Seveneves

by Neal Stephenson

  Finally there was a third “crew” of robots living on the exterior surface of the shard, trying to keep it from falling apart by embedding fibrous reinforcement in the outer layer of ice and wrapping cables and nets around it, somewhat like a butcher tying up a roast to prevent it from collapsing in the oven. This was a good match for the capabilities of the Grimmed (steel-armored) robots, which were mostly Grabbs.

  All of these robots needed power, of course. They could store a little of it in batteries, but those had to be recharged. Some of them collected energy from sunlight; others had to converge from time to time on one of Ymir’s little nuclear generators to sip electricity.

  The general picture was that Ymir would not be anything like the traditional idea of a spaceship, in the sense of an orderly, symmetrical piece of architecture. It would be more like a flying robotic anthill, constructed out of a natural found object. The robots crawling around on and in it had general instructions as to what they were supposed to be doing, but could make their own judgments from moment to moment to avoid collision with other robots, or from hour to hour as to when they needed to recharge their batteries.

  Or that had been the general scheme, anyway. Since there’d been no guessing what Sean would find, there’d been no way of coming up with any plan worthy of that name. Instead they had sent him up with tools, resources, and ingenuity. Dinah, Markus, Vyacheslav, and Jiro were about to inherit the tools and the resources.

  Jiro’s Eenspektor made steadily more noise as they approached, but the growth was slow enough that their minds didn’t quite register it. Jiro did not seem alarmed by the level of radioactivity, but Dinah didn’t know how to interpret that. Earlier in the mission, she had probed him for some general background about what to expect. “If it’s very bad, we all just lose consciousness and the mission fails,” he’d said. “The flux of radiation just shuts down our nerves, our sphincters open, we never even know it’s happening.”

  “In that case,” Markus had pointed out, somewhat testily, “there is little point in discussing that scenario.”

  “If all four of us throw up,” Jiro had continued, “and, say, one or more of us gets diarrhea, then we have hours to live. In that case we should just transmit a warning to Izzy and encourage them to send a second mission. In the meantime, maybe we can transmit some useful information to them. Eenspektor data, pictures, et cetera.”

  “Noted,” Markus had said.

  “If, say, one of us throws up, then it means that half of us will probably die, and so we have some chance of accomplishing the mission. If no one is barfing, then none of us is likely to die, at least over a time span of weeks.”

  “Thanks for that,” Dinah had said, and tried to put it out of her mind. Now that they were actually approaching Ymir, however, it was coming back to her, and she was trying to convince herself that she wasn’t feeling any nausea.

  “I am going to traverse the nozzle mouth in about thirty seconds,” Markus announced.

  “Roger,” Jiro said, and then switched off his Eenspektor altogether. He pulled up a window on the screen of his tablet. “Switching to the external gamma spec now.”

  Suddenly Ymir was filling the window. It was dead ahead of them. The glowing Earth, a third of a million kilometers away, “set” below its black horizon as they sidled in behind it. Markus had placed them on a trajectory that would slowly cross that of Ymir, bringing them laterally across the ice ship’s aft end.

  Dinah’s older relatives might have described Ymir as having a sugarloaf shape, meaning a cone with a blunted tip. If so, this sugarloaf had been splashed with boiling water and attacked with a screwdriver in several places, giving it a scarred, irregular form. But it clearly had a fat end and a narrow end. These were about half a kilometer apart. The fat end, which was beginning to swing across their field of view, was a couple of hundred meters wide. It had a big circular hole in it, which was the outlet of the ice nozzle. New Caird could have flown into that hole and followed it almost all the way up to the throat before running out of room. And perhaps they would do so later, if they could find no other way in. But for now they were just going to make a lazy swing across it. The edge of the hole was blurry because of the evanescent steam cloud leaking out of it. This looked not so much like rocket exhaust as like breath emerging from someone’s mouth on a cold day. It didn’t so much block their view as soften it. But the visual landscape of space was one of intense contrasts, and so it was impossible to see down into the nozzle bell, even when they were squarely in the middle of the cavernous hole. It was just a black disk—like staring into the muzzle of a rifle. Hair-thin needles of frost grew on the window as the steam condensed.

  Jiro focused intensely on his tablet until they had drifted past the midway point, then seemed to draw back into himself. He switched his Eenspektor back on. It was making a lot more noise than it had a few minutes ago, but this gradually diminished as they traversed beyond the nozzle exit and across the wide base of the sugarloaf. With a tap on the thrusters Markus got them moving forward with respect to Ymir. Earth “rose” on her other side. New Caird moved up alongside the shard, headed for her forward end.

  “What’s the verdict, Jiro?” Markus asked, when he was satisfied with how things were going.

  “Based on the gamma spec,” Jiro said, “I would say that at least one of the fuel rods ruptured. Not at the beginning, when the rods were new, and not recently, when they were full of fission fragments and daughters, but somewhere in between. Could be worse, could be better.”

  A memory came back to Dinah. “One of Sean’s last messages said he was thrusting at full power.”

  Jiro shrugged. “This reactor contains sixteen hundred fuel rods, grouped in assemblies of forty, so the failure of a single rod wouldn’t measurably affect performance. Even the ruptured rod still makes power, remember. It’s just that it would be spewing fuel fleas, fragments, and daughters into the rocket exhaust. We would expect to see a mixture of alpha, beta, and gamma—which is just what the Eenspektor is reporting.”

  Dinah was no nuclear physicist, but she’d had enough radiation facts drilled into her to get the gist. Gamma was high-energy light. It would pass through just about anything. So, bad news, good news: It was hard to shield against the stuff. But most of it passed right through your body without interacting—that is, without doing damage. It made scary noises on the Eenspektor.

  Betas were free-flying electrons. They were easy to shield against. Good news, bad news: You could stop them with a little bit of water or plastic. But by the same token, if they came into contact with your body they were certain to break something inside of you.

  Alphas were helium nuclei, four thousand times as massive as betas, moving at relativistic speed. They could not pass quietly through matter any more than cannonballs could, but they did a lot of damage to whatever they hit.

  In order to detect anything other than gamma, Jiro had been forced to switch over to equipment mounted on the outside of New Caird, since alpha and beta couldn’t penetrate the hull. And by looking at the energies of the various particles striking that equipment he had been able to diagnose conditions inside the reactor.

  Since she could no longer see Ymir out the front window, Dinah focused on the slivers of frost that had grown on the glass. These were rapidly sublimating into space, and would be gone in a few more minutes. She’d found them beautiful until Jiro had made them aware that they were probably contaminated.

  “Any residual beta now?” she asked.

  “We are well clear of the nozzle and the plume,” Jiro said, a little taken aback.

  “I mean, did we pick up any contamination on that flyby?”

  “It is back down to background levels,” Jiro said. “But the detector would only ‘see’ sources on its side of the hull. We will have to do a more thorough survey later.”

  “Get a load of this,” Markus said, and punched in a maneuver that swung New Caird around ninety degrees. They were now flying “sideways,”
their nose aimed directly at Ymir, which was only about a hundred meters away from them. She more than filled the window. Her narrow end—her bow, if you wanted to think of her as a ship—was a hill of dirty ice. A few fine structures suggested that humans had been at work there: some structural netting, some cables, a glinting wire that might have been the radio aerial. But it wasn’t obvious, yet, where they were actually going to dock.

  “It is really buried,” Markus observed. He didn’t have to explain that “it” was the command module—the part of Ymir that had life support systems. It ought to be reachable through a docking port. But they weren’t seeing anything. They had known—because it was part of the plan—that Sean and his crew would have buried it in the ice, to protect them from radiation and from rocks. They looked to have buried it deep.

  Dinah’s tablet was running a terminal window, a simple programmer’s interface that just displayed lines of text. For the last little while, this had shown only a blinking cursor, but now it came alive and began to display cryptic, one-line messages.

  “Picking up some new bot sigs,” she reported. These were the digital signatures of robots, pinging the universe to find out what, if anything, was listening. New Caird had shipped with a complement of robots of various types, but she knew all of their sigs and was filtering them out of this terminal window. Anything that showed up here was, by process of elimination, from Ymir’s complement of robots.

  Like the clicks on Jiro’s Eenspektor, these came up sporadically and in bursts.

  “At least twenty . . . so I am going to filter out the Nats,” she said, typing in a command. Being so numerous, Nats tended to overload the screen. “Okay, in addition to a pretty well-developed Nat swarm I have half a dozen Grabbs and at least that many Siwis.”

  “Any clues in their names?” Markus asked. It was possible to give each robot a unique name, which would show up on its sig. By default these were just automatically generated serial numbers, but they could be manually changed.

  “Well,” Dinah said, “here is a Grimmed Grabb whose name is ‘HELLO I AM RIGHT ON TOP OF THE DOCKING PORT,’ which seems promising.”

  “Can you make it flash?”

  “Hang on.” Dinah established a connection to HELLO I AM RIGHT ON TOP OF THE DOCKING PORT and, after quickly checking its status, told it to blink its LEDs until further notice. Before she even looked up from her screen she could tell, by subvocal exclamations from the others, that it had worked.

  “I see it very clearly,” Markus said. Some pops and bangs sounded from the thrusters as he adjusted New Caird’s attitude. They were now flying in nearly perfect sync with Ymir, looking at the flashing Grabb from a distance of maybe five meters. It was anchored into the surface of the shard in an area that was relatively free of the black stuff.

  “Aim the light down into the ice, please? And put it on continuously?” Markus requested.

  The Grabb’s LEDs were mounted on snaky stalks that could be aimed. Dinah made it happen. When next she looked up through the window, she could see the silhouette of the Grabb centered in a nimbus of white light, produced by its aiming its lights directly into the ice. A sharp white disk was visible in the center of that silvery cloud. It was blurred by the ice, but they all recognized it for what it was: a docking port, buried at least a meter deep.

  “Did anyone bring an ice pick?” Jiro asked. It was not like him to make a joke, but Dinah was happy to take humor from any quarter at this point.

  “Slava,” Markus said, “you’re up. Dinah, maybe you can help by bringing more of the robots to the area.”

  By entering a fairly simple command, Dinah was able to summon every Grabb and Siwi in range, telling them, in effect, “Figure out a way to get closer to HELLO I AM RIGHT ON TOP OF THE DOCKING PORT and don’t bother me with the details.” By the time Vyacheslav was suited up, enough of these had drawn near that she was able to clinch several of them together and form a temporary construct that “reached” up from the surface of the ice to grapple New Caird, first in one location and subsequently in two more. So, even though they had not been able to dock yet, they at least had a mechanical link to Ymir that would prevent them from drifting away.

  Other robots, including HELLO, meanwhile busied themselves carving a hole in the ice “down” toward the buried docking port. Vyacheslav exited through New Caird’s airlock, clambered down a stack of robots to the surface, and then made his way toward the site. Since the gravity of Ymir was negligible, Vyacheslav’s “weight” here was about half a gram, and the faintest contact with the surface would send him rebounding off into space. So instead of walking he had to rely on some sort of anchor fixed into the ice. Dinah was able to send two of New Caird’s Grabbs scuttling along ahead of him. These had been engineered for movement on ice, and could rapidly anchor themselves by melting and refreezing it with their footpads. All Slava had to do was follow them and hold on to them. Once he had reached the mouth of the hole he was able to embed anchors and carabiner himself into place. Then he speeded up the work of the robots by scooping out more ice, more quickly, than they were capable of moving with their little claws.

  Not knowing what to expect, they had brought with them a small arsenal of improvised ice-mining tools, including a Craftsman garden shovel that had mysteriously made its way up from a Sears, Roebuck in an Old Earth mall. Slava put it to work.

  Meanwhile Markus was sending a status report back to the Cloud Ark, and Jiro was doing more typing than seemed necessary just for taking notes. He was communicating with someone, or, more likely, something. Dinah was tempted to ask what, but there was only one plausible answer: he had established contact with the computer that controlled the reactor core.

  Markus seemed to have come to the same conclusion. “Jiro?” he asked. “News from the belly of the beast?”

  “It’s alive,” Jiro said, in what might have been either awkward phrasing, or a second consecutive joke. “I am trying to make sense of the logs. There is a lot of repetitive material.”

  “Error messages?” Markus asked, making the obvious guess.

  “Not so much. It is robot stuff. Status reports.”

  Dinah moved over one seat and had a look. Though she couldn’t tell exactly what was going on, her general read tallied with Jiro’s. Lots of robots had been working away, executing variations on the same small set of programmed behaviors, pumping out occasional status reports—and, yes, some error messages—that had generated a log too vast for any human to read. They would have to sort it out later by writing a computer script that would crawl through it, accumulating statistics and looking for patterns.

  “Could you scroll to the top, please?” she asked. She wanted to know the date and time of the first log entry.

  “I checked it,” Jiro said. “Right around the time of Sean’s last transmission.”

  So Sean, probably knowing that he was at death’s door, had told the robots to do something, and to keep doing it, until they were ordered to stop. Since the outer surface of the shard was pretty quiet, this probably related to some internal work hidden beneath the surface. “Mining fuel, probably,” Dinah guessed. Then, before Jiro could object to the incorrect choice of words, “Propellant, that is.”

  Vyacheslav exposed the docking port. Using a combination of taps on New Caird’s thrusters, some pushing and pulling by the robots, and Vyacheslav simply grabbing the spacecraft and nudging it this way and that, they inserted her “front door” docking port into the little crater that Vyacheslav and the robots had excavated, and mated it with that of Ymir’s buried command module.

  Slava then had to reenter New Caird through its side airlock. By sounds conducted through the hull they could track his progress as he climbed into the chamber, closed the outer hatch, and activated the system that would fill the lock with air.

  In the meantime, Markus was able to make contact with the computers on the other side of the port, and verify that there was breathable air and other amenities.

  It was damn
ed cold, though: about twenty degrees below freezing.

  “That was Sean doing us a favor,” Markus said. “He turned the thermostat down before he died. His body will be frozen solid.” For Ymir had no lack of power from its nuclear generators, and its electrical systems were still working.

  Markus entered a command that would turn the command module’s environmental systems back on and bring the temperature back up. He pressurized the tiny space between Ymir’s hatch and New Caird’s. Then he opened the latter.

  They were all looking now at the slightly domed exterior surface of the hatch that would lead into Ymir’s command module.

  Someone had written on it with a felt-tipped marker. He had drawn the trefoil symbol used to warn of radiation hazards and beneath it had written the Greek letters alpha, beta, and gamma. Then, as a darkly humorous doodle, he had added a crude skull and crossbones.

  Markus was the first to recover. He spiraled out of the pilot’s chair and propelled himself aft to the inner hatch of the airlock. There he punched a virtual button on a screen, which had the effect of locking the inner hatch. He was not letting Vyacheslav come in. He reached up with one hand and adjusted his headset. “Slava,” he said, “can you hear me? Good. Listen. We have contamination. You may have picked some of it up on your space suit. Before you come inside, I would like you to go over to Jiro’s external radiation detector and see if we pick anything up.”