WORK GAVE THEM SOMETHING TO DO DURING THE FINAL ORBIT OF the Big Ride besides worry about what was going to happen at the end of it. The huge burn that they would make at apogee, combining a final plane change with an acceleration into the “fast lane” where Cleft rolled around the world like a ball bearing in a tire, contained so many unfathomable chances that it beggared prediction. The new wrinkle, however, was this: since they would be moving into a stream of rocks moving faster than they were, the rocks would be coming at them from behind, where Amalthea had no power to protect them.
Early in the mission Doob had dreamed of reconfiguring Endurance at the last minute, moving the vulnerable stuff around to the asteroid’s other side. With the manpower they’d had in those days, it might have been possible. As it was, reduced to a crew of twenty-eight starvelings, it was out of the question. It took all the people they had to make accommodations for the Swarm’s heptad. They would dock it in the middle of the Stack, lock it in place with a few cables, and hope it stayed attached during the subsequent maneuvers. They would keep the hatch closed. The eleven members of A?da’s group would simply stay in their arklets until it was all over. The justification was that they’d be safer there. The true reason was that no one wanted cannibals in the shared spaces of Endurance.
The big project for Dinah, and for the small remnant crew of robot jockeys who tended to work with her, was getting ready to dump Amalthea itself.
On one level the idea seemed nearly unthinkable. They had, however, been planning to do it for a long time. Endurance’s final series of maneuvers would have to be accomplished quickly, deftly, in an environment where the rocks tended to be much larger than the ones that made up the Hard Rain. In a sense, the boulders up there were the mothers of the tiny fragments that had destroyed the surface of Earth. Every time two of them collided, a few chips exploded outward from the impact, and a fraction of those ended up falling into Earth’s atmosphere. The Hard Rain would continue until all of them had been reduced to sand and organized themselves into a neat system of rings. In any case, Amalthea’s ability to protect Endurance from the impacts of baseball-or even basketball-sized rocks was of little interest in a place where a rock the size of Ireland would be considered unremarkable. The entire ship, Amalthea and all, would be a bug on the windshield of such a thing. Their only way to stay alive, once they had entered the slipstream of the main debris cloud, was to maneuver around the big rocks and hope that they didn’t get hit by too many little ones during their dash to Cleft. And that sort of maneuvering was impossible as long as Amalthea—which weighed a hundred times as much as the rest of Endurance—was attached to her.
In addition to Amalthea, Endurance was still burdened by a considerable mass of ice, which they had hoarded both as shielding and as propellant. It weighed a significant fraction of what Amalthea weighed. But unlike Amalthea, they could burn it. The basic plan was to split most of that ice into hydrogen and oxygen, then burn it during the final speed-up at apogee. Over the course of a few hectic minutes, Endurance would expend most of her water weight by using it as propellant. Between that and the ditching of Amalthea, her total weight would drop by a factor of more than a hundred in the course of an hour. After that, she truly would be like a bug flitting around in heavy traffic, dodging big rocks and taking hits from little ones until she made her way to Cleft.
In any case, they had anticipated all of this long ago. Dinah and the other surviving members of the Mining Colony had had three years in which to reshape Amalthea from the inside. Seen from the forward end, the asteroid looked the same as ever. Internally, however, most of it had systematically been whittled loose. In a sense the process had begun around Day 14, when Dinah had set one of her Grabbs to work carving out a niche in which she could stash her electronic parts. Since then it had proceeded in fits and starts. They’d moved a lot of metal in order to make a storage bay for Moira Crewe’s genetic equipment, which in a sense was the raison d’être of everything else they had done in the last three years. Once that was safe they had begun tidying up, enlarging the pockets of protected space, breaking down walls, and joining them together into a cylindrical capsule scooped out of Amalthea’s back, called the Hammerhead for the way it lay athwart the top of the Stack.
Thanks to a lot of ticklish work by robots in the last couple of years, the Hammerhead was now separated from the rest of Amalthea—99 percent of the asteroid’s bulk and mass—by walls of nickel-iron that were only about as thick as the palm of a person’s hand. This still made them extremely massive by the standards of space architecture—more than strong enough to hold in atmospheric pressure and to stop small bolides. But the additional tens of meters’ thickness of metal beyond those walls was now physically detached from the hand-thick walls, and could be pushed away by a puff of compressed air.