There was a mighty explosion at Skyharbor. The initial jolt which Marsh felt was much fiercer than the gradually built up speed of the whirling centrifuge in training. He was crushed deeply into his contour chair. It felt as though someone were pressing on his eyeballs; indeed, as if every organ in his body were clinging to his backbone. But these first moments would be the worst. A gauge showed a force of 7 G’s on him—equal to half a ton. He watched the Mach numbers rise on the dial in front of his eyes on an overhead panel. Each Mach number represented that much times the speed of sound, 1,090 feet per second, 740 miles an hour. Marsh knew “Big Tom” would blast for about a minute and a half under control of the automatic pilot, at which time it would drop free at an altitude of twenty-five miles and sink Earthward in a metal mesh ’chute. Marsh’s hurting eyes flicked to the outside temperature gauge. It was on a steady 67 degrees below zero Fahrenheit, and would be until he reached twenty miles. A reflecting prism gave him a square of view of the sky outside. The clear deep blue of the cloud-free stratosphere met his eyes. Mach 5, Mach 6, Mach 7 passed very quickly. He heard a rumble and felt a jerk. “Big Tom” was breaking free. The first hurdle had been successfully overcome, and the ship had already begun tilting into its trajectory. There was a new surge of agony on his body as the second stage picked up the acceleration at a force of 7 G’s again. Marsh clamped his jaws as the force pulled his lips back from his teeth and dragged his cheek muscles down. The Mach numbers continued to rise—11, 12, 13—to altitude 200 miles, the outer fringe of the earth’s atmosphere. There was a slight lifting of the pressure on his body. The rocket was still in the stratosphere, but the sky was getting purple. Mach 14—10,000 miles an hour. “Dick” would jettison any moment. Marsh had been aloft only about four minutes, but it had seemed an age, every tortured second of it. There was another rumble as the second stage broke free. Marsh felt a new surge directly beneath him as his own occupied section, “Harry,” began blasting. It was comforting to realize he had successfully weathered those tons of exploding hydrazine and acid that could have reduced him to nothing if something had gone wrong. Although his speed was still building up, the weight on him began to ease steadily as his body’s inertia finally yielded to the sickeningly swift acceleration. The speedometer needle climbed to Mach 21, the peak velocity of the rocket, 16,000 miles per hour. His altitude was 350 miles—man’s highest ascent. Slowly then, the speedometer began to drop back. Marsh heard the turbo pumps and jets go silent as the “lift” fuel was spent and rocket “Harry” began its free-flight orbit around Earth.