ced the
long runway, a tinny voice from the control tower spoke out of a
loud-speaker under the instruments, and the plane roared down the field.
In seconds it lifted and swept around in a great half-circle.

"Okay," said the pilot. "Wheels up."

The co-pilot obeyed. The telltale lights that showed the wheels
retracted glowed briefly. The men relaxed.

"You know," said the co-pilot, "there was the devil of a time during the
War with sabotage. Down in Brazil there was a field planes used to take
off from to fly to Africa. But they'd take off, head out to sea, get a
few miles offshore, and then blow up. We must've lost a dozen planes
that way! Then it broke. There was a guy--a sergeant--in the maintenance
crew who was sticking a hand grenade up in the nose wheel wells. German,
he was, and very tidy about it, and nobody suspected him. Everything
looked okay and tested okay. But when the ship was well away and the
crew pulled up the wheels, that tightened a string and it pulled the pin
out of the grenade. It went off.... The master mechanic finally caught
him and nearly killed him before the MPs could stop him. We've got to be
plenty careful, whether the ground crews like it or not."

Joe said drily: "You were, except when they were topping off. You took
that for granted." He told about the sandy-haired man. "He hadn't time
to stick anything in the wheel well, though," he added.

The co-pilot blinked. Then he looked annoyed. "Confound it! I didn't
watch! Did you?"

The pilot shook his head, his lips compressed.

The co-pilot said bitterly: "And I thought I was security-conscious!
Thanks for telling me, fella. No harm done this time, but that was a
slip!"

He scowled at the dials before him. The plane flew on.

This was the last leg of the trip, and now it should be no more than an
hour and a half before they reached their destination. Joe felt a lift
of elation. The Space Platform was a realization--or the beginning of
it--of a dream that had been Joe's since he was a very small boy. It was
also the dream of most other small boys at the time. The Space Platform
would make space travel possible. Of course it wouldn't make journeys to
the moon or planets itself, but it would sail splendidly about the Earth
in an orbit some four thousand miles up, and it would gird the world in
four hours fourteen minutes and twenty-two seconds. It would carry
atom-headed guided missiles, and every city in the world would be
defense