JETTISON did her the courtesy of showing a countdown on the screen, so that she could plug her ears. When it hit zero, a sickening crack resounded through the whole structure. The video feed showed a brilliant spray of ice blown free from the central pillar, just above where it connected to the reactor vessel. Demolition charges, placed there long ago by Sean’s crew, had detonated and severed the connection. For a moment she feared nothing further would happen, but then jets of white steam lanced from the reactor vessel’s rounded top. JETTISON had opened valves, releasing pressure that had built up in the chamber from the reactor’s residual heat, and those valves were now acting as makeshift rocket engines, pushing the whole reactor, and everything attached to it, down toward the vacancy of the nozzle.