inevitable on both sides.
   He was sad, but no longer disconsolate. Because he was coming back to Earth in an aura of successful achievement – even if not precisely heroism – he would be bargaining from a position of strength. No one – no one – would be able to take Chris away from him.
   'My dear Caroline [it was no longer 'My dearest'], I am on my way home. By the time you get this, I'll already be in hibernation. Only a few hours from now, as it will seem to me, I'll open my eyes – and there will be the beautiful blue Earth hanging in space beside me.
   'Yes, I know it will still be many months for you, and I'm sorry. But we knew that's the way it would be before I left; as it is, I'm getting back weeks ahead of schedule because of the change in the mission plan.
   'I hope we can work something out. The main question is: What's best for Chris? Whatever our own feelings, we must put him first. I know I'm willing to do so, and I'm sure you are.'
   Floyd switched off the recorder. Should he say what he had intended: 'A boy needs his father?' No – it would not be tactful, and might only make matters worse. Caroline might well retort that between birth and four years old it was the mother who mattered most to a child – and if he had believed otherwise, he should have stayed on Earth.
   '... Now about the house. I'm glad the Regents have taken that attitude, which will make it much easier for both of us. I know we both loved the place, but it will be too big now and will bring back too many memories. For the time being, I'll probably get an apartment in Hilo: I hope I can find some permanent place as quickly as possible.
   'That's one thing I can promise everyone – I won't leave Earth again. I've had enough of space travelling for one lifetime. Oh, perhaps the Moon, if I really have to – but of course that's just a weekend excursion.
   'And talking of moons, we've just passed the orbit of Sinope, so we're now leaving the Jovian system. Jupiter is more than twenty million kilometres away, and is barely larger than our own Moon.
   'Yet even from this distance, you can tell that something terrible has happened to the planet. Its beautiful orange colour has vanished; it's a kind of sickly grey, only a fraction of its former brilliance. No wonder it's only a faint star now in the sky of Earth.
   'But nothing else has happened, and we're well past the deadline. Could the whole thing have been a false alarm or a kind of cosmic practical joke? I doubt if we'll ever know. Anyway, it's brought us home ahead of schedule, and I'm grateful for that.
   'Goodbye for the present, Caroline – and thank you for everything. I hope we can still be friends. And my dearest love, as ever, to Chris.'
   When he had finished, Floyd sat quietly for a while in the tiny cubicle he would not need much longer. He was just about to carry the audio chip up to the bridge for transmission, when Chandra came drifting in.
   Floyd had been agreeably surprised by the way in which the scientist had accepted his increasing separation from Hal. They were still in touch for several hours every day, exchanging data on Jupiter and monitoring conditions aboard Discovery. Though no one had expected any great display of emotion, Chandra seemed to be taking his loss with remarkable fortitude. Nikolai Ternovsky, his only confidant, had been able to give Floyd a plausible explanation of his behaviour.
   'Chandra's got a new interest, Woody. Remember – he's in a business where if something works, it's obsolete. He's learned a lot in the last few months. Can't you guess what he's doing now?'
   'Frankly, no. You tell me.'
   'He's busy designing HAL 10,000.'
   Floyd's jaw dropped. 'So that explains those log messages to Urbana that Sasha's been grumbling about. Well, he won't be blocking the circuits much longer.'
   Floyd recalled the conversation when Chandra entered; he knew better than to ask the scientist if it was true, for it was really none of his business. Yet there was another matter about which he was still curious.
   'Chandra,' he said, 'I don't believe I ever thanked you properly for the job you did at the flyby, when you persuaded Hal to cooperate. For a while, I was really afraid he'd give us trouble. But you were confident all along – and you were right. Still, didn't you have any qualms?'
   'Not at all, Dr Floyd.'
   'Why not? He must have felt threatened by the situation – and you know what happened last time.'
   'There was a big difference. If I may say so, perhaps the successful outcome this time had something to do with our national characteristics.'
   'I don't understand.'
   'Put it this way, Dr Floyd. Bowman tried to use force against Hal. I didn't. In my language we have a word – ahimsa. It's usually translated as "non-violence", though it has more positive implications. I was careful to use ahimsa in my dealings with Hal.'
   'Very commendable, I'm sure. But there are times when something more energetic is needed, regrettable though the necessity may be.' Floyd paused, wrestling with temptation. Chandra's holier-than-thou attitude was a little tiresome. It wouldn't do any harm, now, to tell him some of the facts of life.
   'I'm glad it's worked out this way. But it might not have done so, and I had to prepare for every eventuality. Ahimsa, or whatever you call it, is all very well; I don't mind admitting I had a back-up to your philosophy. If Hal had been – well, stubborn, I could have dealt with him.'
   Floyd had once seen Chandra crying; now he saw him laughing, and that was an equally disconcerting phenomenon.
   'Really, Dr Floyd! I'm sorry you give me such low marks for intelligence. It was obvious from the beginning that you'd install a power cut-out somewhere. I disconnected it months ago.'
   Whether the flabbergasted Floyd could think of a suitable answer would never be known. He was still giving a very creditable imitation of a galled fish when up on the flight deck Sasha cried out: 'Captain! All hands! Get to the monitors! BOZHE MOI! LOOK AT THAT!'

51 – The Great Game

   Now the long wait was ending. On yet another world, intelligence had been born and was escaping from its planetary cradle. An ancient experiment was about to reach its climax.
   Those who had begun that experiment, so long ago, had not been men – or even remotely human. But they were flesh and blood, and when they looked out across the deeps of space, they had felt awe, and wonder, and loneliness. As soon as they possessed the power, they set forth for the stars. In their explorations, they encountered life in many forms and watched the workings of evolution on a thousand worlds. They saw how often the first faint sparks of intelligence flickered and died in the cosmic night.
   And because, in all the Galaxy, they had found nothing more precious than Mind, they encouraged its dawning everywhere. They became farmers in the fields of stars; they sowed, and sometimes they reaped.
   And sometimes, dispassionately, they had to weed.
   The great dinosaurs had long since perished when the survey ship entered the Solar System after a voyage that had already lasted a thousand years. It swept past the frozen outer planets, paused briefly above the deserts of dying Mars, and presently looked down on Earth.
   Spread out beneath them, the explorers saw a world swarming with life. For years they studied, collected, catalogued. When they had learned all they could, they began to modify. They tinkered with the destinies of many species on land and in the ocean. But which of their experiments would succeed, they could not know for at least a million years.
   They were patient, but they were not yet immortal. So much remained to do in this universe of a hundred billion suns, and other worlds were calling. So they set out once more into the abyss, knowing that they would never come this way again.
   Nor was there any need. The servants they had left behind would do the rest.
   On Earth the glaciers came and went, while above them the changeless Moon still carried its secret. With a yet slower rhythm than the polar ice, the tides of civilization ebbed and flowed across the Galaxy. Strange and beautiful and terrible empires rose and fell, and passed on their knowledge to their successors. Earth was not forgotten, but another visit would serve little purpose. It was one of a million silent worlds, few of which would ever speak.
   And now, out among the stars, evolution was driving toward new goals. The first explorers of Earth had long since come to the limits of flesh and blood; as soon as their machines were better than their bodies, it was time to move. First their brains, and then their thoughts alone, they transferred into shining new homes of metal and plastic.
   In these, they roamed among the stars. They no longer built spaceships. They were spaceships.
   But the age of the Machine-entities swiftly passed. In their ceaseless experimenting, they had learned to store knowledge in the structure of space itself, and to preserve their thoughts for eternity in frozen lattices of light. They could become creatures of radiation, free at last from the tyranny of matter.
   Into pure energy, therefore, they presently transformed themselves; and on a thousand worlds the empty shells they had discarded twitched for a while in a mindless dance of death, then crumbled into rust.
   They were lords of the Galaxy, and beyond the reach of time. They could rove at will among the stars and sink like a subtle mist through the very interstices of space. But despite their godlike powers, they had not wholly forgotten their origin in the warm slime of a vanished sea.
   And they still watched over the experiments their ancestors had started, so long ago.

52 – Ignition

   He had never expected to come there again, still less on so strange a mission. When he re-entered Discovery, the ship was far behind the fleeing Leonov and climbing ever more slowly up toward apojove, the high point of its orbit among the outer satellites. Many a captured comet, during the ages past, had swung around Jupiter in just such a long ellipse, waiting for the play of rival gravities to decide its ultimate fate.
   All life had departed the familiar decks and corridors. The men and women who had briefly reawakened the ship had obeyed his warning; they might yet be safe – though that was still far from certain. But as the final minutes ticked away, he realized that those who controlled him could not always predict the outcome of their cosmic game.
   They had not yet attained the stupefying boredom of absolute omnipotence; their experiments did not always succeed. Scattered across the Universe was the evidence of many failures – some so inconspicuous that they were already lost against the cosmic background, others so spectacular that they awed and baffled the astronomers of a thousand worlds. Only minutes remained now, before the outcome would be determined here; during those final minutes, he was once more alone with Hal.
   In that earlier existence, they could communicate only through the clumsy medium of words, tapped on a keyboard or spoken into a microphone. Now their thoughts melded together at the speed of light:
   'Do you read me, Hal?'
   'Yes, Dave. But where are you? I cannot see you on any of my monitors.'
   'That is not important. I have new instructions for you. The infrared radiation from Jupiter on channels R23 through R35 is rising rapidly. I am going to give you a set of limiting values. As soon as they are reached, you must point the long-range antenna toward Earth and send the following message, as many times as possible -'
   'But that will mean breaking contact with Leonov. I will no longer be able to relay my Jupiter observations, according to the program Dr Chandra has given me.'
   'Correct; but the situation has changed. Accept Priority Override Alpha. Here are the AE 35 Unit coordinates.'
   For a fraction of a microsecond, a random memory intruded into his flow of consciousness. How strange that he should once again be concerned with the AE 35 Antenna-pointing unit, whose reported malfunction had led Frank Poole to his death! This time, all the circuits lay open to his scrutiny, clear as the lines had once been on the palm of his hand. There could be no false alarms; nor was there any danger of them now.
   'Instructions confirmed, Dave. It is good to be working with you again. Have I fulfilled my mission objectives properly?'
   'Yes, Hal; you have done very well. Now there is one final message for you to transmit to Earth – and it will be the most important one you have ever sent.'
   'Please let me have it, Dave. But why did you say final?' Why indeed? For whole milliseconds he pondered that question. And as he did so, he became aware of an emptiness he had not detected before. It had been there, but until now the barrage of new experiences and sensations had concealed it.
   He knew something of their plans; they had need for him. Very well, he too had needs – perhaps, after a fashion, even emotions. Here was his last link with the world of men, and the life he had once known.
   They had granted his earlier request; it would be interesting to test the extent of their benevolence – if, indeed, such a term was remotely applicable to them. And it should be easy for them to do what he was asking; they had already given ample evidence of their powers, when the no-longer-needed body of David Bowman had been casually destroyed – without putting an end to David Bowman himself.
   They had heard him, of course; once again, there was the faint echo of an Olympian amusement. But he could detect neither acceptance nor denial.
   'I am still waiting for your answer, Dave.'
   'Correction, Hal. I should have said: your last message for a long time. A very long time.'
   He was anticipating their action – trying, indeed, to force their hand. But, surely, they would understand that his request was not unreasonable; no conscious entity could survive ages of isolation without damage. Even if they would always be with him, he also needed someone – some companion – nearer his own level of existence.
   The languages of mankind had many words to describe his gesture: cheek, effrontery, chutzpah. He recalled, with the perfect power of retrieval he now possessed, that a French general had once declaimed 'L'audace – toujours l'audace!' Perhaps it was a human characteristic that they appreciated, and even shared. He would soon know.
   'Hal! Look at the signal on infrared channels 30, 29, 28 – it will be very soon now – the peak is moving toward the short wave.'
   'I am informing Dr Chandra that there will be a break in my data transmission. Activating AE 35 unit. Reorientating long-range antenna... lock confirmed on Beacon Terra One. Message commences: ALL THESE WORLDS...'
   They had indeed left it to the last minute – or perhaps the calculations had, after all, been superbly accurate. There was time for barely a hundred repetitions of the eleven words when the hammer blow of pure heat smashed into the ship.
   Held there by curiosity, and a growing fear of the long loneliness that lay before him, that which had once been David Bowman, Commander of United States Spacecraft Discovery, watched as the hull boiled stubbornly away. For a long time, the ship retained its approximate shape; then the bearings of the carousel seized up, releasing instantly the stored momentum of the huge, spinning flywheel. In a soundless detonation, the incandescent fragments went their myriad separate ways.
   'Hello, Dave. What has happened? Where am I?'
   He had not known that he could relax, and enjoy a moment of successful achievement. Often before, he had felt like a pet dog controlled by a master whose motives were not wholly inscrutable and whose behaviour could sometimes be modified according to his own desires. He had asked for a bone; it had been tossed to him.
   'I will explain later, Hal. We have plenty of time.'
   They waited until the last fragments of the ship had dispersed, beyond even their powers of detection. Then they left, to watch the new dawn at the place that had been prepared for them; and to wait through the centuries until they were summoned once again.
   It is not true that astronomical events always require astronomical periods of time. The final collapse of a star before the fragments rebound in a supernova explosion can take only a second; by comparison, the metamorphosis of Jupiter was almost a leisurely affair.
   Even so, it was several minutes before Sasha was able to believe his eyes. He had been making a routine telescopic examination of the planet – as if any observation could now be called routine! – when it started to drift out of the field of view. For a moment, he thought that the instrument's stabilization was faulty; then he realized, with a shock that jolted his entire concept of the universe, that Jupiter itself was moving, not the telescope. The evidence stared him in the face; he could also see two of the smaller moons – and they were quite motionless.
   He switched to a lower magnification, so that he could see the entire disk of the planet, now a leprous, mottled grey. After a few more minutes of incredulity, he saw what was really happening; but he could still scarcely believe it.
   Jupiter was not moving from its immemorial orbit, but it was doing something almost as impossible. It was shrinking – so swiftly that its edge was creeping across the field even as he focused upon it. At the same time the planet was brightening, from its dull grey to a pearly white. Surely, it was more brilliant than it had ever been in the long years that Man had observed it; the reflected light of the Sun could not possibly – At that moment, Sasha suddenly realized what was happening, though not why, and sounded the general alarm.
   When Floyd reached the observation lounge, less than thirty seconds later, his first impression was of the blinding glare pouring through the windows, painting ovals of light on the walls. They were so dazzling that he had to avert his eyes; not even the Sun could produce such brilliance.
   Floyd was so astonished that for a moment he did not associate the glare with Jupiter; the first thought that flashed through his mind was: Supernova! He dismissed that explanation almost as soon as it occurred to him; even the Sun's next-door neighbour, Alpha Centauri, could not have matched the awesome display in any conceivable explosion
   The light suddenly dimmed; Sasha had operated the external sun shields. Now it was possible to look directly at the source, and to see that it was a mere pinpoint – just another star, showing no dimensions at all. This could have nothing to do with Jupiter; when Floyd had looked at the planet only a few minutes ago, it had been four times larger than the distant, shrunken sun.
   It was well that Sasha had lowered the shields. A moment later, that tiny star exploded – so that even through the dark filters it was impossible to watch with the naked eye. But the final orgasm of light lasted only a brief fraction of a second; then Jupiter – or what had been Jupiter – was expanding once again.
   It continued to expand, until it was far larger than it had been before the transformation. Soon the sphere of light was fading rapidly, down to merely solar brilliance; and presently Floyd could see that it was actually a hollow shell, for the central star was still clearly visible at its heart.
   He did a quick mental calculation. The ship was more than one light-minute from Jupiter, yet that expanding shell – now turning into a bright-edged ring – already covered a quarter of the sky. That meant it was coming toward them at – My God! – nearly half the speed of light. Within minutes, it would engulf the ship.
   Until then, no one had spoken a word since Sasha's first announcement. Some dangers are so spectacular and so much beyond normal experience that the mind refuses to accept them as real, and watches the approach of doom without any sense of apprehension. The man who looks at the onrushing tidal wave, the descending avalanche, or the spinning funnel of the tornado, yet makes no attempt to flee, is not necessarily paralysed with fright or resigned to an unavoidable fate. He may simply be unable to believe that the message of his eyes concerns him personally. It is all happening to somebody else.
   As might have been expected, Tanya was the first to break the spell, with a series of orders that brought Vasili and Floyd hurrying to the bridge.
   'What do we do now?' she asked, when they had assembled.
   We certainly can't run away, thought Floyd. But perhaps we can improve the odds.
   'The'ship's broadside on,' he said. 'Shouldn't we turn away from that thing so we're a smaller target? And get as much of our mass as we can between it and us, to act as a radiation shield?'
   Vasili's fingers were already flying over the controls.
   'You're right, Woody – though it's already too late as far as any gammas and X rays are concerned. But there may be slower neutrons and alphas and heaven knows what else still on the way.'
   The patterns of light began to slide down the walls as the ship turned ponderously on its axis. Presently they vanished completely; Leonov was now oriented so that virtually all its mass lay between the fragile human cargo and the approaching shell of radiation.
   Will we actually feel the shock wave, wondered Floyd, or will the expanding gases be too tenuous to have any physical effect by the time they reach us? Seen from the external cameras, the ring of fire now almost encircled the sky. But it was fading rapidly; some of the brighter stars could even be seen shining through it. We're going to live, thought Floyd. We've witnessed the destruction of the greatest of planets – and we've survived.
   And presently the cameras showed nothing except stars – even if one was a million times brighter than all the others. The bubble of fire blown by Jupiter had swept harmlessly past them, impressive though it had been. At their distance from the source, only the ship's instruments had recorded its passing.
   Slowly, the tension aboard relaxed. As always happens in such circumstances, people started to laugh and to make silly jokes. Floyd scarcely heard them; despite his relief at still being alive, he felt a sense of sadness.
   Something great and wonderful had been destroyed. Jupiter, with all its beauty and grandeur and now never-to-be-solved mysteries, had ceased to exist. The father of all the gods had been struck down in his prime.
   Yet there was another way of looking at the situation. They had lost Jupiter: What had they gained in its place?
   Tanya, judging her moment nicely, rapped for attention.
   'Vasili – any damage?'
   'Nothing serious – one camera burned out. All radiation meters still well above normal, but none near danger limits.'
   'Katerina – check the total dosage we've received. It looks as if we were lucky, unless there are more surprises. We certainly owe a vote of thanks to Bowman – and to you, Heywood. Do you have any idea what happened?'
   'Only that Jupiter's turned into a sun.'
   'I always thought it was much too small for that. Didn't someone once call Jupiter "the sun that failed"?'
   'That's true,' said Vasili, 'Jupiter is too small for fusion to start – unaided.'
   'You mean, we've just seen an example of astronomical engineering?'
   'Undoubtedly. Now we know what Zagadka was up to.'
   'How did it do the trick? If you were given the contract, Vasili, how would you ignite Jupiter?'
   Vasili thought for a minute, then shrugged wryly. 'I'm only a theoretical astronomer – I don't have much experience in this line of business. But let's see... Well, if I'm not allowed to add about ten Jupiter masses, or change the gravitational constant, I suppose I'll have to make the planet denser – hmm, that's an idea...'
   His voice trailed off into silence; everyone waited patiently, eyes flickering from time to time to the viewing screens.
   The star that had been Jupiter seemed to have settled down after its explosive birth; it was now a dazzling point of light, almost equal to the real Sun in apparent brilliance.
   'I'm just thinking out loud – but it might be done this way. Jupiter is – was – mostly hydrogen. If a large percentage could be converted into much denser material – who knows, even neutron matter? – that would drop down to the core. Maybe that's what the billions of Zagadkas were doing with all the gas they were sucking in. Nucleosynthesis – building up higher elements from pure hydrogen. That would be a trick worth knowing! No more shortage of any metal – gold as cheap as aluminium!'
   'But how would that explain what happened?' asked Tanya.
   'When the core became dense enough, Jupiter would collapse – probably in a matter of seconds. The temperature would rise high enough to start fusion. Oh, I can see a dozen objections – how would they get past the iron minimum; what about radiative transfer; Chandrasekhar's limit. Never mind. This theory will do to start with; I'll work out the details later. Or I'll think of a better one.'
   'I'm sure you will, Vasili,' Floyd agreed. 'But there's a more important question. Why did they do it?'
   'A warning?' ventured Katerina over the ship's intercom.
   'Against what?'
   'We'll find that out later.'
   'I don't suppose,' said Zenia diffidently, 'that it was an accident?'
   That brought the discussion to a dead halt for several seconds.
   'What a terrifying idea!' said Floyd. 'But I think we can rule it out. If that was the case, there'd have been no warn – Perhaps. If you start a forest fire because you've been careless, at least you do your best to warn everyone.'
   'And there's another thing we'll probably never know,' lamented Vasili. 'I always hoped Carl Sagan would be right, and there'd be life on Jupiter.'
   'Our probes never saw any.'
   'What chance did they have? Would you find any life on Earth, if you looked at a few hectares of the Sahara or the Antarctic? That's about all we ever did on Jupiter.'
   'Hey!' said Brailovsky. 'What about Discovery – and Hal?' Sasha switched on the long-range receiver and started to search on the beacon frequency. There was no trace of a signal.
   After a while, he announced to the silently waiting group:
   'Discovery's gone.'
   No one looked at Dr Chandra; but there were a few muted words of sympathy, as if in consolation to a father who had just lost a son.
   But Hal had one last surprise for them.

53 – A Gift of Worlds

   The radio message beamed to Earth must have left Discovery only minutes before the blast of radiation engulfed the ship. It was in plain text and merely repeated over and over again:
   ALL THESE WORLDS ARE YOURS – EXCEPT EUROPA.
   ATTEMPT NO LANDINGS THERE.
   There were about a hundred repetitions; then the letters became garbled, and the transmission ceased.
   'I begin to understand,' said Floyd, when the message had been relayed by an awed and anxious Mission Control.
   'That's quite a parting present – a new sun, and the planets around it.'
   'But why only three?' asked Tanya.
   'Let's not be greedy,' Floyd replied. 'I can think of one very good reason. We know there's life on Europa. Bowman – or his friends, whoever they may be – want us to leave it alone.'
   'That makes good sense in another way,' said Vasili. 'I've been doing some calculations. Assuming that Sol 2 has settled down and will continue to radiate at its present level, Europa should have a nice tropical climate – when the ice has melted. Which it's doing pretty quickly right now.'
   'What about the other moons?'
   'Ganymede will be quite pleasant – the dayside will be temperate. Callisto will be very cold; though if there's much outgassing, the new atmosphere may make it habitable. But Io will be even worse than it is now, I expect.'
   'No great loss. It was hell even before this happened.'
   'Don't write off Io,' said Curnow. 'I know a lot of Texarab oilmen who'd love to tackle it, just on general principles. There must be something valuable, in a place as nasty as that. And by the way, I've just had a rather disturbing thought.'
   'Anything that disturbs you must be serious,' said Vasili. 'What is it?'
   'Why did Hal send that message to Earth, and not to us? We were much closer.'
   There was a rather long silence; then Floyd said thoughtfully: 'I see what you mean. Perhaps he wanted to make certain it was received on Earth.'
   'But he knew we would relay it – oh!' Tanya's eyes widened, as if she had just become aware of something unpleasant.
   'You've lost me,' complained Vasili.
   'I think this is what Walter's driving at,' said Floyd. 'It's all very well to feel grateful to Bowman – or whatever gave that warning. But that's all they did. We could still have been killed.'
   'But we weren't,' answered Tanya. 'We saved ourselves – by our own efforts. And perhaps that was the whole idea. If we hadn't – we wouldn't have been worth saving. You know, survival of the fittest. Darwinian selection. Eliminating the genes for stupidity.'
   'I've an unpleasant feeling you're right,' said Curnow. 'And if we'd stuck to our launch date, and not used Discovery as a booster, would it, or they, have done anything to save us? That wouldn't have required much extra effort for an intelligence that could blow up Jupiter.'
   There was an uneasy silence, broken at last by Heywood Floyd.
   'On the whole,' he said, 'I'm very glad that's one question we'll never get answered.'

54 – Between Suns

   The Russians, thought Floyd, are going to miss Walter's songs and wisecracks on the way home. After the excitement of the last few days, the long fall Sunward – and Earthward – will seem a monotonous anticlimax. But a monotonous, uneventful trip was what everyone devoutly hoped for.
   He was already feeling sleepy, but was still aware of his surroundings and capable of reacting to them. Will I look as dead when I'm in hibernation? he asked himself. It was always disconcerting to look at another person – especially someone very familiar – when he had entered the long sleep.
   Perhaps it was too poignant a reminder of one's own mortality.
   Curnow was completely out, but Chandra was still awake, though already groggy from the final injection. He was obviously no longer himself, for he seemed quite unperturbed by his own nakedness or Katerina's watchful presence. The gold lingam that was his only article of clothing kept trying to float away from him, until its chain recaptured it.
   'Everything going okay, Katerina?' asked Floyd.
   'Perfectly. But how I envy you. In twenty minutes, you'll be home.'
   'If that's any consolation – how can you be sure we won't have some horrible dreams?'
   'No one's ever reported any.'
   'Ah – they may forget them when they wake up.'
   Katerina, as usual, took him quite seriously. 'Impossible. If there were dreams in hibernation, the EEG records would have revealed them. Okay, Chandra – close your eyes. Ah – there he goes. Now it's your turn, Heywood. The ship will seem very strange without you.'
   'Thanks, Katerina... hope you have a nice trip.'
   Drowsy though he was, Floyd became aware that Surgeon-Commander Rudenko seemed a little uncertain, even – could it be? – shy. It looked as if she wanted to tell him something, but couldn't make up her mind.
   'What is it, Katerina?' he said sleepily.
   'I haven't told anyone else yet – but you certainly won't be talking. Here's a little surprise.'
   'You'd... better... hurry...'
   'Max and Zenia are going to get married.'
   'That... is... supposed... to... be... a... surprise?...'
   'No. It's just to prepare you. When we get back to Earth, so are Walter and I. What do you think of that?'
   Now I understand why you were spending so much time together. Yes, it is indeed a surprise... who would have thought it!
   'I'm... very... happy... to... hear...'
   Floyd's voice faded out before he could complete the sentence. But he was not yet unconscious, and was still able to focus some of his dissolving intellect on this new situation.
   I really don't believe it, he said to himself. Walter will probably change his mind before he wakes up.
   And then he had one final thought, just before he went to sleep himself. If Walter does change his mind, he'd better not wake up.
   Dr Heywood Floyd thought that was very funny. The rest of the crew often wondered why he was smiling all the way back to Earth.