At 33,000 feet there was a momentary sensation as if the ship were tilted sharply. It wasn't. The instruments denied any change from level rise. The upward-soaring complex of flying things had simply risen into a jet-stream, one of those wildly rushing wind-floods of the upper atmosphere.
"Eastern velocity four hundred," said Mike from the communicator. "Now four-twenty-five.... Four-forty."
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.