Doob had brought with him a small can of compressed air—a common convenience used by electronics technicians to blow dust away from things they were working on. He aimed it “down” toward the aft end of the arklet and pressed the button. Air hissed out and he began drifting “up” toward the front door. He raised a hand above his head in time to kill his upward motion against the forward bulkhead, then turned to look into a different camera.

Good. It was the third time he’d attempted this, and he was running out of canned air.

“I can’t drift far, confined as I am to the pressure hull. But you can imagine that if I hadn’t been able to stop—if I’d been out on a space walk—I might have drifted a long way. And what the science of orbital mechanics tells us is that no two objects in orbit can have the same six numbers, except in the special case I just showed you, where I was inside the hollow arklet so that both of our centers of gravity could coincide. An arklet, or any other object, that is off to the port side of Izzy, or to starboard, or to the zenith or nadir side of it, or forward or aft of it, has different numbers by definition. It’s in a different orbit. And so it is going to drift.”

He mentally reviewed his notes. Here he had intended to be more specific about the nature of that drift. If it’s in a higher orbit, it’ll fall behind. If it’s in a lower orbit, it’ll race ahead. If it’s off to one side or the other, it’ll converge, then diverge, on a ninety-three-minute cycle. Only if it’s directly forward, or directly aft, will it maintain the same relative position. But he thought maybe he could link that out to a different video, one with more graphics. Better to get to the point.

“The moral of the story? In space, there is no such thing as formation flying. Physics will cause two nearby objects to drift closer together or farther away. If you want to preserve a formation, such as a swarm, you have only two options. Physically connect the arklets together, so that they become one object, or else use the thrusters to correct for the drift.”

There was another option, which was to put them in single file, like a train in space, but it didn’t seem very swarmlike and so he left it out of the reckoning for now. Minutes after the video was posted, outraged YouTube commentators would be all over him, pointing out the error and attributing it to dishonesty, incompetence, and/or a conspiracy.

His last task was to record a voice-over that would be played over footage of young Arkers training in huge industrial video arcades, thrown together for just that purpose in places like Houston and Baikonur. “It’s not difficult to learn this stuff—any video gamer can pick it up in a few minutes. Just ask these young Arkers, brought together from all over the world, who’ve been honing their arklet piloting skills using precision simulators. Most of the time, of course, the arklets will be flying themselves, on autopilot. But if and when it’s necessary for a human to take the controls, these young people will be ready for it.”

The task complete, he established a link between his tablet and the wireless network of this arklet and spent a few minutes moving video files around so that he could edit them later. Catching sight of himself in freeze-framed thumbnails, he was struck by the roundness of his face—a typical symptom of zero gee as the body retrained itself in how to distribute fluids through its tissues. Up here it was the mark of the newbie. Doob had been in space for six days; this was A+1.0, one year to the day since he had stood in the Athenaeum and watched the moon disintegrate.

Arklet 2, now outmoded by newer models, was docked at the far end of a hamster tube on the port side of the big truss. Sooner or later it would probably be used for overflow storage or sleeping quarters. Doob passed through its docking port and began making his way down the hamster tube. As he’d learned on his way here, this was going to take a while; the tube was barely large enough to accommodate a svelte human in a polyester coverall. A large man in a pressure suit banged and scraped the whole way. And yet it was easier to do it with the suit on than to drag the empty suit behind you, or push it ahead of you, like a zero-gee murderer trying to dispose of a body.

In a few minutes he was able to reach a node, right along Izzy’s central axis, where he had more space to move around, and there he began taking the suit off. This was not a full-fledged space suit, which, with its huge backpack life support system, would have been much too bulky for the hamster tube. It was just a helmeted coverall of the type worn by high-altitude pilots. It had a leak, and so was useful only as a costume. Escaping from it developed into a sort of wrestling match, with a lot of cursing and drifting around, banging into walls.

At an opportune moment, he felt a sharp tug on the rear collar of the suit. This pulled it down to the point where he could shrug out of it and get his arms free. “Thanks,” he said, and then looked over his shoulder to see a familiar face gazing at him quizzically.

“Aren’t you a little short for a storm trooper?”

“Moira?!” Doob said. He grabbed a handle on the wall so that he could spin himself around and get a better look. His glasses had gone askew during the wrestling match, so he poked them back up on his nose. It was her all right, suffering from a clear case of moon face.

He had last seen Dr. Moira Crewe at the Crater Lake announcement, where she had been assisting her mentor, Clarence Crouch, the Nobel Prize–winning geneticist—the poor sod who had been given the job of explaining the Casting of Lots to the world. Since then Clarence had died of cancer in his Cambridge house, surrounded by biological samples and scientific memorabilia that would not long survive the onset of the Hard Rain. No doubt it had been a blessing for him. Doob had lost track of Moira after that, but of all the people on Earth she was one of the most obvious candidates for inclusion on the Cloud Ark. She was of West Indian ancestry, wearing her hair in finger-length dreadlocks that had adapted pretty well to zero gravity—better than white-people hair, for sure. Moon face had added a few years to her apparent age, but Doob knew her to be in her late twenties. Raised in a dodgy part of London, she’d gone to a posh school on scholarship and went on to earn a biology degree at Oxford. She had gone to Harvard for her Ph.D., working with a project there on de-extinction. Her general charisma, and an accent that Americans found charming, had made her into the most well-known spokesperson for that project. She had done TED talks and other public appearances describing her lab’s efforts to bring the woolly mammoth back to life. After a brief sojourn in Siberia, working with a Russian oil billionaire who wanted to create a nature preserve stocked with formerly extinct megafauna, she had returned to the UK and begun postdoctoral work with Clarence.

It was not the first time Doob had been pleasantly surprised to bump into a colleague who had, unbeknownst to him, been sent up to Izzy. It always raised an awkward point of etiquette. It was tempting to express delight and give the person a big hug, as you’d naturally do if you encountered them at a party in Cambridge or on the street in New York City. But none of them had come up here on a happy errand. And Moira anyway had a certain owlish way about her, a way of keeping her distance.

And hugging people in zero gee was harder than it sounded. You had to get to them first.

Doob held his arms out to his sides. “Hug,” he said.

She did the same. “Is that what one does here?” she asked.

“It is not unheard of. Moira, PCA, it is good to see you up here.”

PCA was an abbreviation for “present circumstances aside” and had become a staple of Facebook, Twitter, and the like.