sed to be enmity between races because
they were different, and they tended to be different because they were
enemies, so there was enmity--The big problem of interstellar flight was
that nothing could travel faster than light, and nothing could travel
faster than light because mass increased with speed, and mass increased
with speed--obviously!--because ships remained in the same time-slot,
and ships remained in the same time-slot long after a one-second shift
was possible because nobody realized that it meant traveling faster than
light. And even before there was interstellar travel, there was
practically no interplanetary commerce because it took so much fuel to
take off and land. And it took more fuel to carry the fuel to take off
and land, and more still to carry the fuel for that, until somebody used
power on the ground for heave-off instead of take-off, and again on the
ground for landing. And then interplanetary ships carried cargoes. And
on Xosa II there was an emergency because a sandstorm had buried the
almost completed landing grid under some megatons of sand, and it
couldn't be completed because there was only storage power because it
wasn't completed, because there was only storage power because----

But it took three weeks for the problem to be seen as the ultimately
simple thing it really was. Bordman had called it a circular problem,
but he hadn't seen its true circularity. It was actually--like all
circular problems--inherently an unstable set of conditions. It began to
fall apart when he saw that mere refrigeration would break its solidity.

In one week there were ten acres of desert covered with
silicone-wool-felt in great strips. By day a reflective surface was
uppermost, and at sundown caterwheel trucks hooked on to towlines and
neatly pulled it over on its back, to expose gridded black-body surfaces
to the starlight. And the gridding was precisely designed so that winds
blowing across it did not make eddies in the grid-squares, and the
chilled air in those pockets remained undisturbed and there was no
conduction of heat downward by eddy currents, while there was admirable
radiation of heat out to space. And this was in the manner of the night
sides of all planets, only somewhat more efficient.

* * * * *

In two weeks there was a water yield of three thousand gallons per
night, and in three weeks more there were similar grids over the colony
houses and a vast roof