Forty-eight hours, give or take a few minutes, now remained before Earth would loom huge below them, and the nadir surface of the shard would sweat and steam as the radiant heat shining up from the incandescent air softened, melted, and vaporized the ice. It was then that they would have to pull out the control blades and execute Ymir ’s next big burn. First they would have to spin the whole ship around so that she was flying "backward," her nozzle bell pointed in the direction of movement. For the delta vee they needed was a negative one—a braking, as opposed to accelerating, burn.