Another perigee was coming up soon. This time the nozzle would be aimed the way they wanted it—forward, once again turning the nuclear engine into a powerful retro-rocket. The robots on the inside of the shard had been at work scooping it out, sculpting the walnut-shell architecture that, according to the structural engineering simulations, would enable the whole thing to hold together during the last round of maneuvers. The hoppers were full of ice, with more on the way, and they’d finally learned how to make the system work consistently. Part of that lesson was not to try to accomplish too much with any one burn. It was better to take it easy, set a reasonable delta vee target, get it done and lock it down, then take stock of the situation and plan the next burn at leisure. Consequently their rendezvous with Izzy looked to be happening much later than they’d first expected, and almost every day brought a further postponement. But at the same time it came to seem more and more of a sure thing, less of a wild chance, and this began to affect Dinah’s thinking. Her robots were doing their work almost entirely on autopilot, leaving her somewhat bored. Vyacheslav, sealed up on the other side of a wall of plastic, could be talked to, but preferred keeping to himself. Jiro, on the other hand, had been working almost around the clock and had been showing signs of strain. Dinah would find excuses to float behind him and look over his shoulder at his screen. Was he playing solitaire? Running orbital mechanics simulations? Writing his memoirs? He seemed mostly to be looking at video feeds of machinery. By process of elimination, this had to be near the core of the reactor.