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.