Dinah related the story. Doob looked distracted at first, perhaps because of all the ham radio jargon, but focused when she showed him the MAC addresses.
“The simplest explanation,” he pointed out, “is that it’s a troll, just messing with you.”
“But how would a troll know those MAC addresses? We don’t give those out—we don’t want our robots getting hacked from the ground.”
“The PR people have come through here, haven’t they? Taking pictures of you and your robot lab. Mightn’t it be the case that a picture got snapped when you had that box open, and some of those PC boards visible?”
“There’s no gravity in here, Doob. I can’t leave things lying around on my desk.”
“Because,” Doob said, “obviously what’s going on here is that someone wants to talk to you through a private channel—”
“And they are proving their identity by mentioning numbers that could be known only to a few people. I get it.”
“And all I’m saying is that a really sophisticated troll would look for some detail like that, in the background of a NASA publicity photo, as a way to fool you.”
“Noted,” Dinah said. “But I doubt it.”
“Who do you think it is, then?”
“Sean Probst,” Dinah said. “I think it’s the Ymir expedition.”
Doob got a distracted look. “Man, I haven’t thought about those guys in ages.”
IT WAS STRANGE THAT A STORY AS EPIC AND AS DRAMATIC AS THE voyage of Ymir could go forgotten, but those were the times they lived in.
The ship had stopped communicating and then disappeared against the backdrop of the sun about a month after its departure from low Earth orbit (LEO) around Day 126. A few sightings on optical telescopes had confirmed that it had transitioned into a heliocentric orbit, which might have happened accidentally or as the planned result of a controlled burn. Assuming it was following its original plan, Ymir should then have made almost two full loops around the sun. Since its orbit was well inside of Earth’s—the perihelion was halfway between the orbits of Venus and Mercury—it would have done this in just a little more than a year, grazing the orbit of Greg’s Skeleton—Comet Grigg-Skjellerup—a couple of hundred days ago. But this would have occurred when it was on the far side of the sun from the Earth, making it difficult to observe. The next event would have been a small matter of impregnating the comet’s core, or a piece of it, with an exposed nuclear reactor on the end of a stick, and then turning it on to generate thrust by blowing a plume of steam out the entry hole. They would have done a large “burn”—pulling out the reactor’s control blades, powering it up, and releasing a plume of steam—that would have altered the comet’s trajectory by about one kilometer per second, enough to put it on a collision course with Earth, or at least with L1, a couple of hundred days later. The timing was awkward, and many had griped about it, wondering why Sean hadn’t gone after some other comet, or plotted some other course that might have brought it home a little sooner. But people who knew their way around the solar system understood that it was near-miraculous good fortune for any comet core to be in a position to be grappled and moved in such a short span of time. The hasty shake-and-bake nature of the Ymir expedition, which had stirred up so much controversy, had been forced by the implacable timeline of celestial mechanics. Time, tide, and comets waited for no man. And even if it had been possible to bring a comet back sooner, it would have been reckless, and politically impossible. What if the calculations were wrong and the comet slammed into the Earth? So, the plan of the Ymir expedition was the only one that could have worked.
If, indeed, it were working at all. And since much of the action—the rendezvous with the comet and the “burn” of the nuke-powered, steam-fueled engine—had occurred while it was on the far side of the sun, this had been very much in doubt until a couple of months ago, when astronomical observations had proved conclusively that Comet Grigg-Skjellerup had changed its course—something that could only have happened as the result of human intervention. The comet was headed right for them. It would have triggered mass panic on Earth had Earth not already been doomed. Since then they had watched its orbit converging slowly with that of Earth, and plotted the time when it would disappear against the sun once more as it reached L1. The reactor would then have to be powered up again, as a huge “burn” would be needed to synchronize Ymir’s orbit with Earth’s and pilot it through L1 to a long ellipse that would bring it their way.
“I THINK ABOUT THEM EVERY DAY,” DINAH ANSWERED.
“When are they supposed to hit L1?”
“Any time . . . but it’s going to be a long burn, they might sort of grease it in over a period of a few days rather than trying to do one sharp impulse.”