Having settled that in her mind, she focused her attention back on what Sean was saying.
“Cloud Ark as distributed swarm: fine. I get it. Sign me up. Much safer than putting all our eggs in one basket. What makes it safer? The arklets can maneuver out of the way of incoming rocks. Other advantages? They can pair up to make a bolo, and spin around each other to make simulated gravity. Keeps people healthier and happier. How do they do this? By flying toward each other and grappling their tethers together. What happens when they want to break up the bolo, and go solo? They decouple the tethers and go flying off in opposite directions, unless they use their engines to kill that centripetal motion. What do all of these activities have in common?”
They’d gotten used to Sean’s habit of asking, then answering his own questions, so were caught off guard now that he actually seemed to be expecting an answer.
Dinah and Ivy had been joined by Konrad Barth, the astronomer; Larz Hoedemaeker; and Zeke Petersen. The latter finally rose to the bait.
“Use of the thrusters,” he said.
Sean nodded. “And what happens when we are using the thrusters?”
Dinah had an advantage, since she already knew that Sean was concerned about mass balance. “We’re dumping mass. In the form of used propellant.”
“We’re dumping mass,” Sean said, nodding. “As soon as the Cloud Ark runs out of propellant, it loses the ability to do all of the things that make it a viable architecture for long-term survival. It becomes a big sitting duck.”
He let them roll that around in their heads for a bit, then went on: “Mind you, almost everything else that we do up here can be done with minimal effect on mass balance. We can recycle our urine to make drinking water and our poo to make fertilizer. Very few of our activities involve just releasing mass into space in a way that we can’t get it back. This is the exception. I have been ranting and raving about this ever since the idea of the Cloud Ark was announced. So far all I get in return, from the powers that be, are vague answers and hand-wavy happy talk.”
Ivy and Dinah looked at each other in a way that foretold a one-on-one, after-meeting tequila session.
So, Dinah thought, Ivy had been wondering about this too, in the back of her mind. Worrying about it. Trying to read the tea leaves during those teleconferences down to the ground.
It was something to do with Pete Starling, she now saw. Which meant that it was somehow related to J.B.F.
Zeke was one of those open-faced, basically optimistic team players one saw frequently in the junior officer ranks of the military. “This is so obvious, in a way,” he pointed out. “They have to have thought of this.” Which was Zeke’s way of saying I’m sure that this is all being handled by people above our pay grade.
“You would think,” Sean said, nodding.
Konrad shifted in his chair uneasily and thrust his bearded face into his hand. Unlike Zeke, he was not the sort to place the sunniest interpretation on the problem.
“If the world were run by scientists, engineers,” Sean said, “then this would be a no-brainer. We have to go get more mass. Stockpile it so we don’t run out.”
“It’s got to be water. You’re talking about a comet core,” Dinah said.
“It’s got to be water,” Sean agreed. “You can’t make rocket fuel out of nickel. But with water we can make hydrogen peroxide—a fine thruster propellant—or we can split it into hydrogen and oxygen to run big engines.”
“I’m waiting for the other shoe to drop in what you just said,” Ivy muttered. Then she spoke up more clearly: “But the world isn’t run by scientists and engineers—is that where you’re going with this?”
Sean turned his hands palm up and shrugged theatrically. “I’m not a people person. People keep telling me this. Some who are people persons might be focusing on that angle.”
“The people angle,” Konrad said, just clarifying.
“Yeah. The seven billion people angle. Seven billion who need to be kept happy, and docile, until the end. How do you do that? What’s the best way to calm down a scared kid, get them to go back to sleep? Tell them a story. Some shit about Jesus or whatever.”
Zeke winced. Konrad rolled his eyes, then glanced at the ceiling and pretended he hadn’t heard this.
The idea Sean was playing with here was so monstrous in a way that it was almost inconceivable: that everything they were doing up here was a lullaby for the seven billion down below. That it could not actually work. That they were just putting on a show of getting ready. That the people of the Cloud Ark would live only a few weeks longer than the ones left behind.
As such, Ivy and Dinah and Konrad and Zeke ought to have been freaking out at this point.
But none of them—not even Zeke—reacted very much.