Major Philip Stone joined the USAF in 1953, at the age of twenty. He arrived in Korea in time to make a series of hazardous sorties. Well, Korea had been a turkey shoot. But Stone hadn’t enjoyed combat. His buddies called him too serious — a straight arrow. But for Stone, the important thing was what he could learn in each flight, either about his machines or about himself.

After the war, his disciplined curiosity found a new focus.

In the early 1960s the most promising route to space, if you were inside the USAF, had looked like the experimental high-altitude rocket aircraft program. The X-15s could even give their pilots astronaut wings, by flying through the officially recognized lower limit of “space,” at fifty miles high. The X-15s were to lead to the advanced X-20 — the Dyna-Soar — in which a guy would have been boosted into orbit, and then he would have flown back down, landing like an airplane.

But with men routinely being hurled into space in ballistic capsules like Mercury and Gemini, the X-20 looked too advanced for its time, and it soon ran up a bill as large as that for the entire Mercury program without delivering a single flight article. And it was canned.

Now, the only way for a pilot to reach space was to transfer to NASA. Neil Armstrong was another X-15 pilot who had gone that way before. And so that was what Stone had determined to do.

But first he had some unfinished business.

In 1969, Stone was thirty-seven years old.

“Drop minus one minute.”

“One minute,” Stone said. “Rog. Data on. Emergency battery on. I’m ready when you are, buddy. Master arm is on, system arm light is on…”

The B-52 reached its launch station over Delamar Dry Lake in Nevada. The rocket plane was suspended from the bomber’s wing pylon like a slim, black, stub-winged missile, crammed full of liquid oxygen and anhydrous ammonia, ready for its midair launch.

Stone was sealed up inside the X-15. The B-52’s engine was just feet away from his head, but Stone, cocooned inside the pressurized cockpit, could barely hear its noise. From the corner of his eye he could see the chase planes clustered close to the B-52. At last, this damn flight is going to be over and done with.

After fifteen years, the X-15 program was winding up. There was only one serviceable ship left: X-15-1, the first to fly back in 1960, a veteran of seventy-nine previous missions. The Edwards people wanted to finish up the program with one last flight, the two hundredth overall; and they had asked Phil Stone to stay around long enough for that. But then there was a series of delays and technical hitches, and the winter weather had closed in, until the flight was all but a year later than it had originally been planned for.