timate speed they could
manage. They'd fired jato rockets, all at once, and so pushed its speed
up to the preposterous. Then they'd dropped away and the giant steel
thing had fired its own rockets--which made mile-long flames--and swept
on out to emptiness. Before its rockets were consumed it was in an orbit
4,000 miles above the Earth's surface, and it hurtled through space at
something over 12,000 miles an hour. It circled the Earth in exactly
four hours, fourteen minutes, and twenty-two seconds. And it would
continue its circling forever, needing no fuel and never descending. It
was a second moon for the planet Earth.

But it could be destroyed.

Joe watched hungrily as it went on to meet the sun. Smoothly,
unhurriedly, serenely, the remote and twinkling speck floated on out of
sight. And then Joe went back to the table and ate his breakfast
quickly. He wolfed it. He had an appointment to meet that minute speck
some 4,000 miles out in space. His appointment was for a very few hours
hence.

He'd been training for just this morning's effort since before the
Platform's launching. There was a great box swinging in twenty-foot
gimbal rings over in the Shed. There were motors and projectors and over
two thousand vacuum tubes, relays and electronic units. It was a space
flight simulator--a descendant of the Link trainer which once taught
plane pilots how to fly. But this offered the problems and the
sensations of rocketship control, and for many hours every day Joe and
the three members of his crew had labored in it. The simulator
duplicated every sight and sound and feeling--all but heavy
acceleration--to be experienced in the take-off of a rocketship to
space. The similitude of flight was utterly convincing. Sometimes it was
appallingly so when emergencies and catastrophes and calamities were
staged in horrifying detail for them to learn to respond to. In six
weeks they'd learned how to handle a spaceship so far as anybody could
learn on solid ground--if the simulator was correctly built. Nobody
could be sure about that. But it was the best training that could be
devised.

In minutes Joe had finished the coffee and was out of Major Holt's
quarters and headed for the Shed's nearest entrance. The Shed was a
gigantic metal structure rising out of sheer flat desert. There were
hills to the westward, but only arid plain to the east and south and
north. There was but one town in hundreds of miles and that was
Bootstrap, b