But the computer had already taken over, and was controlling the flow of water to the hydrostatic balance tank system, rapidly orienting the axis of spin against the true axis of the wheel. The wobble became a wiggle; the wiggle became the slightest of sways; and under the computer's gentle ministrations, the sways disappeared and Space Lab One rolled true. Slowly Mike inched the jet power up, and the speed and "gravity" of the rim rose--from 0.009 to 0.039 to the pre-scheduled 0.15 of a gravity--two RPM--at which she would remain until a thorough test schedule over several days had been accomplished. Later tests would put the rim through check-out tests to as high as 1.59 gee, but "normal" operation had been fixed at two RPM. In the background, the susurrus of the air jets rose slightly to the soft lullaby-sound that the wheel would always sing as she rolled. * * * * * New, experimental, her full complement of six hundred scientists and service personnel so far represented by only one hundred sixty-three aboard, the big wheel that was Space Lab One rotated majestically at her hydrodynamically controlled two revolutions per minute. She gave nearly half her mass to the water that spun her--huge rivers of water, pumped through the walls of the wheel's rim, forming a six-foot barrier between the laboratories within the rim and the cosmic and solar radiations of outer space. Arguments on Earth had raged for months over the necessities--or lack of them--for the huge mass of water aboard, but the fluid mass served many purposes better than anything else could serve those purposes. As a radiation shield, it provided sufficient safety against cosmic radiations of space and from solar radiations, except for solar flare conditions, to provide a margin of safety for the crew over the three months in which they would do their jobs before being rotated back to Earth for the fifteen-month recovery period. The margin was nearly enough for permanent duty--and there were those who claimed it was sufficient--but the claim had not been substantiated, and the three months maximum for tour was mandatory. Originally, shielding had not been considered of vital importance, but experience had proven the necessity. The first construction personnel had been driven back to Earth after two weeks, dosimeters in the red. The third crew didn't make it. All five died of radiation exposure from a solar flare. An original two weeks' limit was raised as more shielding arrived--three weeks, four, five--now the shadowy edge of the theoretic ninety-day recovery rate from radiation damage and the ninety days required to get the maximum safe dosage overlapped--but safety procedures still dictated that a red dosimeter meant a quick return to Earth whether the rate of recovery overlapped or not. [Illustration]