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.