al ability
of various gas molecules to "leak" through plastic membranes under
pressure, causing separation of the various molecular constituents of
the atmosphere; shunting carbon dioxide off in one direction, and
returning oxygen and the inert nitrogen and other gases back to the
surrounding atmosphere.

This latter method had proved highly satisfactory back on Earth, where
it was separating out fissionable materials in large quantities and
high purities from closely similar isotopes; and would now be tested
for efficiency versus weight in some of the new problems being
encountered in space.

A fourth method, direct chemical absorption by soda lime, had been
discarded early in the program, although it was still used in
spacesuit air cleaners, and for the duration of the canned air program
under which they were now operating.

The lab was like that--no problem has a single solution. And it was
the lab's job to evaluate as many solutions as possible so that the
best, under different conditions, might be proved and ready for use in
later programs.

* * * * *

Paul Chernov, ordinary spaceman--which meant that he had only a little
more specialized training than the average college graduate--was
working in the dump, surrounded by much of the equipment that remained
to be placed aboard Space Lab One, and trying to identify the
particular object he sought.

Looking down almost directly over the eastern bulge of the African
coast, he sighted what was probably the ECM lathe he was after, and
kicked towards it, simultaneously pulling his pistol-gripped Rate of
Approach Indicator from the socket in his suit.

The RAI gun, he sometimes felt, was the real reason he'd become a
spaceman in these tame days. Even if he couldn't be a space pirate, it
gave him the feel.

Humming to himself, he aimed the search beam from the tiny
gallium-arsenide laser crystal that was the heart of the gun at the
bulky object, and read off the dial at the back of the "barrel" the
two meter/second approach velocity and the twenty-eight meter
distance.

He could as easily have set the RAI gun to read his velocity and
distance in centimeters or kilometers, and it would have read as well
his rate of retreat, if that had been the factor.

Paul's RAI gun might be, to others, a highly refined, vastly superior
great-grandson of the older radar that had required much more in the
way of equipment than the tiny bulk of th