Seveneves

  Most of the fallout had, therefore, dissipated into space. But the whole point of a rocket nozzle was to convert the thermal energy in the gas—its heat—into velocity. The faster the steam went, the colder it got, until the steam near the nozzle exit was so cold that it actually began to condense into snow. Tiny particles of fallout made excellent nuclei around which a snowflake might begin to form. Some of that snow had stuck to the ice walls of the nozzle bell.

  The most likely explanation for what had happened next was that one of the robots crawling around in that area maintaining the shape of the nozzle had become contaminated with a mixture of alpha-emitting fuel fleas and beta-emitting daughters, and tracked the material to a location where it had been transferred to the glove of a space suit—possibly by a mechanism as simple as a spacewalker reaching down to brush some ice from the claw of a Grabb, or planting a foot in a location where a contaminated Grabb had stepped. The contamination had then been brought into the command module when the spacewalker came indoors. They might not even have known about the burst fuel rod, so they might not have been checking for contamination. Or, as suggested by Sean’s note, their Geiger counters might have broken down, one by one, rendering them blind to the presence of radioactivity in their environment. In any case, the particles had spread around the command module. Some men had inhaled them, some had swallowed them. They hadn’t been healthy to begin with.

  IN ANY CASE, THE GOOD NEWS, IF IT COULD BE SO CALLED, WAS THAT the reactor and the engine basically worked. The improvements Larz had made to the robots’ mining programs had led to fewer rocks in the hoppers, and fewer jammed augers, during the L1 burn. Since then, Nats had been crawling around in the hoppers identifying rocks that had sneaked in anyway, and pushing them away from the augers. The damage to the fuel rod would have been a major catastrophe by Old Earth standards—had it happened on an earthbound reactor. Here, it was messy, and had already been fatal to a few. But everything still worked. Yes, the New Caird expedition would be bringing a radioactive disaster right into the middle of the Cloud Ark, but once they drew close enough they would jettison the reactor and let it fall into the atmosphere.

  Forty-eight hours, give or take a few minutes, now remained before Earth would loom huge below them, and the nadir surface of the shard would sweat and steam as the radiant heat shining up from the incandescent air softened, melted, and vaporized the ice. It was then that they would have to pull out the control blades and execute Ymir’s next big burn. First they would have to spin the whole ship around so that she was flying “backward,” her nozzle bell pointed in the direction of movement. For the delta vee they needed was a negative one—a braking, as opposed to accelerating, burn.

  For spin moves, all spaceships were equipped with thrusters, not powerful enough to impart big delta vees but capable of rotating the ship as a whole into the desired attitude so that the main engine was pointing in the right direction. As a rule the thrusters were more effective when they were situated out toward the “corners” of the vehicle, where they could exert more leverage and crowbar the thing around with minimal thrust. Not knowing what they were going to find at Grigg-Skjellerup, the mission planners for Ymir had packed aboard a collection of modular thruster assemblies that basically consisted of little rocket engines, propellant tanks, wireless control links, and hardware for anchoring them into ice. A cursory survey of Ymir and a look at the dead crew’s records made it clear that Sean and his crew had embedded those packages into the ice at suitable locations: one complex up at the nose with nozzles aiming in four perpendicular directions, and four more spaced around the fattest part of the shard.

  Now that New Caird was docked, her engine could also be put to use in getting Ymir spun around. But this one maneuver—a 180-degree flip, which would have seemed comparatively simple in a small craft such as an arklet—was fraught with difficulties and complications in something as huge and asymmetrical as Ymir. Anticipating a need to use the thrusters, Dinah sent robots out to inspect them during that first “morning,” and Vyacheslav suited up and went out to do a bit of troubleshooting on a propellant line that had somehow become kinked. But so ponderous were the shard’s movements that the actual rotation, end-over-end, consumed eight hours, and tweaking it into precisely the right orientation then took another six.

  Whereupon Markus announced that all of their assumptions were probably wrong anyway.

  “The atmosphere is too big,” he said. He had been staring pensively, for a long time, at a string of emails from Izzy.

  Dinah felt a spear go through her heart. After all that had happened in the last couple of years, it was remarkable that she still had it in her to react in that way to bad news. It seemed to be some kind of built-in psychological program, triggered by phrases like “your mother has cancer,” “there’s been an explosion in the mine,” or what Markus had just said.

  They had known, from very early in the planning of the Cloud Ark, that the Hard Rain would heat up the air—all of the air, all over the world. When air got hotter, it expanded. The atmosphere had only one direction in which it could expand: out into space. So, whatever drag Izzy felt from the traces of air at its accustomed altitude of some four hundred kilometers was bound to get worse as the atmosphere reached upward. How hot the air would get, how much it would expand, and how heavy the drag would get were questions of colossal import that, however, simply could not be answered until the Hard Rain actually started. As Doob always put it, the experiment of blowing up the moon had never been attempted before. The most they could do was wait and perform observations. Which was exactly what they had been doing ever since the Hard Rain had begun. But Markus had been distracted for most of that time, and was only now absorbing the latest results.

  For the Cloud Ark, of course, there were plans to cover various contingencies. In the easy case where the atmosphere didn’t expand that much and the drag wasn’t too bad, they didn’t have to do much. In the more difficult case—which was apparently the way the experiment was now shaping up—they had no choice other than to raise the orbit of every vessel they had—Izzy herself, and each arklet. The delta vees involved were not that large; three hundred meters per second sufficed to nearly double the orbital altitude and get them well clear of the danger zone. Each arklet had its own engine and enough of a propellant supply to accomplish that. For Izzy, matters were a little more complicated. If they were willing to ditch Amalthea they could get three hundred meters per second pretty easily. Bringing Amalthea along for the ride, however, increased the propellant requirements enormously. All of which had long ago been anticipated by mission planners. This was how the Dump and Run strategy had been dreamed up in the first place.

  So it would be easy for the arklets to get clear of the thickening atmosphere by abandoning Izzy, at least for the time being, and jumping to higher orbit. Their drag problems would be solved. But in so doing they would lose the ability to shelter behind Amalthea and begin to take damage from bolides. Exactly how much damage depended on how thick and fast the rocks were coming in, and what the distribution of sizes was—another one of those questions of colossal import that couldn’t be answered until the Hard Rain had actually started and data had been gathered.

  And, so far, the data were too thin to make any real determination. With a few spectacular exceptions, bolide impacts and casualties had been light. But this didn’t mean it would remain thus. The White Sky was an ever-changing phenomenon. The explosive uptick in the Bolide Fragmentation Rate that had signaled its onset was still ongoing. The distribution of rock sizes and orbital parameters would continue changing for thousands of years. Trends could be observed, and predictions could be made, but beyond a certain point it was guesswork.

  At any rate, Markus had rolled the dice on the gambit that they were now executing. If it worked, and they could slow Ymir down enough to mate her with Izzy, then the Big Ride strategy became possible, and the arklets could climb to higher and safer altitudes behind the shelter of Amalthea’s me
tal and Ymir’s ice.

  The one part of that plan that Markus apparently had not considered until now was that the atmosphere was too big.

  In truth, it wouldn’t have made a difference if he had considered it. The crucial decision had been made and executed weeks ago by Sean Probst, when he had laid in a course at L1 and executed the burn that had placed Ymir on its current trajectory. This was an ellipse with a very low perigee. That was a sound idea from an orbital mechanics point of view in that the steam engine would have maximum leverage at that point—it was the natural place to make a burn and effect a transition to a low circular orbit matching Izzy’s. But, sick and exhausted from his two-year odyssey, isolated from the latest scientific discourse by radio failure, Sean might have overlooked the expansion of the atmosphere when making his calculations.

  “Are we going in?” Vyacheslav asked. This being a polite euphemism for the scenario where Ymir got so deep, and slowed down so much, that it burned up and became just another streak of blue light against the lambent background of the pyrosphere.

  “We are more likely to skip, I think,” Markus said. Meaning that Ymir might bounce off the atmosphere like a flat rock skimming across a pond. “With unpredictable results. But I cannot be sure. All I am saying is that this is not going to be the mission plan that Sean had in his mind. It is going to be something else. Something maybe a little more exciting.”

  ANTICIPATING THAT CAMILA MIGHT BE ON HER TOES—SHE HAD ALREADY survived one attempt—the gunman had crouched behind the rear of her school bus, sawed-off shotgun at the ready, and waited for her to emerge. A narrow stretch of pavement separated the vehicle’s side door from the entrance of her school, so he didn’t have much margin for error. He jumped the gun, as it were, springing out into the open while Camila was still negotiating the descent to the street; the long hem of her burqa was apt to get caught on her foot as it probed for the running board, so she had to take it slowly. The delay saved her life. Alerted by a schoolteacher standing in the building’s doorway, Camila turned back into the bus. Rather than hitting her full in the face, the shotgun blast raked the left side of her jaw, removing eleven teeth, tearing away much of her cheek, and causing massive structural damage to her jaw. Surgeons in Karachi and, later, London had saved most of the functions of her tongue, rebuilt her mandible from pieces of bone carved from her pelvis, and fitted her with a set of artificial teeth. After a world tour raising money for girls’ education in Afghanistan and the tribal regions of Pakistan, Camila had been granted permanent asylum in Holland. Dutch plastic surgeons, funded by charitable donations from all over the world, had gotten to work repairing the cosmetic damage. This was a long-term project that had been interrupted by Camila’s selection as one of the Dutch candidates for the Cloud Ark. No one believed that this was a random outcome of the Casting of Lots. Clearly the Dutch authorities had placed their thumb on the scale and seen to it that she was chosen, as a rebuke to some conservative Muslim countries who had refused to nominate female Arkers unless given assurance that arrangements would be made for them to live in orbital purdah. Camila was well suited to serve that symbolic purpose, since she had not adopted Western ways. She dressed conservatively and wore the head scarf and the face veil. She was coy, however, as to whether the purpose of the face veil was submission to the demands of religion or to hide her disfigurement. She had pulled it down several times to display the scars to television cameras, and when she had dined at the White House she had gone uncovered in the dining room, by prearrangement with her hostess, the president of the United States.

  Julia’s startling arrival in the Cloud Ark had therefore led to a reunion between the forty-four-year-old ex-president and the eighteen-year-old refugee. To call it joyous or even happy would have been wrong given the circumstances. It was a fact of human nature, though, that some people just got on well with each other. This had clearly been the case during that dinner at the White House and was no less true in Camila’s abode, Arklet 174, which was where Julia ended up lodging after she had recovered from her eventful flight up and gone through a bit of basic training in how to live in space.

  Arklet 174 belonged to a heptad, or a cluster of seven arklets all connected to a hexagonal frame; it and five other arklets surrounded a seventh, which was positioned in the middle of the hexagon, where it served as a twenty-four-hour-a-day common room and working area for the people who lived in the others. Four to five people were assigned to each of those, and two more had been shoehorned into small private cabins at the boiler room end of the central arklet, so the total population of the heptad, including Julia, was twenty-nine. This increased to thirty when Spencer Grindstaff managed to hitch a ride on a Flivver that was bringing a spare part and a technician from Izzy to fix a problem in one of the arklets’ thrusters. The technician returned to Izzy when he was finished, but Spencer stayed, and talked his way into a berth on Arklet 215. There was a tendency for arklets within a group to become segregated by sex over time, as the populations sorted themselves out; 215, which was predominantly male, ran on the same shift as 174, which was all-female. They both ran on second shift, which, for reasons that were now purely historical, tended to be culturally American. They slept from dot 8 to dot 16. First shift was Asian and third shift was European. The cultural shadings were perpetuated by food: the warm odors that greeted one’s nostrils upon entering the common space first thing in the “morning,” the tastes one could expect to savor in the “evening.” Since space food was lacking in variety, this was largely a matter of spices. The second shifters had their little bottles of Tabasco, the first shifters had plastic packets of curry powder, and so on.

  “Ganging” was the term used by the Arkitects to denote this clustering of arklets into formations of three or seven: triads and heptads. It helped simplify Parambulator’s job by reducing the total number of separate objects that needed to be tracked. It gave Arkies more living space to roam around in, and provided some redundancy in the case of a bolide strike. They didn’t like to form anything larger than a heptad, though.

  “Spencer, I am fully aware that I am out of my depth here,” Julia said, “but I don’t understand the upper limit of seven. I was assured, during my early briefings, that any number of arklets could in principle be ganged. Limiting it to seven seems arbitrary. Which suggests that some deeper agenda might be behind it.”

  “One moment please, Madam President,” Spencer said. He was doing rather a lot of typing.

  “You really shouldn’t call me that,” Julia returned, though her tone of voice was indulgent.

  Spencer smacked his laptop’s Enter key, then leaned back slightly and adjusted his glasses. His eyes jumped around to various parts of the screen. Then he looked up, and, in a clearer tone of voice, announced, “It’s all shut down.”

  “The surveillance, you mean.”

  “Situational Awareness Network,” he corrected her, and winked.

  “Surveillance to you and me. It’s like living in the Nixon White House. Old reference. You wouldn’t understand. Now, where was I?”

  Camila knew. She hadn’t taken her eyes off Julia the whole time; she was on top of it. “The agenda behind the seven-arklet limit?”

  “Yes, thank you, Camila. I don’t buy their arguments. To me it feels, rather, like a way of atomizing the population. Keeping the Arkies from cohering into their own polity—a polity that might serve as a wholesome and desirable counterweight to the central dominance of the power structure on Izzy. Speaking of which, Spencer, I want to say how much I appreciate the work you have done in . . . managing things . . . on the IT front. As just now. Giving us the freedom to talk among ourselves without the SAN recording our every word and gesture.”

  Spencer nodded as if to say all in a day’s work.

  It was dot 18, the beginning of the workday for second shifters. They were in Arklet 215, home to Spencer, three other men, and a woman. The others had gone to breakfast in the common area, to exercise, or to work. Spencer, Julia, an
d Camila had been joined by a guest: Zeke Petersen, who had arrived by space suit and was still clad in his thermal coverall. He looked mildly agog. Sensing this, Julia turned toward him with a smile. “Major Petersen,” she said, “it is so good you were able to join us. Though I am new to space, I have some understanding of how difficult it is to simply drop by and say hello, as it were.”

  “Well, technically I am no longer a major, since that would imply the existence of a military,” Zeke said, “but if we are going to use extinct titles as a courtesy, then I’ll just thank you for your hospitality, Madam President.”