Seveneves - Страница 80

Compared with all of those complexities, the fact that Ymir would be flying backward while operating a damaged, experimental nuclear propulsion system at maximum power seemed like a mere detail.

Faced with so many imponderables, a well-managed aerospace engineering project would have called a halt to all further work and devoted several years to analyzing the problem down to its minutest detail, exposing pieces of ice to the blast of hypersonic wind tunnels, building simulations, and war-gaming possible alternative strategies. But by the time Markus understood the general shape of the problem, they had twenty-four hours remaining to perigee. The tangerine Earth had grown to the size of an orange. No power wielded by humans could prevent Ymir from passing around it and scraping the atmosphere. They couldn’t even ditch. New Caird, detached from Ymir, didn’t have enough propellant in her tanks to materially change her course and would end up going on the same ride anyway. So Markus made a reasonable guess as to what would be a good angle of attack — the orientation that Ymir would adopt vis-à-vis the atmosphere — and initiated a program of thruster firings that, over the course of half a day, swung the ponderous shard around into the position he deemed best.

Ymir’s “stern” was now aimed in the direction of movement, the huge mouth of the nozzle aimed forward so that it could make the all-important braking burn. But she was now twisted about her long axis in such a way that New Caird, still docked up near the “bow,” and projecting from the side of the shard at approximately a right angle, was on the zenith. This meant that during the passage of the high atmosphere her view of the Earth below would be blocked by Ymir, the nozzle of her engine pointed “up” toward the stars. Firing that engine would therefore tend to rotate the bow downward and the stern up, an attitude likely to produce more lift and help get Ymir out of trouble. Were the shard to tumble the other direction, it could end up in a position that would yield much more drag and much less lift, pulling the whole contraption deep into the atmosphere. In effect New Caird had been reduced to the status of a small attitude control thruster. It was a thruster that could only push in one direction, and so Markus had picked out the direction most likely to be useful if things began to go sideways. Vyacheslav would ride it out in New Caird’s pilot’s seat, from which he would enjoy an arm’s length, tunnel-vision view of some dirty, five-billion-year-old ice. He would wait for a verbal command from Markus, ensconced in Ymir’s common room, to fire New Caird’s main propulsion if needed.

All of this was mere background noise to Dinah, who was entirely consumed with coordinating the efforts of robots. The number of Nats was in the tens of thousands. They could only be talked to collectively, as swarms. Trying to address and control them one by one, while theoretically possible, was a mug’s game. Their general task was to morph the shard.

One swarm would be working on the inner surface of the nozzle bell. At the moment, all of those were out on the back end of the shard, sunning themselves to build up their internal reserves of power. At a signal from Dinah they would all converge on the circular maw of the nozzle, climb down into the bell, and spread out to reshape it as needed during the burn. They’d be running a program that Larz had developed and tweaked. So all Dinah really needed to do was to turn them on.

Likewise, the smallest of the three swarms was down inside the ice hoppers, running Larz’s program for keeping rocks away from the augers. Working in the dark, these had to sip power from electrical taps that Ymir’s crew had installed for that purpose.

The largest of the three swarms, though, was responsible for sculpting the interior of the big shard as it was hollowed out. By the time the journey to Izzy was finished, most of the ice would have been fed into the hoppers and blown out the nozzle, leaving a hollowed-out shell with just enough internal structure to hold the reactor in place and maintain some semblance of a nozzle bell. This was not as crazy as it sounded, for two reasons. First, it was what miners had done since time immemorial. They didn’t just hollow out mountains, since that would lead to collapse. They sculpted the mountains into structurally sound architectural systems, complete with pillars, arches, and vaults. This was just that, except that the material was ice, and the forces in general were not as large. Secondly, most of the shard’s interior was of little consequence from a structural engineering standpoint. There was a reason why airplanes and race cars had been hollow shells — all skin and no bones. Most structural forces were naturally transmitted through the outermost layer of the vehicle, so that was the best place to put the strength. Enough strength on the outside made it possible to leave the inside hollow.

Ice, of course, wasn’t the best material to work with. It was brittle. But the Ymir expedition had shipped out carrying a large supply of high-strength plastic cord, net, fabric, and loose fiber. And during the months that it had been coasting in from Grigg-Skjellerup, Larz’s robots had been at work converting ice into pykrete. That outer layer of visually black ice was no longer ice per se, but a synthetic material with much better structural properties. Frozen, it could stop bullets. Melted and strained, it would separate into water, artificial fibers, and black crud from the dawn of the solar system. In any case the larger robots — the Grabbs and the Siwis — responsible for doing most of the heavy material removal on the inside could scrape to within a few meters of that outer skin without compromising Ymir’s structure. It was the responsibility of the third Nat swarm to clean up after them and maintain the internal pillars and webs that would keep the reactor and the hoppers suspended in the middle of the hollow shard. This swarm-based ice-sculpting algorithm had been Larz’s invention, and he’d had a couple of years in which to perfect it, but Dinah was in charge of it now, and had a lot of learning to do between now and when she became fully responsible for it.

Outnumbered by the Nats, but responsible for moving a much larger tonnage of ice, were the hundred or so Grabbs and Siwis, now mostly stationed at the ready around the shard’s interior. Most of these were general-purpose robots with some added-on bits that made them good at moving on ice, but there were also half a dozen Leatherface machines: upsized Grabbs with shovel-studded chain saws for limbs, made to move a lot of ice in a hurry. These were so good at their jobs that they tended to destroy their surroundings, so they had to move frequently. Each one had to be followed around by an entourage of smaller robots cleaning up its mess and getting it anchored to fresh locations.

In theory it was all just a big computer program that, when executed, would smoothly convert the solid hill of ice into something like a walnut with the meat removed: a thick, pockmarked outer shell with an organic internal system of ribs, veins, and webs. As with any other computer program, it might run perfectly when Dinah started it. But it might just as well go sideways, perhaps in a manner that wasn’t obvious at first. So situational awareness was going to be a big part of her task. Interesting as it might be to look out the window and watch the Earth screaming by at twenty-four thousand miles per hour, she would need to keep her head down, searching through a roar of weak and ambiguous signals for signs that something was going awry. She liked to imagine that her days as a little girl in a mining camp, sitting in front of a radio console trying to pick out Morse code signals from far away, through static and crosstalk, might have prepared her for it in some way.

A FEW MINUTES INTO HIS SCAPE CONVERSATION WITH J.B.F., DOOB realized that, two years ago, he had done his job too well.

He’d gone into that meeting at Camp David with the mission of getting the president to understand the exponential breakup of the moon that was going to wipe out life on the Earth’s surface. Putting on his Doc Dubois hat, he had coined the terms White Sky and Hard Rain as easy-to-grasp handles on phenomena that, truth be told, were much more complicated. Dr. Harris was now wishing that the late Doc Dubois had never opened his big fat mouth.

He was in a corner of the Farm that, since the departure of New Caird, had developed into a sort of bullpen where he and Konrad and some of the other orbital mechanics geeks hung out. The Farm had always operated something like a high school cafeteria, with different cliques habitually sitting in certain areas, and now those choices were hardening, becoming a part of Izzy’s unwritten procedure manual. Anyway, they had printed out charts and plots representing, in more or less abstract form, everything that they knew about the ongoing development of the lunar debris cloud and what it might mean for the future of the Cloud Ark. The expenditure of paper and printer ink had been somewhat lavish. Two generations from now, if any humans survived, they would look on this heap of documents with some combination of disgust and amazement. Because paper was going to be scarce by then, and they would view its use for such purposes in roughly the same way as Americans of the twenty-first century had viewed the use of sperm whale oil to fuel streetlamps.

But then life would get better, forests of genetically engineered trees would grow in vast rotating space colonies, paper would become plentiful, and these sad yellowed scraps would be displayed in a museum as evidence of the privations suffered by the Arkers.