Текст книги "Seveneves"

Автор книги: Neal Stephenson

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Текущая страница: 23 (всего у книги 57 страниц) [доступный отрывок для чтения: 24 страниц]

Ymir

“. . . AND THEN THE FORCE OF THE VACUUM CAUGHT HOLD OF THE hatch, and to my horror I saw it slam shut right in front of me! I tried to pull it back open, but the suction was too strong. I cannot tell you, Markus, how helpless and guilty I felt when I realized that Dinah was trapped on the other side.”

Markus’s eyes went to Ivy. He had been listening to Julia for a long time, and needed a break.

Ivy threw her hands up. “I was trying to fly this ungainly contraption. I didn’t really understand what was happening even when Julia tried to explain it to me.”

“Yes,” Markus said, “I can’t believe you were able to fly that thing at all. People will be talking about it a hundred years from now.”

Assuming people still exist, Dinah thought.

Ivy was just regarding Markus, blinking slowly, looking for signs that he was being sarcastic. He wasn’t. The Markus bluntness worked both ways: he could blurt out astonishingly generous compliments as easily as he could cut and burn you with his words.

“It sure used up all of my brain,” Ivy said.

They were sitting around the conference table in the Tank. Markus had not used the term “inquest” to describe this meeting, but that was clearly what it was. Or as close as they would ever get, in any case, to a formal determination of what had happened yesterday. It had gotten off to a reasonably brisk start with a summary from Markus, then gone off the rails as Julia had insisted on telling her story “from the beginning”—which turned out to mean from the moment she had woken up in the White House next to her late husband and gone down to breakfast with her late daughter, straight through to the end of the world, and her hastily arranged launch into orbit, some thirty-six hours later. Along the way had been a sequence of mishaps and coincidences just shaggy enough to be somewhat plausible. No liar could fabricate such a story. The narration had lasted for the better part of an hour despite Markus’s increasingly frequent and obvious glances at his Swiss watch, and left all the others in a strange combination of spellbound, bored, horrified, and bemused.

She seemed to believe that they would actually care about all of her interactions with those dead people on that dead planet. It was a common enough mistake among new arrivals. In her case it was magnified considerably by the fact that she was used to being the president. Everyone was always happy to sit and listen to the most powerful person in the world.

“Thank God,” Julia said, “that we were able to—”

“Yes,” Markus said, cutting her off. Plainly he did not wish to hear any more from Julia. But just as plainly he was a little reluctant to move on to the next part of the story.

Everyone seemed to be pointedly not looking at Moira.

“Thank you, Julia,” Markus said, in a tone that made it clear she was free to leave now.

Julia looked a bit startled. “But we haven’t heard from Dr. Crewe yet.”

“But we have heard from you,” Markus pointed out.

The point sank in. Julia didn’t like it. “Very well,” she said, standing up carefully. “As I mentioned before, Markus, I am eager to make myself useful in any way that I can.”

“It is so noted,” Markus said. He looked across the table, deadpan, at Ivy. Dinah knew what they were both thinking: You are worse than useless here—which is why you were never invited. “Thank you, Julia.”

The ex-president turned away from the table. She stopped before the door leading into the Farm and turned back toward Markus one last time with a sad-puppy look on her face, perhaps expecting him to just slap his thigh and laugh at the joke and warmly invite her back to her seat. When this failed to happen, a transformation came over her face that Dinah found mildly frightening to watch.

What would it be like, she wondered, to be nuking people one day, and, less than a week later, to be asked to leave a meeting? Evidently it did not put Julia in the best of moods. J.B.F. turned her back on them, as much to hide her face as to find the way out, and opened the door. During the few moments it was open, Dinah caught sight of a young woman in an Islamic-style face veil standing just outside of it, waiting. The bottom half of her face was covered, but her eyes brightened and her body language was warm as she saw Julia emerging. Julia reached out to her affectionately and laid a hand on the small of her back as she turned. The two of them walked away shoulder to shoulder as the door closed.

Remaining in the Tank were Markus, Dinah, Ivy, Moira, Salvatore Guodian, and Zhong Hu, an applied mathematician who was their head theorist when it came to swarm dynamics. Others knew more about orbital mechanics and rocket engines—the old-school techniques for managing individual space vehicles’ trajectories—but Hu, a specialist in complex systems, was the main architect of Parambulator, and the only person who could quite understand and explain what went wrong, or right, in a swarm. He’d spent most of his life in Beijing, but with enough time in Western universities to get along fine in English. In response to a nod from Markus, he said, “I have evaluated what happened. As we already know, there was a cornering event leading to a bump.” This being the polite term for a mild collision between arklets. “But still, Arklet 214 had enough control authority that it could have avoided the second event.”

“Then why didn’t it?” Markus asked.

“The algorithm predicted a near miss and so it took no action beyond routine attitude corrections. The human operator was distracted and disoriented and so was reluctant to correct course manually.”

“I can’t fault the human,” Markus said, “since we have warned them so many times about the consequences of flying by hand. But what went wrong with the algorithm?”

“Nothing went wrong with it,” Hu said. “It had bad data. I will show you.” With a few taps on his tablet he brought up a three-dimensional model of Izzy on the big screen above the conference table. To a first approximation, this seemed reasonably up to date; it depicted modules and space vehicles that had been added to the complex only within the last couple of days. “This is the model that the system was using yesterday for collision avoidance.”

Dragging his finger around on his tablet, he rotated the model on the screen so that they were looking at the nadir side. He zoomed in on the distinctive “handlebar” shape of the Human Genetic Archive: the pair of cold storage units projecting to port and starboard below the Zvezda module. The view was much the same as what Dinah had seen from the Flivver the day before.

“Hang on, is this the exact model? Is this everything?” Ivy asked.

“Yes,” Hu said.

“This doesn’t include the thermal protection,” she pointed out. “That adds at least a meter to the collision envelope.”

“That is correct,” Hu said. “In that sense, this model is obsolete. We have replaced it now with an upgraded version.”

As all understood, this was no one’s fault. The Arkitects had been struggling for almost two years to keep their three-dimensional model of Izzy up to date and accurate: a nearly impossible task when it changed every day. Soft goods like thermal protection blankets tended to get a lower priority. Humans, looking at the model, would mentally add those. Computers weren’t that smart.

“Still,” Markus said, “we take the model with a grain of salt. No arklet should ever pass that close.”

“Let me show you what happened,” Hu said, and brought up a video, shot from an external camera apparently mounted on one of the trusses.

The Human Genetic Archive and its surrounding blanket of thermal protection were not centered in the frame—they were down in the lower right corner. So the camera angle wasn’t ideal. But they could see what happened. The arklet approached, creeping in gradually from the port side with closing velocity no greater than a slow walk.

“Is this real time?” Sal asked.

“Yes. Because it was an extremely low-speed approach it was not viewed as terribly dangerous.”

“It looks like it’s going to be a near miss,” Sal said.

“It was—until this,” Hu said, and freeze-framed the video. It wasn’t easy to make out, but they could see a tiny flash on the forward halo of Arklet 214. “The thruster fires—a small course correction under automatic control.” He stepped it forward. The flash faded but expanded into a dim gray cloud. “Exhaust gases. Expanding rapidly but moving quite fast.” He stepped it forward several more frames until they could see the thermal protection blanket recoiling from the impact of the gas. A seam parted between two adjoining blankets and one of them flailed out like a rag caught in a wind gust.

Hu let the video run now, and they saw the arklet’s rear halo snag on the loose blanket and rip it away, exposing the Human Genetic Archive to the orange radiance of Earth’s atmosphere.

Ivy said, “If that thruster hadn’t fired at the wrong moment—”

Hu nodded. “Arklet 214 would have passed underneath with two meters to spare. Not a margin to be proud of. But it would have been enough.”

After a pause, Hu added, “The HGA’s thermal protection system could have been designed better.”

Another pause in which everyone else waited to see who would be the first to laugh. If it weren’t for dark humor, they’d have no humor at all.

Hu seemed to sense it. “What I mean is that it was engineered for normal thermal loads.”

“Meaning sunshine,” Dinah said.

“Yes. Not for radiant heat shining up from the atmosphere below it.”

“The same thing is true of many parts of Izzy, of course,” Markus said. “We are having thermal overloads all over the place now. Moira, what’s the damage?”

Dinah had to give Markus credit for a kind of finesse for the offhanded way he dropped the question in. Moira, who had been quiet through the whole meeting, took a moment to snap out of her reverie.

“Well,” she finally said, “as Hu said, the thermal protection system—”

“Was bad,” Markus said. “We know.”

“There was no backup system.”

Markus said, “Of course not. The cooling system for the HGA was the rest of the universe. We do not expect to have a backup system for the rest of the universe. We can rely upon it to be cold most of the time.”

“Because of the accelerated schedule, caused by the Eight Ball—”

“Stop,” Dinah said.

Everyone looked at her.

“Let’s get this over with,” she said. “Look. When I was fourteen, one of my dad’s mines collapsed and killed eleven employees. It was terrible. He never really got better. Of course, he wanted to know what had happened. It turned out to be a long story. One thing led to another, which led to another . . . the individual steps all made sense, but no one could have seen the whole thing coming. Of course, he still felt responsible, but he wasn’t, in any normal sense of that word.

“So here’s what happened,” Dinah went on. “Sean Probst started an asteroid mining company that sent up a bunch of cubesats and gathered a lot of data about near-Earth asteroids, which he kept secret. He took the database with him on his mission to Greg’s Skeleton. His radio got hit by a rock and destroyed, so he couldn’t communicate. At the last minute, when it was basically too late, he had the idea to look at the database. He learned about the Eight Ball. He alerted me, I alerted Doob, Doob alerted everyone else, and we pushed up the schedule for everything. Moira pulled the trigger on the project, which had been planned for over a year, to disperse the HGA samples to the arklets. Like every other project in the history of the universe, it went slowly at first because all kinds of snags came up. And not only that, but all of the Flivvers were spoken for and all of the space suits were busy, because of the Splurge. So not much got moved. It was obviously safer to keep the samples in cold storage in the HGA while all of these logistical problems got sorted out. The Splurge happened and a lot of random shit got launched in our general direction and made Parambulator light up like crazy. Arklets were getting cornered on a pretty regular basis. We almost lost a couple. Ivy and I took off in the Flivver to fetch Julia and probably added a lot of other noise and chaos to that problem. Then, the thing we just watched happened. Arklet 214 tore most of the badly designed thermal protection system off of the HGA and exposed it to the direct radiance of the Earth’s atmosphere. The samples all warmed up before replacement thermal protection could be jury-rigged. All of those samples have been destroyed. Right, Moira?”

Moira, apparently not trusting her ability to speak, nodded.

“Okay,” Dinah said. “So I think that what Markus is really asking is how many of the samples in the HGA actually got moved to safe cold storage in other locations before this happened. In other words, how many survived?”

Moira cleared her throat and said, in a faint voice, “About three percent of them.”

“Okay. I only have one other question,” Markus said. “Have you talked to Doob?”

“I’m sure he suspects,” Moira said, “but I have not officially broken the news to him. I wanted to be absolutely sure first.”

“Are you sure now?”

“Yes.”

Markus nodded and spent a few moments thumbing something into his phone. “I am inviting him to join me and Moira here immediately,” he said.

Everyone who was not Markus or Moira stood up to leave. Markus held up his hand to stay them. “Before you go, let me say something about the Human Genetic Archive that was lost.”

He then paused for effect, until everyone was looking at him.

“It was always bullshit,” he said.

Everyone took a moment to consider it.

“Are you going to tell Doob that?” Ivy asked.

“Of course not,” Markus said, “but the real purpose of the HGA was politics on Old Earth.”

“Is that what we’re calling it now? Old Earth?” Sal asked, fascinated.

“That’s what I am calling it,” Markus said, “in the increasingly rare moments when I actually think about it.”

“Thank you, Markus,” Moira said.

HE HAD KNOWN, OF COURSE. IZZY’S COMPLEXITY WAS SO GREAT AS to belie its tiny size: a few hundred people sorted into a volume the size of a few jetliners. News traveled fast. Everyone had known within a few hours that the Human Genetic Archive had been almost completely destroyed.

He was in the Tank with Markus and Moira. They were gazing across the table at him, patiently awaiting some kind of reaction.

“Look,” he finally said, “Doc Dubois is no more. That was a persona, you understand? Just an act. I’m a private person. I do not spontaneously emote. Especially when people are watching me and expecting it. A year from now, when I’m alone, when I least expect it, I’ll break down in sobs over this. But not now. It’s not that I don’t feel. But my feelings are my own.”

“I am very sorry that it happened,” Moira said.

“Thanks,” Doob said, “but let me say what all of us are thinking. Seven billion people died yesterday. Compared to that, the loss of some genetic samples is nothing. The embryo that Amelia and I created together, and that I brought up here with me . . . well, that was a special favor that J.B.F. granted me as an incentive to come up here. No one else got that kind of special treatment. It was unfair. I knew it. I accepted it anyway. So here we are.”

“Yes,” Markus said. “Here we are. Going forward—”

“But I’m not sure I agree with you,” Doob said, “that the HGA was so insignificant.”

Markus bridled his impatience and raised his eyebrows. Doob looked at Moira. “What was the term you used? Heterozygosity?”

“Yes,” Moira said. “The stated purpose of the HGA was to ensure a sufficiently diverse genetic basis for the human race.”

“Sounds important to me,” Doob said. “What am I missing?”

“We have tens of thousands of human genomes recorded in digital form. From all different parts of the world.”

“So there’s your heterozygosity. That’s what you’re saying,” Doob prompted her. “That’s why”—he glanced at Markus—“the HGA wasn’t really needed.”

“Yes, but there’s a but,” Moira said.

“Okay, what’s the but?”

“The digitized sequences, as I’m sure you’ll understand, are only useful so long as we have the equipment needed to transcribe them into functional chromosomes in viable human cells. By contrast, to make use of a sperm sample, all we need is a turkey baster and some lube. But to make use of a DNA sequence stored on a thumb drive, we need—”

“All of the equipment in your lab,” Doob said.

Moira looked a bit impatient. “What you are referring to as my lab bears the same relationship to a proper lab as some ones and zeroes on a thumb drive does to a living human. It is a collection of crated equipment that cannot even be unpacked and used in zero gravity. And even if we set it all up and turned it all on, it would be useless without a staff of Ph.D.-level molecular biologists.”

“Really? Useless?” Markus asked.

Moira sighed. “For small-scale work, one sample at a time, well, that is easier. But to reconstruct a genetically diverse human population—”

“But, Moira,” Markus said, “we cannot do that anyway until so many other things are in place. A large population cannot live in arklets eating algae. We need to establish a viable and safe colony first. Then, we build your lab. Then, we create a more diverse ecosystem: better food, greater stability. Only then do we even begin to worry about the heterozygosity of the human population. Until that time, we have more than enough people to create healthy non-inbred children just by the usual process of fucking each other.”

“That is all true,” Moira said.

“And that is the basis of my statement that the HGA was bullshit,” Markus concluded.

“You’re saying,” Doob said, “that if we had all of the prerequisites in place—the colony, the ecosystem, the talent—needed to actually exploit the HGA—”

“—we would no longer need it, yes, this is my point!” Markus said. “Can we please stop wasting time on it now?”

“How would you prefer to be spending time, Markus?” Moira asked, giving Markus an amused, owlish look through her glasses.

“Talking about how to get there. How to realize that situation we were just talking of.”

“And how might I contribute to that, given that the HGA is ninety-seven percent destroyed and none of my equipment will be usable for a long time?”

“I want to talk of preserving that equipment,” Markus said, “preserving it against all hazards, and then getting it to a safe situation where we can one day construct this laboratory you speak of.”

“It’s about as safe as we can make it, isn’t that so?” Moira asked. “It was given a sort of privileged position off of Node X—quite close to Amalthea. It’s not living dangerously, the way we are at the moment.”

She was referring to the notion, frequently discussed by Arkitects, of the Cone of Protection that supposedly existed in the lee of Amalthea. To the extent that the paths of incoming bolides were predictable, Amalthea could be pointed into them and used as a sort of battering ram. The forward surface of the asteroid would take a beating—but a solid slug of ancient nickel and iron could survive quite a lot. Anything situated up against its aft surface would be sheltered against virtually all hazards. But the protected zone did not, of course, stretch back infinitely far. The farther you lagged behind Amalthea, the more likely you were to get hit by a bolide coming in from an off angle. The Mining Colony was in the safest position, since, by its nature, it had to be right up against the asteroid. Almost as safe was the cluster of modules connected to Node X, immediately aft of the SCRUM, which was where all of Moira’s gear had been stashed. Behind that, the protected zone narrowed, a long acute cone, finally disappearing altogether somewhere aft of the Caboose. When Moira joked about “living dangerously” she referred to the fact that T3, the third torus, in which they were sitting now, was rather wide and rather far aft, placing it close to the limits of that cone. Efforts had been made to beef up its shielding, but it was still at higher risk than many other parts of Izzy.

Markus nodded. “Your stuff is pretty safe. But it would be safer if we moved it inside of Amalthea. I have talked to Dinah about it. She says that they could mine out cavities and store things of great importance there.”

A silence while Doob and Moira pondered it.

On one level, Markus’s proposal was perfectly obvious. Of course anything would be safer inside of a huge metal asteroid.

On another level, it had ramifications.

As of a few days ago—pre–White Sky, the last time anyone had been able to think straight—the fate of Amalthea and the Mining Colony had still been subject to debate. Was the asteroid the boulder in the wheelbarrow that had to be dumped? Or was it the aegis that would shelter the entire human race? The argument had come down to statistics. They just didn’t have enough data to make a decision.

By suggesting that Moira’s equipment be moved into the interior of Amalthea, Markus seemed to be committing to a specific course of action.

It was a course that Doob instinctively agreed with. But it was a bit strange for a man like Markus to just decide on a course of action before the numbers were in.

Or did he know something Doob didn’t?

Moira, in any case, went first. “What if we Dump and Run?”

She was referring to a gambit, frequently discussed and war-gamed, in which Amalthea would be cut loose and abandoned, and Izzy, lightweight but unprotected, would boost herself to a higher orbit with fewer bolides flying around in it.

“Then we would simply have to move all of that stuff back to Node X first,” Markus said. “Or wherever we felt was safest.”

This elicited a searching look from Moira. Markus held up his hands. “But I take your point. I am increasingly biased against Dump and Run.”

“You know how I feel about the Swarmamentalists,” Moira said.

She was referring to another of the basic gambits, Pure Swarm, in which everything—presumably including Moira’s lab—would be distributed among arklets, which would then collectively move to higher orbit. People and goods would move among them through a decentralized market-based economy.

“Listen,” Markus said, “now that everyone below is dead, and we don’t have to put up so much with bullshit, you will find that Hu and the others have a more nuanced view than they were letting on before.” He referred to the fact that Zhong Hu, as the foremost swarm theorist and the brains behind Parambulator, was assumed to be a Swarmamentalist.

Doob nodded. It still took some effort to remind himself that the millions of Internet commentators arguing for this or that strategy were all ghosts now.

“You know something,” Doob blurted out. Then, as the thought was coming into his head, he added, “From Dinah. The radio.”

“Yes,” Markus said. “Ymir is coming in hot, high, and heavy.” He surrounded those three words with air quotes.

“What does that mean?” Moira asked. “She’s made of ice, how can she be hot?”

“She is approaching with a high closing velocity. Not unmanageable. But . . . somewhat exciting.”

“And ‘high’?” Doob prompted him.

“Sean also transmitted his params,” Markus said. “It would seem that he did us a large favor. He executed the plane change while it was still easy to do so, way out around L1.”

“So when he says he’s coming in high,” Doob said, “he means that Ymir has a high orbital inclination—close to ours?”

“Very close to ours,” Markus confirmed. “He is dropping this big chunk of ice into our lap.”

“So,” Moira said, “on top of everything else, Sean Probst is now preparing to dive-bomb us with a comet?”

“A piece of one.”

“A big piece,” Doob guessed, “if he specified ‘heavy.’”

“The number was impressive.” As Markus said this, he shifted toward Doob and looked him in the eye.

“Oh wow,” Doob said. “Is it enough for the Big Ride?”

“If we can get Ymir to rendezvous with Izzy, then yes,” Markus said. “It is more than enough.”

The Big Ride was the third of the basic options. It meant to boost Izzy in its entirety—Amalthea and all—to a much higher orbit. It had been considered implausible because of the amount of propellant that would be needed. Not just implausible but—absent the timely return of Ymir—physically impossible. Despairing of Sean’s chances, its supporters had lately tended to suggest scaled-down variants, such as reshaping a small percentage of Amalthea into bolide deflectors and ditching most of its mass.

“Including the plane change?” Doob asked.

A trace of a smile came onto Markus’s face. He knew exactly what Doob was thinking. For, unable to get Cleft out of his head, Doob had shown pictures of his favorite piece of the moon to Markus, to Konrad, to Ulrika and Ivy and some of the others who seemed to make up the informal power structure of the Cloud Ark.

“Let me be clear,” Markus said. “When I speak of the Big Ride, I mean it for real. We take all of Amalthea with us. We raise the orbit to the moon’s. We change the plane. We circularize. And we end up safe and sound in Cleft.”

“And Ymir carries enough water for that mission?”

“Yes,” Markus said, “if we can control her and bring her in.”

“Isn’t that Sean Probst’s job?” Moira asked.

“Not anymore,” Markus said. “The information I just imparted to you was in Sean’s final transmission.”

Moira and Doob looked at him sharply.

“The health situation has been not so good, for a long time,” Markus explained. “Sean was the last member of the expedition to die.”

“Are you saying that Ymir is a ghost ship?!” Doob asked.

“Yes.”

“And there’s no way to remote-control her,” Moira guessed.

“Unfortunately Dinah’s Morse code cannot help us in that regard,” Markus agreed.

“So someone has to go and—”

“Someone has to go and land on that fucking big piece of ice,” Markus said, “and get inside of Ymir and restart the nuclear reactor and commit the final burns that will bring her into sync with Izzy.”

“Who the hell—” Doob began, but Markus cut him off by pointing to himself. He did this in a somewhat awkward fashion that, deliberately or not, looked like a pantomime of suicide by handgun. He said, “I am placing Ivy in command of Izzy and the Cloud Ark tomorrow. I am assembling a crew that will depart in a MIV and make a rendezvous with Ymir. We will board her and manually execute the procedures needed to bring her under control and get her payload to Izzy. We will then use what is left of the ice to raise Izzy’s orbit—and we will bring Amalthea with us on the Big Ride.”

“That’s . . . major,” Moira said. “Who knows? When were you going to announce it?”

“I just decided it now.” Markus sighed. “Listen, it is the only way. In my heart I always considered Dump and Run and Pure Swarm both to be too risky. What happened with the HGA just makes this more obvious. The only wise course is the Big Ride. It will take a long time—two years or something. But during all that time the most important resources can be sheltered within Amalthea. And by that I mean you and your equipment, Moira. You can have whatever resources you need from the Mining Colony to create a safe location for the genetics lab.”

“Okay,” Moira said, “I’ll talk to Dinah.”

“Talk to whomever she delegates,” Markus said. “Dinah is going to have to come with me on the expedition. I need her to deal with all of those verdammt robots.”

“How can I help?” Doob asked. He wondered if Markus might dragoon him as well, and was torn between being afraid of that and tremendously excited.

“Figure out how we are going to do it,” Markus said, after considering it for a few moments. “Lay in a course for Cleft.”

“Yes,” Doob said. “I’ll do that.” The little boy in him was crestfallen that he wasn’t going on the adventure. Then he reminded himself that he was already part of the biggest adventure ever, and that, so far, it had been altogether miserable.

ALL CONVERSATIONS WORTH HAVING ABOUT SPACE VOYAGES WERE couched in terms of “delta vee,” meaning the increase or decrease in velocity that had to be imparted to a vehicle en route. For, in a common bit of mathematical shorthand, the Greek letter delta (Δ) was used to mean “the amount of change in . . .” and V was the obvious abbreviation for velocity. The words “delta vee,” then, were what you heard when engineers read those symbols aloud.

Since velocity was measured in meters per second, so was delta vee. The delta vees bandied about in spaceflight discussions tended to be large by the standards of what Markus was now calling Old Earth. The speed of sound, for example—a.k.a. Mach 1—was three hundred and some meters per second, and most earthbound people would consider it awfully damned fast. But it hardly rose to the notice of most people who talked about space missions.

A common delta vee benchmark had been the amount needed to get something from an Old Earth launch pad to an orbit like Izzy’s. This was some 7,660 meters per second, or more than twenty-two times the speed of sound: an impossible figure for any object that had to fight its way through an atmosphere. Once a vehicle had reached the vacuum of space, though, things became simpler: rocket engines worked more efficiently, drag and aerodynamic buffeting were absent, and the consequences of failure weren’t invariably catastrophic. Getting it from point A to point B was a matter of hitting it with the right delta vee at the right time.

Sean Probst’s delta vee history, from his departure from Earth until his departure from life, had gone something like this. The launch from terra firma to Izzy on Day 68 had required a delta vee of 7,660 m/s according to a naive calculation; but as any old space hand would know, losses due to atmospheric friction and the need to push back against gravity would have elevated the practical number to more like 8,500 or 9,000.

Once he had collected Larz and most of Dinah’s robots, Sean had needed to execute a plane-change maneuver to get from the Izzy orbit—which was angled at about fifty-six degrees to the equator—to the equatorial orbit in which Ymir was being assembled. This was one of those circumstances in which human intuition got it all wrong. The Izzy orbit and the Ymir orbit did not seem all that different in most respects. Both of them were a few hundred kilometers above the atmosphere. Both were essentially circular (as opposed to elliptical). And both went in the same direction around the Earth. The only real difference between them was that they were at different angles. And yet the delta vee required to get from one to the other was large enough that it had been necessary to launch a separate rocket, carrying nothing but extra propellant, just to refuel Sean’s vehicle in preparation for the plane-change burn.