The big armor-tender vibrated, gently and not unpleasantly, as the contragravity field alternated on and off. Sometimes it rocked slightly, like a boat on the water, and, in the big screen which served in lieu of a window at the front of the control-cabin, the dingy-yellow landscape would seem to tilt a little.

At three hundred miles an hour the Sandra had nicked the upper plates of the dome and streaked on, unharmed! It was not necessary now to use infra-red glasses to see the asteroid. It was there in the visi-screen for naked eyes, but for seconds not one of the men in the ship's control-cabin thought to look. The awful acceleration and shock had dazed them.

The hydrogen-fluorine combination is what passes for combustion here: the result is hydrofluoric acid, the local equivalent of water. The subsurface hydrogen is produced when the acid filters down through the rock, combines with pure metals underneath." The door at the rear of the control-cabin opened, and Juan Murillo, the seismologist, entered, followed by an assistant, who was not human.

Altamont gestured with his pipe toward the nuclear-electric conversion unit, between the control-cabin and the living quarters in the rear of the boxcar-sized helicopter. "We have enough power back there to keep this windmill in the air twenty-four hours a day, three hundred and sixty-five days a year, for the next fifteen years," he said. "We just don't have enough radio.