* * * * *

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]

The question was still open whether more shielding would be brought up
to make the overlap certain, or whether it would be best to maintain a
personnel rotation policy indefinitely. Some factions on Earth seemed
determined that rotation must remain not only a procedural but an
actual requirement--their voices spoke plainly through the directives
and edicts of U.N. Budget Control--but from what source behind this
bureaucratic smokescreen it would have been difficult to