John Hall wiped away blood that trickled from his mouth. Painstakingly he disengaged himself from the hopeless wreckage of the control room. He staggered free, his lungs pumping with terrific effort to draw enough oxygen from the thin, bitterly cold air of Ganymede—that had rushed in when his helmet had been shocked open. Feeling unusually light he walked over to an enormous tear in the side of his space-cruiser. A bleak scene met his eyes. Short, grotesquely hewn hills and crags. Rocky pitted p