rce. Each was plated with iridium
lest a speck of rust form and throw it off balance. If the shaft and
bearings were not centered exactly at the center of gravity of the
rotors--five hundred pounds of steel off balance at 40,000 r.p.m. could
raise the devil. They could literally wreck the Platform itself. And
"exactly at the center of gravity" meant exactly. There could be no
error by which the shaft was off center by the thousandth of an inch, or
a ten-thousandth, or even the tenth of a ten-thousandth. The accuracy
had to be absolute.

Gloating over the solution he'd found, Joe could have hugged himself.
Hanging to a strap in the waiting bus, he saw another bus start off with
a grinding of gears and a spouting of exhaust smoke. It trundled to the
highway and rolled away. Another and another followed it. Joe's bus fell
in line. They headed for Bootstrap in a convoy, a long, long string of
lighted vehicles running one behind the other.

It was dark outside. The Shed was alone, for security. It was twenty
miles from the town where its work force slept and ate and made merry.
That was security too. One shift came off, and went through a security
check, and during that time the Shed was empty save for the security
officers who roamed it endlessly, looking for trouble. Sometimes they
found it. The shift coming on also passed through a security check.
Nobody could get into the Shed without being identified past question.
The picture-badge stage was long since passed on the Space Platform job.
Security was tight!

The long procession of busses rolled through the night. Outside was dark
desert. Overhead were many stars. Inside the jammed bus were swaying
figures crowded in the aisle, and every seat was filled. There was the
smell of sweat, and oil, and tobacco. Somebody still had garlic on his
breath from lunch. There was the noise of many voices. There was an
argument two seats up the aisle. There was the rumble of the motor, and
the peculiar whine of spinning tires. Men had to raise their voices to
be heard above the din.

A swaying among the crowded figures more pronounced than that caused by
the motion of the bus caught Joe's eye. Somebody was crowding his way
from the back toward the front. The aisle was narrow. Joe clung to his
strap, thinking hard and happily about the rebalancing of the gyros.
There could be no tolerance. It had to be exact. There had to be no
vibration at all....

Figures swayed away from him. A