Arthur C. Clarke

2010: ODYSSEY TWO
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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.'