The second complication was the ship’s slow tumble. This meant that their nuclear rocket engine was never pointed in the right direction, save by lucky accident. During the big burn at perigee, they had wanted the nozzle pointed forward, so that it would serve as a huge retro-rocket. The upcoming burn at apogee was intended to speed her up a bit, and so they needed the nozzle pointed aft. But as long as she tumbled, it was aimed in no particular direction.