Jiro was already scanning the hatch with his Eenspektor, fortunately without results.
Outside they could hear Vyacheslav cycling the airlock again and clambering back out. Using external handholds on the hull he made his way to the place where the external gamma spec was mounted, and devoted a couple of minutes to turning this way and that, directly in front of them, paying particular attention to his gloves, his knees, his boots—anything that had come into contact with the ice. No bursts of radiation were noticed, and so he was given clearance to go back to the airlock and enter New Caird.
They had brought warm clothes, which seemed advisable when going on a journey to a huge piece of ice. Jiro put his on. Dinah reached for the stuff sack in which she had stored hers, but Markus held up a restraining hand. She noticed he was making no effort to dress for the occasion. Jiro was going down there alone.
“I am going to overpressurize us a little bit,” Markus said, working with an interface on his pad. Dinah felt pressure building against her eardrums. Markus didn’t explain himself, and didn’t have to: they wanted clean air from New Caird to waft into Ymir, as opposed to potentially contaminated air coming in here.
Jiro then pulled a disposable one-piece bunny suit over his cold-weather gear. For they had come prepared to find the ship contaminated. He slung his Eenspektor over the outside of the bunny suit. Dinah handed him a respirator mask, so that he wouldn’t breathe radioactive dust into his lungs, and he pulled it on over the bunny suit’s hood and checked it for a good seal against his face. He pivoted into the space between the ships, operated the external latch on Ymir’s hatch, and jerked forward slightly as the overpressure in New Caird pushed it open. He let himself drift into the command module, then got himself turned around so that his feet were oriented toward the “floor.” Meanwhile Markus pulled the hatch closed behind him.
Vyacheslav by now had emerged from the airlock. He, Dinah, and Markus were listening to Jiro’s breathing on their headsets.
“Sean bled to death,” Jiro announced.
YMIR’S COMMAND MODULE WAS ARKLET-SIZED. OF COURSE, THAT went for almost everything now in space, since an arklet was just the biggest object that could be launched into orbit on the top of a heavy-lift booster. Some arklets were “tunnel,” meaning that they were laid out in a “horizontal” orientation, meant to lie flat, as it were, like railroad tank cars, with a single long floor running from end to end. This was good if you wanted a large open space, but tended to be a less efficient use of available volume. The command module of Ymir, like that of New Caird, was “silo,” meaning that it was oriented in a “vertical” way, diced into a number of round stories—typically four or five—joined by a ladder. Each story was a fat disk of space about four meters in diameter, big enough for one room that would be considered large by space travel standards, but more often divided into smaller compartments.
Ymir was a five-story silo, meaning that it had low ceilings that must have made it a claustrophobic place in which to spend a two-year journey. The first story Jiro had entered, being closest to the surface with its cosmic ray and bolide hazards, was a single room. On the plans, it was supposed to be used for storage of things like food, scrubber cartridges, robot parts, and tools.
After a few minutes Jiro was able to set up a video link from a camera mounted to his head. They watched it on their tablets.
The frozen body of Sean Probst was floating in a sleep sack that had been zip-tied to the ceiling. The porous fabric was stained dark brown. Very little of it had not been soaked with blood.
Bumping lightly against him was an old-school Geiger counter, tethered by another zip tie. The word BUSTED had been written on it with the same felt-tip pen used to make the sign.
After sweeping Sean’s body and the rest of the level with his Eenspektor, Jiro floated down the gangway to the next level “down.” The noise of the Eenspektor built steadily.
“Oh, turn the fucking sound off,” Markus said, and it went quiet. It would now display the counts per minute on its little screen, which only Jiro could see, but they wouldn’t hear the clicks.
The next story was a sort of general meeting, dining, and muster room, mostly open space lined with storage lockers. The third, or middle, story was divided into sleeping compartments, toilets, and showers. The fourth was a laboratory and workshop space. Those functions continued down into the fifth and bottom-most story.
“Cold here,” Jiro said, as he reached the bottom level. “Suddenly a lot of beta.”
“Okay,” Markus muttered, “so the contamination is there. On the fifth level down.”
It was cold, as they soon saw, because someone had left the door open: a manhole in the middle of the floor, big enough for a person in a space suit to climb through it and into a round shaft leading straight down into the ice. The entire length of the shaft was illuminated by white LEDs.
“That is remarkable,” Markus said.
Jiro descended into the tunnel headfirst and began to propel himself along it by the simple expedient of pulling on a knotted rope that had been fixed into its wall by ice anchors. He moved tentatively at first, then more rapidly. “There is a hatch at the far end—a hundred meters away, maybe,” Jiro said.
“Radiation?” Markus asked.
“Not so much,” Jiro said. “I do not think this was the route of the contamination.”
The hatch at the end was adorned with a more formal rendering of the radiation hazard symbol. They all knew what was on the other side of it: a small pressurized module that was physically connected to the guts of the reactor. Jiro elected not to go through, instead turning around for a return to the command module.
Then he turned back suddenly, and swept the beam of his headlamp across the ice wall of the tunnel. Some long slender object was embedded in the ice.
Two long slender objects.
Two human bodies. Dinah gasped as she recognized Larz’s strawberry-blond hair.
Without making any comment, Jiro made his way back “up” the tunnel to the lower level of the command module. He turned his attention to a locker near the hatch. Its door was open. Mining tools and space suit parts were floating around in it. Others had spilled out into the room and were drifting around aimlessly, pushed by currents of air.
“Jiro,” Markus said, “talk.”
“Strong beta from here,” Jiro said. “This is where the contamination came from.”
He drifted back up to the common room and found a garbage bag in a cabinet, then returned to the bottom level and went to work sorting through the tools and the clothing, holding each of them in turn up to the Eenspektor as he focused on its screen. From time to time he would grimace at the results and push the item into the garbage bag.
Dinah, Markus, and Vyacheslav waited in New Caird for an hour, pretending to pass the time with tasks on the screens of their tablets.
Then they heard Jiro’s voice again: “Prepare to put something out the airlock!” he was shouting.
It took them all a few moments to understand Jiro’s thinking. New Caird and the command module of Ymir now formed a closed system. Since the latter was completely embedded in ice, the only way to remove something from that system—to take out the radioactive garbage—was to put it out New Caird’s airlock.
There were some distant thuds. Dinah floated forward and opened the hatch to be greeted by a garbage bag, filled to the dimensions of a beach ball, and all wrapped up in duct tape. Propelled by a shove from Jiro, this entered New Caird. Dinah pushed it up to Markus, who intercepted it and tapped it sideways into the airlock. Vyacheslav slammed the hatch behind it. Then they heard a hiss, indicating that the lock had cycled. The bundle was now adrift in space.
Jiro’s head, then the rest of him came through the port. He had stripped off the bunny suit and the respirator and presumably stuffed them into the garbage bag. He was sweaty and exhausted.
“Just like old times, my friend?” Markus said, referring to Jiro’s earlier career running cleanup
at Fukushima.
“I don’t miss it,” Jiro said.
It was warm in the command module now, so they didn’t need the parkas. But they all used bunny suits when they went into Ymir, and stripped them off before going back into New Caird. Contamination was “sneaky,” as Jiro put it. The beta emitted by a microscopic speck of fallout could be hidden from the Eenspektor’s view by just about any random obstacle—and the command module was cluttered with those. So Jiro’s initial sweep was no guarantee that tiny beta-emitting particles weren’t still hidden in there. If such particles found their way into a lung, or the digestive tract, fatal radiation damage was likely to result. He had, though, identified a space suit glove on the lower level as being heavily contaminated, and found lower levels of contamination on some other odds and ends that had gone into that garbage bag and out the airlock. With luck all serious sources of contamination had now been removed.
BEFORE IT HAD TIME TO THAW, VYACHESLAV TOOK SEAN’S BODY down from the ceiling. Slava wasn’t a life scientist, but he was a jack-of-all-trades. Bundled up in parka and moon suit, he cut the sleep sack open as Jiro stood over him with the Eenspektor. He performed a cursory exam, then wrapped the body back into the sleep sack. He maneuvered it to the lower level, threaded it through the manhole in the middle of the floor, and then pushed it down the tunnel to the end, where Larz and the other crew member had been buried. There, he stashed Sean’s body against the ice wall.
Somewhat ruining their appetite, he reported on the findings of this impromptu autopsy as they got ready to eat a meal in the common room.
“Sean bled to death out of his asshole,” he reported. “He had an internal rupture of the bowel.”
“I picked up some beta through his belly,” Jiro added. “He was very emaciated at the end.”
“Meaning?” Markus asked.
“He swallowed a particle of fuel. Probably a fuel flea that got loose and somehow was tracked in here.”
“Fuel flea?” Jiro had used the term before. No one else knew what it meant. It had gone in one ear and out the other, just another bit of the tech jargon that was so ubiquitous on Izzy. Now that fuel fleas were killing people, it was time to learn about them.
“A tiny piece of uranium or plutonium that has gotten loose from a ruptured rod. As it throws off alpha particles, it zigs and zags around the room—conservation of momentum. So it hops around like a flea. The point is, it is small and it makes a lot of alpha. It lodged in a diverticulum in his bowel. It burned through his bowel wall and started a bleed that could not stop.”
Everyone pushed back their food.
“Okay,” Markus said. “We eat in New Caird.”
Once they had finished their meal, Markus told everyone that they needed to sleep, since they had a busy few days ahead of them. Jiro volunteered to take the first watch, and so the rest of them slept while Jiro stayed up going through logs and notebooks, assembling a picture of all that had happened on Ymir’s journey.
Suddenly they had a lot of space to spread out in. Dinah was tempted to retreat to the far end of the New Caird and get some privacy, but Markus insisted that everyone sleep down in the command module. New Caird might be free of radioactive contamination, but it was exposed to the direct hazards of space. A bolide strike would kill anyone in it. Whereas a beta-emitting particle, inhaled into the lung, would take days or weeks to incapacitate the victim—time during which they could do useful work.
So Vyacheslav ended up sleeping in one of the berths on Ymir’s crew accommodation level, while Dinah and Markus shared another. Somewhat to her surprise, they actually managed to have sex, a thing that had occurred only once since the White Sky. It was a sly surprise, not the athletic banging around that they had enjoyed the first few times they had done it, back in the good old days when the Hard Rain had seemed far in the future and the Cloud Ark had still felt like an isolated research colony. Ymir, now separated from the rest of the human race by millions of kilometers’ distance and several thousand meters per second of delta vee, now had some of that old feel to it. And despite the ghoulish scene that had greeted them on arrival, Dinah liked it here—it was the space equivalent of one of Rufus’s old mining camps—and didn’t really want to go back.
But they were supposed to be saving the human race, not enjoying an exotic holiday, so she tried to get some sleep. When Markus’s alarm went off five hours later she peeled out of the bag they’d been sleeping in and did her best to clean up and get into some fresh clothes. Ymir had long ago turned into a smelly bachelor pad, short on toiletries, and, as they discovered while rooting around in the common area, on food. Sean had definitely been killed by the fuel flea in his gut, but he had likely been weakened before then by malnutrition, and even by lack of oxygen. For the systems that the crew had been using to replenish Ymir’s air supply were not in the best condition. The new arrivals were awakened twice during their sleep cycle by alarms from the life support system, which Jiro silenced and dealt with.
When they were all awake, they ate food from the stores they had brought with them and listened to a briefing from Jiro.
“Let me tell you what happened to this expedition,” he said. And then he told them the story as he had pieced it together from the logs left behind by the dead.
The failure of the radio, shortly after the beginning of the mission, had been caused by a defective part for which there was no replacement: a simple, stupid oversight. The longest leg of the trip—the year and a half spent coasting from the L1 gate to Grigg-Skjellerup—had consisted of lengthy stretches of boredom interrupted by occasional panics, most of which had to do with the life support system. This was based on using sunlight to grow algae, a process that worked well in the lab but had turned out to be difficult to sustain on Ymir. The newest arklets in the Cloud Ark had benefited, in this respect, from lessons learned operating such systems in the time since Zero, but Ymir had been built and launched very early, using systems that now seemed painfully out of date.
Once they had reached “Greg’s Skeleton” and thereby gotten access to vast amounts of water, they’d been able to make oxygen by splitting H2O, and life had improved. Until then, however, they’d been oxygen hungry and tense, trying to keep their consumption of air and food to a minimum by floating listlessly in their sacks watching the same DVDs over and over again. Health, and mental status, had suffered.
They broke the shard from Grigg-Skjellerup using small mining charges planted by hand, or by robots programmed by Larz. Into its nose they embedded the command module, making themselves comparatively safe from cosmic radiation and bolides for the first time since the beginning of the mission. Life began to improve. They started excavating the access tunnel into the core. Into the aft end of the shard they inserted the reactor system, letting it melt its way into the ice. Around it, in the heart of the shard, they began to excavate a cavity and sculpt out hoppers: containers designed to hold broken-up ice produced by the mining robots. Twelve augers—long, spiraling ice movers, like the ones used to transport grain into elevators—were set up to convey that loose ice from the hoppers into the space surrounding the warm reactor vessel, where it would melt and be pumped into the core itself. Meanwhile, a separate corps of robots worked on the outside of the shard, melting the ice a little bit at a time, mixing it with the fibrous material they’d brought with them, and letting it refreeze into the much tougher material known as pykrete.
The “steampunk” propulsion system had basically worked as planned—though not without a lot of tinkering and head scratching—on the first “burn” that had put it on the course back to L1. There had, however, been some problems with the augers that were used to feed ice into the reactor chamber. The augers received their inputs of ice from hoppers that had to be filled up by “mining” solid ice from the inside of the shard, a process for which robots were well suited, and so nothing worked at all without the assistance of a small army of robots conveying flakes of ice from mine head to hopper like ants dismantling a
loaf of sugar. This part of it had actually worked. But some of the pieces of ice being mined by the robots had little rocks in them. These jammed the augers. Jams could often be repaired by operating the auger in reverse for a short time, but sometimes a robot, or even a person in a space suit, had to be sent to pry a rock out of the mechanism. An auger accident had led to the death of one member of the crew.
During the months between that first burn and their arrival at L1, Larz did some programming work on the robots, trying to teach them not to collect rocky ice. They conducted a number of system tests intended to make sure that the problems they’d experienced the first time around wouldn’t be repeated during the critical second burn. These ranged from small-scale tests on individual robots all the way up to full dress rehearsals where the entire system would be energized and the reactor turned on to generate thrust for a few minutes.
It had been during the first of those dress rehearsals when something had gone wrong in the core, resulting in damage to the jacket of a fuel rod.
Jiro had an idea as to what had gone wrong. Ymir’s reactor used water—the melted ice of the comet core—as its moderator. In nuclear engineering, that meant a medium that slowed down the neutrons hurled out by fission reactions, making them more likely to stick around long enough to trigger more such reactions. In the absence of an effective moderator, the neutrons would mostly escape from the system without doing anything useful.
Between being as dead as a doornail and running out of control was a narrow band of normal and healthy power output in which basically all commercial reactor operations happened. The essential problem with Ymir’s reactor was that its moderator—being a naturally occurring substance—was impure and unpredictable. The water that flooded into the chamber for the first dress rehearsal had been melted from ice a few months earlier, around the time of the initial “burn,” and had been sitting in the plumbing system ever since then. There, it had been in contact with rocks and grit that had made it through the augers. It had leached various minerals out of that rock, and become something other than pure water. When the reactor was started and the pumps turned on, that impure water was drawn through screens and filters intended to exclude all the debris. But it was nonetheless impure water, and when introduced to the core, it failed to perform its function as a moderator. The reactor was sluggish to get going. With the advantage of hindsight, it could be seen that its neutron economy was suppressed, poisoned by the impurities in the water. Overreacting to the slow start, the operators had pulled the control blades out farther than they would have otherwise. But once the first rush of impure water had been flushed through the system and blown out the nozzle, it had been replaced by relatively pure water, only just now melted from the ice. The reactor’s power had surged, producing a sudden buildup of fission products inside the fuel rods. Some of those would have been gases such as krypton and argon. The gases would have created pressure. Fuel rods were engineered to withstand it, but one of them had failed and ruptured. Possibly it had left the factory in excellent condition but been damaged en route by a nanometeoroid that had left a microscopic flaw. In any case, for whatever reason, the rod burst open and began to spill out the highly radioactive “daughters” of nuclear fission, which had become mixed with the steam being blasted out the rocket’s nozzle.