"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 defenseless against it. Nobody could even hope for world domination so long as it floated on its celestial round. Which, naturally, was why there were such desperate efforts to destroy it before its completion. But Joe, thinking about the Platform, did not think about it as a weapon. It was the first rung on the stepladder to the stars. From it the moon would be reached, certainly. Mars next, most likely. Then Venus. In time the moons of Saturn, and the twilight zone of Mercury, and some day the moons of Jupiter. Possibly a landing could be dared on that giant planet itself, despite its gravity. The co-pilot spoke suddenly. "How do you rate this trip by cargo plane?" he asked curiously. "Mostly even generals have to go on the ground. You rate plenty. How?"