There was a 300-mile-an-hour wind behind them. A tail-wind, west to east. The pushpots struggled now to get the maximum possible forward thrust before they rose out of that east-bound hurricane. They added a fierce push to eastward to their upward thrust. Mike's cracked voice reported 500 miles an hour. Presently it was 600. At 40,000 feet they were moving eastward at 680 miles an hour. A jet-motor cannot be rated except indirectly, but there was over 200,000 horsepower at work to raise the spacecraft and build up the highest possible forward speed. It couldn't be kept up, of course. The pushpots couldn't carry enough fuel. But they reached 55,000 feet, which is where space begins for humankind. A man exposed to emptiness at that height will die just as quickly as anywhere between the stars. But it wasn't quite empty space for the pushpots. There was still a very, very little air. The pushpots could still thrust upward. Feebly, now, but they still thrust. Mike said: "Communications says get set to fire jatos, Joe." "Right!" he replied. "Set yourselves." Mike flung a switch, and a voice began to chatter behind Joe's head. It was the voice from the communications-room atop the Shed, now far below and far behind. Mike settled himself in the tiny acceleration-chair built for him. The Chief squirmed to comfort in his seat. Haney took his hands from the equalizing adjustments he had to make so that Joe's use of the controls would be exact, regardless of moment-to-moment differences in the thrust of the various jets. "We've got a yaw right," said the Chief sharply. "Hold it, Joe!" Joe waited for small quivering needles to return to their proper registrations. "Back and steady," said the Chief a moment later. "Okay!" The tinny voice behind Joe now spoke precisely. Mike had listened to it while the work of take-off could be divided, so that Joe would not be distracted. Now Joe had to control everything at once. The roar of the pushpots outside the ship had long since lost the volume and timbre of normal atmosphere. Not much sound could be transmitted by the near-vacuum outside. But the jet motors did roar, and the sound which was not sound at such a height was transmitted by the metal cage as so much pure vibration. The walls and hull of the spaceship picked up a crawling, quivering pulsation and turned it into sound. Standing waves set up and dissolved and moved erratically in the air of the cabin. Joe's eardrums were strangely affected. Now one ear seemed muted by a temporary difference of air pressure where a standing wave lingered for a second or two. Then the other eardrum itched. There were creeping sensations as of things touching one and quickly moving away. Joe swung a microphone into place before his mouth. "All set," he said evenly. "Brief me." The tinny voice said: