If all had gone perfectly, the nuclear burn would have slowed Ymir down to the point where a rendezvous with Izzy could then have been achieved with a few small additional delta vees. They had hoped this might happen, but not seriously expected it. The best they could really hope for was to shed some velocity and reduce the height of their apogee.
That figure—the distance separating the Earth and the ship at the top of her orbit—was directly related to how much velocity she had at the bottom. Because Ymir had “fallen” in from an extremely high apogee, far beyond the moon’s former orbit, she had come in screaming hot for her skip off the atmosphere. Every bit of velocity that was killed by the huge nuclear retro-rocket burn, or by friction with the air, translated into a lower altitude at the succeeding apogee, which—depending on how the numbers had worked out—would occur weeks, days, or hours later.
The answer, once they had run the numbers, turned out to be hours.
In one sense, Ymir had missed her target by a mile; the total delta vee she had achieved had been less than a third of what they’d hoped for. And yet this had been enough to bring her apogee down from far beyond the moon’s orbit to a figure only about thrice the altitude at which Izzy circled the Earth.
Likewise, the period—the amount of time it took to complete an orbit—had dropped from seventy-five days to a mere eight hours. The lesson being that huge alterations in those figures could be purchased for comparatively small amounts of delta vee.
Bringing Ymir the rest of the way down to Izzy’s orbit, on the other hand, would require twice as much delta vee as they’d wrung out of the “burn” just completed.
Long before worrying about that, however, they would have to survive the next eight hours.
Ymir’s apogee might have been radically altered, but her perigee altitude was unchanged—meaning that it was still dangerously low. If they took no action, the next go-round would therefore bring them roaring and bouncing across the top of the atmosphere again.
On one level, raising the perigee a bit, so that they’d never have to worry about the atmosphere again, was an easy task. They could do it with a small but precisely calibrated burn at apogee. In a normal space mission, such a thing would have been straightforward. Here, it was complicated by two factors. First of all, their success in lowering the apogee, and shortening the period, had imposed a tight deadline—four hours after perigee—when that burn needed to occur.
The second complication was the ship’s slow tumble. This meant that their nuclear rocket engine was never pointed in the right direction, save by lucky accident. During the big burn at perigee, they had wanted the nozzle pointed forward, so that it would serve as a huge retro-rocket. The upcoming burn at apogee was intended to speed her up a bit, and so they needed the nozzle pointed aft. But as long as she tumbled, it was aimed in no particular direction.
So their task now was to stabilize Ymir’s attitude by using her thrusters to push back against the unwanted rotation. And, as they had discovered the first time they’d tried it, her thrusters were small and weak compared to the momentum of the big ice shard. In aerospace lingo, they lacked control authority. Ymir was like a truck skidding on a patch of oil, responding only faintly to the steering wheel. That problem had been alleviated somewhat by the large expenditure of mass during the burn. Many tons of ice had been hurled out the nozzle in the form of steam. Ymir was lighter and more wieldy as a result. Calculating exactly how much more wieldy she was, and what it meant for the thrusters’ control authority, was, in itself, a significant task that consumed another half an hour just for a rough estimate.
The result was not encouraging. In the three hours remaining, there was simply no way that Ymir’s attitude control thrusters—designed for tiny adjustments over long spans of time—could neutralize her tumble. The tumble wasn’t especially fast—the crew in the command module could barely sense that they were rotating—but it was enough to make the next rocket burn impossible. And if they couldn’t make that burn in three hours, they’d scrape the atmosphere again in an additional four, and again eight hours after that. They might survive one more ride like the first one, but they couldn’t survive two.
Once all of this had become clear to Markus, he had divided the crew in half, leaving Dinah and Jiro in the command module’s common room to look after the propulsion system and going “above” with Vyacheslav to consider the problem of attitude control.
Dinah’s task was, comparatively speaking, routine. During the perigee burn, they had expended most of the ice stored in the hoppers. Some of the augers had jammed, and the whole ice-mining operation had been thrown into general disarray as she had improvised solutions to problems that came at her from every direction. Robots were in the wrong places; some hoppers were overfull while others were empty. New ice needed to be mined and old ice needed to be rearranged. Fixing all of that in time for another burn in three hours was not an insuperable task, but it would require her full attention. Likewise, Jiro had a few reactor issues to think about. Both of them would have to toil diligently between now and the apogee burn in order to be ready.
Assuming, that is, that the other half of the crew had, in the meantime, figured out a way to get Ymir aimed in the right direction. Markus had moved that job to another part of the ship where it wouldn’t pose a distraction to the propulsion crew. Or such was his intent; but in moments when Dinah lost focus briefly, while compiling some code or foraging for a snack, she found herself wondering what they were doing up there.
By process of elimination, it had to be something involving New Caird. They had already demonstrated that Ymir’s thrusters weren’t up to the task. Only New Caird’s main engine had enough thrust to make a difference. The problem was that it was pointed in one fixed direction, which didn’t happen to be the one in which they actually needed to push.
Following that chain of reasoning to its logical conclusion made her nervous, to the point where she was almost more distracted than she would have been had Markus and Slava been working in the same room with her.
She held her curiosity and her trepidation at bay until she was certain that the engine would have enough ice to achieve the apogee burn. Her work was finished. Half an hour remained. Jiro seemed to have his side of it under control.
A sharp thud, resounding through the walls of the command module, gave her an excuse to pull up some video and to eavesdrop on the audio channel that Markus and Slava were using. Robots salted all over Ymir’s exterior gave her eyes that she could turn in any direction. Even so, it took her a few minutes to obtain a picture of what was going on.
New Caird had undocked from Ymir and was nowhere to be seen. Presumably Markus was at her controls.
A man in a space suit was visible on the outside of Ymir, “walking” toward the stern by using a pair of Grabbs as mobile anchor points. This had to be Vyacheslav. His feet had sprouted thick white whiskers. It took Dinah a few moments to make sense of the image: he had zip-tied each foot to the back of a Grabb, and the “whiskers” were the protruding ends of the zip ties. It was the kind of improvisation that would have made old-school NASA engineers turn over in their graves, had the Hard Rain not eliminated that possibility. But in the last two years, and particularly the last two weeks, this kind of hillbilly engineering had become routine.
Which only made the question of what the hell Markus was up to more compelling. If Slava was being that creative with two robots and a sack of zip ties . . .