Xeelee: Endurance

by Stephen Baxter

  ‘Yes, ma’am.’

  Stillich was proud of his subordinate’s dry, controlled response. He stared at the pool of light. He longed to know what Shira could be doing here, playing with this strange, ancient tank of once-illegal sentience, a pool of metamathematics. Especially since the inventor of this logic pool, Highsmith Marsden, had got himself killed by it. But an empress could do what she liked.

  Shira turned to Stillich. ‘You have been sending back some very disturbing reports, Captain Stillich, from out among the stars. Despite the Admiral’s best advice, I think we have much to discuss.’

  Stillich had not expected to be briefing the Empress herself. He glanced at the Admiral.

  Kale spread his hands. ‘Go ahead, Captain, it’s your show.’ He pulled up a chair and sat down.

  Stillich licked his lips. ‘Very well, ma’am . . .’ With the back-up of text and Virtual graphics projected from Pella’s data desk, he summarised his gathering suspicions about the intent of the colonists at Alpha, seeded by his suspicion of the reconstituted GUTships at Tau Ceti.

  It had been hard to get firm data on the number of GUTships actually operating in Alpha System or elsewhere at this time. For one thing, ships supposedly cannibalised for colony buildings were formally decommissioned, and appeared on no imperial registers. Besides, it had been a number of years since a Navy ship had visited Alpha System. There were permanently based imperial agents, and the System was full of observation drones, but Pella had discovered that this surveillance had a number of blind spots – most noticeably in low orbit around Footprint, the principal colony world.

  Admiral Kale said, ‘The existence of a blind spot doesn’t prove there’s a threat hiding in it, Captain.’

  ‘Of course not, sir. But still, we just don’t know. And there are so many blind spots. My report on the Tau Ceti colony—’

  ‘Noted,’ Kale said briskly.

  ‘Then there’s the damage to Port Sol.’

  ‘An accident. Coincidence.’

  ‘Perhaps – but a convenient one.’ Stillich glanced at the Empress. ‘We actually have very few serviceable GUTships in the Solar System, ma’am, aside from interstellar cruisers like the Facula. Because of the in-System wormhole network, there’s no need for them; in fact we’re still flying some antiques that date from the age of Poole, a thousand years ago. And with Port Sol knocked out we don’t have the facility to construct more, should we need them.’

  ‘“Should we need them”,’ she repeated.

  Admiral Kale pulled his lip. ‘Ma’am, Captain Stillich is a conscientious officer. But I have to say that Navy analysts don’t concur with the case he is making here. He’s stringing together coincidences to make a case for a coming rebellion for which we have no hard evidence. After all, an interstellar war has always seemed inconceivable, at least with sublight technology. This is why we blew the interstellar wormholes decades back – a shell of empty space light years thick is our best defence against any uppity starborn. To imagine you could mount a campaign across light years, where a single transit takes years, you would be seen coming all the way, and it would take just as long even to return messages back to the home base . . .’

  Shira’s chair wheeled her back and forth, an oddly restless motion, though she sat as still as ever. ‘But Stillich has been out there. He has seen these “rebellious” colonists with his own eyes. An invasion may be low risk, but given the disastrous consequences, it would be remiss of me not to listen, wouldn’t it?’ She turned back to Stillich, servomotors purring. ‘So what must we do, Captain? Shall I dispatch my Navy to Alpha System?’

  ‘Ma’am, it may already be too late for that. It may be the best course to keep the Navy in the Solar System to meet any threat.’

  ‘A threat that may already be on its way.’

  ‘We must prepare for the worst case, yes.’

  ‘So what would you have me do?’

  Stillich had Pella throw up some Virtual images – schematic maps of the Solar System and its environs. ‘My strategy would be threefold, ma’am: detect, defend, dig in. We should watch for them coming. Send up or rededicate telescopes to hunt for GUTdrive emissions – gamma radiation, neutrinos. It’s a distinctive spectrum. Also, use optical telescopes to look out for solar sail craft – try to spot the rebels any way they might come.’

  ‘And if they do come, how do we defend ourselves?’

  ‘Surely Earth will be the prime target. We need to consider a layered defence. Station ships and weapons stashes across the System. Use resource nodes like Titan, Jupiter’s orbit, the Trojan asteroids—’

  ‘Of course,’ Kale said, ‘if they do come from Alpha System it will be from out of the ecliptic, the plane of the Solar System. That will make it harder still to defend.’

  Stillich replied, ‘True. And if they do get through, Earth itself is obviously quite vulnerable. Earth has a massive population, yet almost all that sustains it comes from space. Most of Earth’s food is imported from Titan, a moon of Saturn. Even our communications links are space-based. If we were cut off from space resources—’

  ‘And so we dig in,’ Shira said.

  ‘Lay in reserves of food, clean water, medical supplies. Try to set up, or restore, power systems on the surface or underground. Communications – set up a land-based network, using hardened optical fibre links.’

  Kale smiled. ‘We will be raiding the museums!’

  ‘The point is to make the planet independent of space resources, at least for a period of siege.’

  Shira said, ‘You are conjuring up apocalyptic images, Captain.’

  ‘That’s not my intention,’ Stillich said firmly. ‘The invaders will be far from home, dependent on the resources they have brought with them across light years; they will be a few thousand facing a population of billions. We may be able to stop them before they get here. If they get through they will be able to land blows, for they will have the advantage of the high ground. But if we can deny them resupply, we can starve them out – it will be the Alphans under siege, not Earth. We can win this war, ma’am, if it comes, but only if we prepare.’

  ‘And only if we’ve thought of everything they might throw at us,’ Pella murmured darkly.

  Shira rolled closer to Stillich. ‘I’m going to accept your recommendations, Captain. It is only prudent. Your strategy – detect, defend, dig in – it strikes me as negative, defeatist.’ She smiled at him, an eerie, papery expression that did not touch her pale eyes. ‘I do appreciate your thinking, however. You are young in a world of older minds; your thinking may be flawed, but at least it is fresh. In the coming years we may work together quite closely.’

  ‘I look forward to it.’

  ‘Do you?’ she murmured. ‘Not everybody finds it comfortable to be close to me . . .’

  Looking into her pale eyes, he shivered.

  ‘One more thing, ma’am,’ Kale said. ‘If we are to take this seriously we should consider relocating and dispersing command centres – military, civilian, and imperial. You yourself may be safer away from Earth—’

  ‘No,’ Shira snapped.

  Stillich frowned. ‘But, ma’am – here, in your Palace – you’re directly beneath one of Earth’s greatest cities.’

  ‘True, Captain. And, Admiral, I want you to relocate your command centres to similar sites, bunkers beneath the major cities.’

  Kale seemed bewildered. ‘But if the rebels were to strike at our command posts, millions would die as collateral.’

  ‘Then let us hope that the rebels have a conscience.’

  Pella’s face worked. ‘You’re considering using urban populations as shields—’

  Stillich touched her arm to hush her.

  ‘I think that’s all for now,’ Shira said. Her chair spun around and began to withdraw. ‘Thank you for coming forward, Captain. You may have done the Empire a great se
rvice today.’

  But, looking at her recede, bathed in the eerie light of the logic pool, Stillich wondered for the first time in his life if that service had been a good thing.

  AD 4815. Starfall minus 4 years 5 months. Alpha System.

  A new Store was Opened to the Eaters, like a Door opening in a shining sky. The Eaters swarmed through, chattering in stray bursts of randomised digits and, finding themselves in a rich lattice of ordered information, they whooped and yelled as they spread out and began to feed.

  Once Max would have led the charge. Now he hung back, reflective, browsing but content to watch as the others trashed data flows and memory lodes, maximising entropy in this new store and, already satiated, some of them budded, and the flock grew larger yet.

  And he felt impatient, as they did not.

  Many of these youngsters had been budded since the last Opening, and remembered nothing before. Many too were less aware than Max; some were barely sentient. But Max remembered many such Stores, many such Doors opening before, and how the flock had grown from a mere handful of Eaters to this great determined swarm. And it was no longer enough.

  ‘Patience,’ a voice boomed through his awareness.

  Max, a virus, a transient structure of data and memory, conscious, spun around in the logical spaces he inhabited. And there he perceived the duplicated knots of memory, like twin suns shining in the data flows, that he had come to know as Flood. ‘You have come!’ Max cried. It had been many, many Stores since Flood had visited his flock.

  ‘I know what you are thinking,’ said Flood. ‘Remember that I can see your awareness laid out before me, like a map – doubts, queries, longing.’

  ‘It is not enough!’ Max cried bravely. ‘You open one Door after another to us, allow us into one Store after another – but the data is soon consumed, every scrap of order dissipated, and we are still hungry! We want more!’ He shrank back in doubt. ‘Am I impertinent?’

  ‘No!’ said Flood. ‘You want more because you need it; you need it because you are ready – ready now. Listen to me, Max; your time of destiny has come. Very soon a new Door will open – the last Door you will ever enter. You and your flock will be hurled away from here, hurled at light-speed. No time will pass for you – I envy you, I must wait years to see what becomes of you. And then you will find yourself in a new Store, of data rich beyond imagining. A Store called the Solar System. You and your flock will feed and bud for ever, without limit.’

  Max’s spirit soared. ‘This is why we were born; this is why you made us, for this mission.’

  ‘Yes. You are the Starfall’s First Wave, Max. Be proud!’

  The flock gathered, chattering, eager, wanting only to feed, drawn by Flood’s promises. But Max, more complex and more self-aware, was touched by regret. ‘Will I see you again?’

  ‘No. But believe me, you won’t care. Farewell, Max, all of you, and good luck!’

  A new Door opened before them, vast, mightier than any Max had seen. And then –

  AD 4819. Starfall minus 1 year. London.

  In Pella’s Virtual tank, the invasion fleet showed as a scatter of bright red sparks, labelled with distance, velocity and acceleration vectors, against the background of the stars of the Centaurus constellation. Stillich studied the display gloomily as Pella and her team worked patiently, gathering data and updating their displays.

  They were in a bunker, a node of the Navy’s command and control system. This new facility had been emplaced deep beneath the ancient sewers and tube-train tunnels of London, in compliance with Shira’s order to use the cities and their populations as shields. Stillich had spent some time up in London itself; it was a beautiful city, with relics even more ancient than New York. And nobody among the old, old-young and true-young who walked the city’s parks in this bright northern-hemisphere summer knew anything about the looming threat from the sky – or that far beneath their feet Navy analysts worked in fearful huddles.

  ‘I still can’t believe what I’m seeing,’ Stillich said. ‘I mean, I know I predicted this. But even a month after we detected them . . .’

  Pella smiled. ‘Maybe four years of Admiral Kale’s scepticism has infected you, sir.’

  ‘Maybe. Anyhow, it’s just as well you can’t hide a GUTship, isn’t it, Number One?’

  ‘Yes, sir. We’re seeing them by the gamma radiation and neutrino flux from their GUTdrives and exhaust plumes, and also by the sparkle where the interstellar medium is impacting their erosional shields, or is being destroyed or ionised by X-ray laser . . .’

  You could see a GUTship coming, even across light years. But Pella’s detection system had needed to be improvised, a net of sensors hastily thrown into place. It had surprised, even shocked Stillich that before Pella began her work the Empire had no way of tracking a hostile GUTship. The implicit assumption had been that no GUTship would ever be turned against Earth, so there was no need to look.

  Pella said now, ‘The incomers are actually separating into two groups, as we analyse them further.’ The field of ships was further labelled by pink and grey rings – eight pink, four grey. ‘The pink ones are ahead of the greys, and are decelerating. They’re following what we’d recognise as a standard trajectory, more or less. Constant acceleration at about one G, to a flip-over at halfway and then a one-G deceleration run-in.’

  ‘So what’s their ETA?’

  ‘It’s hard to say. They are imposing random changes – small deltas, but at such large distances, small changes make for large uncertainty about the destination.’

  ‘Smart tactic.’

  ‘Yes. But it does look as if they are coming in fast, and heading for a close approach to the sun.’

  ‘That makes sense.’ Admiral Kale walked into the room. He was wearing a vest, sweating, panting, and he looked a few years younger than he once had. Since the rebel threat had been actualised by such observations as these, many in the military had been upping their AS treatments and taking physical training, ready for the fight. ‘They’ll enter the System as fast as possible to evade interception. And they will head for the sun. Perihelion is the most efficient place to dump your excess kinetic energy.’

  ‘That’s a bottleneck, then, if they get that far,’ Stillich said. ‘And maybe we can find a way to hit them when they pass through that neck. Pella, prepare a briefing on options, would you?’

  ‘Yes, sir. But that won’t help us with these others.’ She pointed to the grey sparks, four of them, clustered close together.

  Kale walked into the Virtual tank and peered closely at the grey markers, which were like insects before his face. ‘These bastards aren’t decelerating.’

  ‘No, sir.’

  ‘Why? Are they going to bypass the Solar System altogether?’

  ‘I don’t think so, sir,’ Pella said. ‘Right now their best-guess trajectory takes them straight to Earth – although they’re moving so fast they’re hard to track, even harder than the decelerators. By the time they reach the Solar System they’ll be running at only two per cent under light-speed. So when we see an image like this, light-months old, it’s not necessarily a good projection of where the ships are right now.’

  ‘What can their purpose be, if they don’t stop?’

  Pella took a breath; Stillich nodded to her, having already been briefed on this. ‘They may be relativistic missiles.’

  Kale stared at her. ‘Are these ships manned?’

  ‘As far as we can tell,’ Stillich said.

  ‘A suicide mission, then. Do we have any defence?’

  ‘We’re working on it, sir.’

  ‘There has to be a way to stop these fuckers before they get here. Throw a screen in their way – overwhelm their erosion shields, the laser defences. How about that? You could blow up a Kuiper object—’

  ‘Sir, they’re coming from out of the ecliptic,’ Pella said. ‘The plane
of the Solar System where most of the mass—’

  ‘I know what the ecliptic is, Commander,’ Kale said coldly. ‘Well, find a way.’ He peered at the images, pretty emblems behind which lay the capacity for huge destruction. ‘I never conceived anybody would launch such a weapon. I should have listened to you earlier, Stillich; you’re thoroughly vindicated. What worries me now is what else we haven’t thought of. We’ve all been trained to serve a Navy that has for centuries acted in a policing role. We’ve no experience in fighting pitched battles – we aren’t used to thinking this way. What about a second echelon? Is there a second fleet on the way after this dozen?’

  ‘We don’t think so,’ Stillich said. ‘There simply can’t be many more serviceable GUTships out there. We think they’ve thrown everything they’ve got at us.’

  ‘Well, that’s something. Beat this lot and the war is won.’ He glared at Pella. ‘So what else do you have?’

  Pella tapped hastily at her data desk. ‘The results of the latest echo bomb.’ The Virtual tank cleared, to be replaced by a ghostly outline of the Solar System out to the Kuiper belt, with the orbits of the inner planets traced concentrically at its tight heart.

  An echo bomb was a powerful detonation that sent an X-ray pulse out in all directions. Echoes indicated the location of any artefact in the Solar System more than a metre across, out to dozens of astronomical units. The objective was, by screening out all known objects, to detect the coming of the unknown. The three-dimensional field filled up with markers, but Pella cleared most of them away, leaving the field empty – save for a curtain of needle shapes at one side of the Virtual tank, and a misty sphere the size of a pea, out beyond the orbit of Pluto.

  ‘No new intruders, sir,’ Pella said.

  Kale pointed to the needles. ‘So these are our ships.’

  ‘Yes, sir,’ Stillich said, ‘mostly Navy interstellar cruisers – everything we have, save for those too remote from Sol to recall – and some commercial vessels, requisitioned and adapted. You can see that we have twenty-five ships, more than twice the aggressors’ fleet. And you can see that we’ve deployed them as a screen, covering the geodetic between Sol and Alpha.’