“This thing”—he indicated the fat white layer in the middle of the sandwich, like the marshmallow in a s’more—“is probably polyethylene or paraffin, which would be good at absorbing neutrons. Gamma rays might be produced in the process, and so this base plate”—he pointed to the dark graham cracker at the bottom—“is probably lead.”
Dinah already knew what it was, because Sean had told her: the core of a large nuclear power plant, rated at a thermal output of four gigawatts, somewhat hastily reengineered for this purpose. But she had been sworn to secrecy, and so all she could do was let Konrad piece it together himself. “Well,” she said, “those are impressive precautions on what is probably a suicide mission anyway.”
“They want to be alive and capable of doing something when and if they get where they are going,” Konrad said.
“Do you suppose anyone has taken pictures like this from Earth?” Dinah asked. “Because I haven’t seen anything in the media.”
“It was concealed by a fairing until they made their transfer burn,” Konrad said. “I took this a couple of hours ago, when I had my one and only clear shot.”
They had timed that burn so that they would cross the former moon’s orbit at a time when most of the debris cloud was on the opposite side of the Earth, thus minimizing the chance of colliding with a rock.
Nevertheless, a few days after they had passed that distance, and become the longest-range travelers in human history, they stopped communicating.
Until then Ymir had been using powerful X-band radios to communicate over the Deep Space Network—a complex of dishes in Spain, Australia, and California that had been used for decades to talk to long-range space probes. Now she had gone silent. She was still out there—Konrad could still pick her up as a white dot on his optical telescope. Since she was merely coasting for thirty-seven days, not firing her engines, there was no way to tell whether the crew was still alive. A perfectly shipshape Ymir and a crumpled wad of space junk would have looked and behaved the same.
They drew some hope from the fact that nothing came back from her. Ymir had automatic systems that were supposed to phone home without human intervention. If those had continued to function while communication from humans had ceased, it would suggest that the crew were all dead or incapacitated. But the fact that all human and robotic signals had been cut off at the same time suggested that it was a radio problem—perhaps damage to the X-band antenna, or to the transmitter itself.
Ymir became tricky, then impossible to see as she approached L1, since that put her squarely between Earth and the sun. She was assumed to have reached that point on Day 126, whereupon she was scheduled to make another burn that would put her into a heliocentric orbit: an ellipse that would intersect with “Greg’s Skeleton” over a year later—sometime around A+1.175, or a year and 175 days post-Zero. Once Ymir disappeared, from their point of view, into the fires of the sun, there was nothing they could do except wait for her to reach a place where she was observable. If Ymir had suffered a catastrophic failure and been turned into a floating piece of space junk, she would probably cycle back on the return leg of the same orbit and pass close to the Earth again—though L1 was such an unstable place from an orbital dynamics standpoint that she could just as easily wander off into a heliocentric orbit, especially if she’d taken a big hit from a rock that had knocked her off course.
As the calendar progressed through the 130s and to Day 140—two weeks after Ymir ought to have passed through L1—and she did not appear on that return leg, it became clear that she must have transferred to a heliocentric orbit, whether by accident or because of a controlled burn. Assuming the latter, Sean and the other half-dozen members of the crew would have nothing to do for the next year but float around in zero gee and wait. There was nothing that could be done to speed up the journey; it was a matter of getting two orbits to graze each other.
These events, which would have seemed of world-historical significance a few months ago, now seemed like below-the-fold news compared to all that was happening in what had formerly been the sublunary realm.