Phase Space

by Stephen Baxter

  Everywhere, that is, except for one corner of the sky blocked by a vaguely elliptical shadow, sharp-edged, one rim picked out by the sun.

  It was Ra-Shalom: Greenberg’s destination.

  He was looking along the length of the Ehricke’s hab module. It was a tight cylinder, just ten metres long and seven wide, home to four crew for this year-long jaunt. The outer hull was crammed with equipment, sensors and antennae clustered over powder-white and gold insulating blankets. At the back of the hab module he could see the bulging upper domes of the big cryogenic fuel tanks, and when he turned the other way there was the Earth-return module, an Apollo-sized capsule stuck sideways under the canopy of the big aerobrake.

  The whole thing was just a collection of cylinders and boxes and canopies, thrown together as if at random, a ropy piece of shit.

  But in a vessel such as this, Americans planned to sail to Mars.

  Not Oliver Greenberg, though.

  One small step time, he thought.

  He pulled himself tentatively along the slide wire and made his way to the PMU station, on the starboard side of the hab module. The Personal Manoeuvring Unit was a big backpack shaped like the back and arms of an armchair, with foldout head- and leg-rests on a tubular frame. Greenberg ran a quick check of the PMU’s systems. It was old Shuttle technology, cannibalized from the Manned Manoeuvring Units that had enabled crew to shoot around orbiter cargo bays. But today, it was being put to a use its designers never dreamed of.

  He turned around, and backed into the PMU.

  ‘Ehricke, EV1,’ he said. ‘Suit latches closed.’

  ‘Copy that.’

  He pulled the PMU’s arms out around him and closed his gloved hands around the hand-controllers on the end of the arms. He unlatched the folded-up body frame. He rested his neck against the big padded rest, and settled his feet against the narrow footpads at the bottom of the frame, so he was braced. Today’s EVA was just a test reconnaissance, but a full field expedition to Ra could last all of eight hours; the frame would help him keep his muscle movements down, and so reduce resource wastage.

  Greenberg released his tethers. A little spring-loaded gadget gave him a shove in the back, gentle as a mother’s encouraging pat, and he floated away from the bulkhead.

  … Suddenly he didn’t have hold of anything, and he was falling.

  Oh, shit, he thought.

  He had become an independent spacecraft. The spidery frame of the PMU occulted the dusting of stars around him.

  He tested out his propulsion systems.

  He grasped his right-hand controller, and pushed it left. There was a soft tone in his helmet as the thruster worked; he saw a faint sparkle of exhaust crystals, to his right. In response to the thrust, he tipped a little to the left. He had four big fuel tanks on his back, and twenty-four small reaction control-system nozzles. In fact he had two systems, a heavy-duty hot gas bipropellant system – kerosene and nitric acid – for the big orbital changes he would have to make to reach Ra, and a cold-gas nitrogen thruster for close control at the surface of the rock.

  When he started moving, he just kept on going, until he stopped himself with another blip of his thrusters.

  Greenberg tipped himself up so he was facing Ra-Shalom, with the Ehricke behind him.

  ‘Ehricke, I’m preparing to head for Ra.’

  ‘We copy, Oliver.’

  He fired his kerosene thruster and felt a small, firm shove in the small of his back. Computer graphics started to scroll across the inside of his face plate, updating burn parameters. He was actually changing orbit here, and he would have to go through a full rendezvous procedure to reach Ra. That was what had gotten him this job, in fact. Greenberg had flown several of the missions which docked a Shuttle orbiter with the old Mir, and then with the Space Station. He had even been chief astronaut, for a while.

  Then the VentureStar had outdated his piloting skills, and he was grounded, at age fifty.

  NASA was full of younger guys now, preparing for the LMP, the Lunar-Mars Programme that was at the heart of NASA’s current strategy, inspired by the evidence the sample-return probes had come up with of life on Mars.

  This mission, a year-long jaunt to the near-Earth asteroid Ra-Shalom, was a shakedown test of the technologies that would be needed to get to Mars. Ra provided an intermediate goal, between lunar flights of a few weeks and the full Mars venture that would take years, setting major challenges in terms of life-support loop closure and systems reliability.

  But there was also, he was told, good science to be done here.

  Not that he gave a shit about that.

  He was only here, tinkering with plumbing and goddamn pea plants, because nobody else in the Office had wanted to be distracted from the competition for places on the Mars flights to come.

  The angle of the sun was changing, and the slanting light changed Ra from a flat silhouette to a potato-shaped rock in space, fat and solid. Ra’s surface was crumpled, split by ravines, punctured by craters of all sizes. There was one big baby that must have been a kilometre across, its walls spreading around the cramped horizon.

  The rock was more than three kilometres long, spinning on its axis once every twenty hours. It was as black as coal dust. Ra-Shalom was a C-type asteroid – carbonaceous, fat with light elements, coated by carbon deposits. It had probably formed at the chilly outer rim of the asteroid belt. Ra was like a folded-over chunk of the Moon, its beat-up surface a record of this little body’s dismal, violent history.

  At a computer prompt, he prepared for his final burn. ‘Ready for Terminal Initiation.’

  ‘Copy that, Oliver.’

  One last time the kerosene thrusters fired, fat and full.

  ‘Okay, EV1, Ehricke. Coming up to your hundred-metre limit.’

  ‘Copy that.’

  He came to a dead stop, a hundred metres from the surface of Ra-Shalom. The asteroid’s complex, battered surface was like a wall in front of him. He felt no tug of gravity – Ra’s G was less than a thousandth of Earth’s – it would take him more than two minutes to fall in to the surface from here, compared to a few seconds on Earth.

  He was comfortable. The suit was quiet, warm, safe. He could hear the whir of his backpack’s twenty-thousand rpm fan. But he missed the squeaks and pops on the radio which he got used to in LEO as he drifted over UHF stations on the ground.

  He blipped his cold-gas thrusters, and drifted forward. This wasn’t like coming in for a landing; it was more like walking towards a cliff face, which bulged gently out at him, its coal-like blackness oppressive. He made out more detail, craters overlaid on craters down to the limit of visibility.

  He tweaked his trajectory once more, until he was heading for the centre of a big crater, away from any sharp-edged crater walls or boulder fields. Then he just let himself drift in, at a metre a second. If he used the thrusters any more he risked raising dust clouds that wouldn’t settle. There were four little landing legs at the corners of his frame; they popped out now, little spear-shaped penetrators designed to dig into the surface and hold him there.

  The close horizon receded, and the cliff face turned into a wall that cut off half the universe.

  He collided softly with Ra-Shalom.

  The landing legs, throwing up dust, dug into the regolith with a grind that carried through the PMU structure. The dust hung about him. Greenberg was stuck here, clinging to the wall inside his PMU frame like a mountaineer to a rock face.

  He turned on his helmet lamp. Impact glass glimmered.

  Unexpectedly, wonder pricked him. Here was the primordial skin of Ra-Shalom, as old as the solar system, just centimetres before his face. He reached out and pushed his gloved hand into the surface, a monkey paw probing.

  The surface was thick with regolith: a fine rock flour, littered with glassy agglutinates, asteroid rock shattered by aeons of bombardment. His fingers went in easily enough for a few centimetres – he could feel the stuff crunching under his pressure, as if he was diggin
g into compacted snow – but then he came up against much more densely packed material, tamped down by the endless impacts.

  He closed his fist and pulled out his hand. A cloud of dust came with it, gushing into his face like a hail of meteorites. He looked at the material he’d dug out. There were a few bigger grains here, he saw: it was breccia, bits of rock smashed up in multiple impacts, welded back together by impact glass. There was no gravity to speak of; the smallest movement sent the fragments drifting out of his palm.

  His glove, pristine white a moment ago, was already caked black with dust. He knew the blackness came from carbon-rich compounds. There were hydrates too: water, locked up in the rock, just drifting around out here. In fact rocks like Ra were the only significant water deposits between Earth and Mars. It might prove possible to use the rock’s resources to close the loops of mass and energy circulating in Ehricke’s life support, even on this preliminary jaunt.

  Ra could probably even support some kind of colony, off in the future. So it was said.

  Greenberg had always preferred to leave the sci-fi stuff to the wackos in the fringe study groups in NASA, and focus on his checklist. Still, it was a nice thought.

  He allowed himself a moment to savour this triumph. Maybe he would never get to Mars. But he was, after all, the first human to touch the surface of another world since Apollo 17.

  He pushed his hand back into the pit he’d dug, ignoring the fresh dust he raised.

  The cloud was scattered, thin and dark, across ten light years. It was gas laced with dust grains – three-quarters hydrogen, the rest helium, some trace elements – visible only to any observers as a shadow against the stars.

  When the supernova’s gale of heavy particles washed over it, the cloud’s stability was lost. It began to fall in on itself.

  In a ghostly inverse of the inciting supernova explosion, the core of the cloud heated up as material rained in upon it, its rotation speeding up, an increasingly powerful electromagnetic field whipping through the outer debris. The core began to glow, first at infra-red wavelengths, and then in visible light.

  It was the first sunlight.

  Scale: Exp 2

  Oliver Greenberg was bored.

  He was actually glad to get the call from Gita Weissman about the balky rock splitter in Shaft Seven, even though the lost time would mean they weren’t going to make quota this month.

  At least it made a change from the usual CELSS problems, CELSS for closed environment and life-support systems, a term nobody used except him any more. Even after a century, nobody had persuaded a pea plant to grow nice straight roots in microgravity, and the loss from the mass loops in the hydroponic tanks continued at a stubborn couple of per cent a month, despite the new generation of supercritical water oxidizers they used to reduce their solid wastes.

  It’s still about pea plants and plumbing, he thought dismally.

  He started clambering into his skinsuit, hauling the heavy fabric over his useless legs.

  He took a last glance around the glass-wall displays of his hab module. It shocked him when the displays showed him he was the only one of Ra’s two thousand inhabitants on the surface.

  Well, hell, it suited him out here, even if it had stranded him in this lonely assignment, monitoring the systems that watched near-Ra space. Most of the inhabitants of Ra had been born up here, and lived their lives encased in the fused-regolith walls of old mine shafts. They didn’t know any better.

  Greenberg, though, preferred to keep a weather eye on the stars, unchanged since his Iowa boyhood. He even liked seeing Earth swim past on its infrequent close approaches, like a blue liner on a black ocean, approaching and receding. It made him nostalgic. Even if he couldn’t go home any more.

  Suited up, he shut down the glass-wall displays. The drab green walls of the hab module were revealed, with their equipment racks and antique bathroom and galley equipment and clumsy-looking up-down visual cues. This was just an old Space Station module, dragged out here and stuck to the surface of Ra-Shalom, covered over with a couple of metres of regolith. He was tethered in the rim shadow of Helin Crater, the place he’d landed on that first jaunt in the Ehricke. And that had been all of a hundred years ago, my God.

  He pushed his way through the diaphragm lock set in the floor of his hab module. He was at the top of one of Shaft Two, one of the earliest they’d dug out, with those first clumsy drill-blast-muck miners. It was a rough cylinder ten metres across, lined with regolith glass and hung with lamps and tethers; it descended beneath him, branching and curving.

  He grabbed hold of a wall spider, told it his destination, and let it haul him on down into the tunnel along its stay wires.

  Thus, clinging to his metal companion, he descended into the heart of Ra-Shalom.

  His legs dangled uselessly, and so he set his suit to tuck them up to his chest. He was thinking of taking the surgeons’ advice, and opting for amputation. What the hell. He was a hundred and fifty years old, give or take; he wasn’t going to start complaining.

  Anyhow, apart from that, the surgeons were preserving him pretty well. They were treating him to a whole cocktail of growth hormones and DHEA and melatonin treatments and beta-carotene supplements, not to mention telomere therapy and the glop those little nano-machines had painted on the surface of his shrivelled-up brain to keep him sharp.

  These guys were good at keeping you alive.

  This asteroid was small. A stable population was important, and a heavy investment in training needed a long payback period to be effective. So the birth rate was low, and a lot of research was directed to human longevity.

  He understood the logic. But still, he missed the sound of children playing, every now and again. The youngsters here didn’t seem to mind that, which made them a little less than human, in his view. But maybe that was part of the adjustment humans were having to make, as they learned to live off-Earth.

  In fact he missed his own kids, his daughters, even though, astonishingly, they were now both old ladies themselves.

  The surgeons had even managed to repair some of the cumulative microgravity damage he’d suffered over the years. For instance, his skeletal and cardiac muscles were deeply atrophied. Until they found a way to stabilize it, his bone calcium had continued to wash out in his urine, at a half per cent a month. At last, the surgeons said, the inner spongy bone, the trabeculae, had vanished altogether, without hope of regeneration.

  He never had been too conscientious about his time in the treadmills. It had left him a cripple, on Earth.

  So, at age eighty, he’d left Earth.

  Even then they had been closing down the cans – the early stations starting with Mir and the Space Station, that had relied completely on materials brought up from Earth. In retrospect it just didn’t make sense to haul material up from Earth at great expense, when it was already here, just floating around in the sky, in rocks like Ra.

  So he’d come back to come out to Ra-Shalom, the place that had made him briefly famous.

  He suspected the surgeons liked to have him around, as a control experiment. The youngsters were heavily treated from birth, up here, to enable them to endure a lifetime of microgravity. Not a one of them could land on Earth, of course, or even Mars. But not too many of them showed a desire to do any such thing.

  The wall spider, scuttling busily, brought him to the mine face, the terminus of Shaft Seven. It was a black, dusty wall, like a coal face. There was dust everywhere, floating in the air.

  There were five or six people here, in their brightly coloured skinsuits, scraping their way around the stalled miner. Their suits were seamless and without folds, to guard against the dust. They were all tall, their limbs spindly as all hell, their skeletal structures pared down as far as they would go.

  The miner itself clung to the walls with a dozen fat legs, with the balky rock splitter itself held out on a boom before the face. It was a radial-axial design with a percussive drill, powered by hydraulics, with a drill feed, a r
adial splitter and a loader. But for now it was inert.

  One of the youngsters came up to him. It was Gita Weissman, Mike’s granddaughter. She grinned through her translucent faceplate; her skinsuit was what they used to call Day-Glo orange.

  ‘Dust,’ she said. ‘It’s always the dust.’

  ‘Yeah.’

  ‘Grab a pump. We want to get this baby back on line or we’ll miss quota again.’

  He started to prepare a vacuum-pump tube.

  The ‘dust’ was surface rock flour: half of it invisible to the naked eye, abrasive, and electrostatically sticky. Despite their best efforts it had gotten all the way through the interior workings of Ra, coating every surface.

  A lot of Earthbound experience was worthless up here. No machine, for example, which used its own weight for leverage was going to be any use. Nevertheless, some terrestrial technologies, like coal gasification, had proven to be good bases for development of systems that gave a low capital investment and a fast payback.

  Greenberg remembered how they’d celebrated when the ore processors had first started up, and water had come trickling out of crushed and heated asteroid cinder. It had touched, he supposed, something deep and human, some atavistic response to the presence of water here, the stuff of life in this ancient rock from space.

  Whatever, it had been one terrific party.

  And this rock, and many others like it, had proven to be as rich as those old sci-fi-type dreamers, who Greenberg used to laugh at, had hoped. Ra was fat with water – twenty per cent of its mass, locked up in hydrate minerals and in subsurface ice. It exported kerogen, a tarry petrochemical compound found in oil shales, which contained a good balance of nutrients: primordial soup, they called it. Ra pumped out hydrogen, methane, kerosene and methanol for propellants, and carbon monoxide, hydrogen and methane combinations to support metal processing …

  And so on.

  Ra was just a big volatiles warehouse floating around in the sky. And with the big surface mass drivers that Greenberg called softball pitchers, Ra products were shipped to places that were volatile-poor – like Mars, lacking nitrogen, and the Moon, dry as a desert. It was a lot cheaper to export them from a rock floating around up here than from all the way at the bottom of Earth’s gravity well.