Soon he would be accelerating at multiple Gs, which meant adding ninety miles per hour every second.

He’d forgotten how impressive an aircraft X-15 was.

“Should be coming up on alpha,” the ground said.

Seven seconds. Deeke turned three degrees to the right to correct his heading. He kept one eye on the cockpit clock. Nine seconds. Ten seconds. Timing was everything in an X-15 flight. He checked his angle of attack, angle of sideslip, roll attitude, rate of climb.

Fifteen seconds. The acceleration looked nominal, still under two G. He watched his pitch attitude vernier needle, which was stalling to come off its peg. Here it came, at eighteen seconds, moving towards the null position. At twenty seconds the needle was centered and he eased off on his angle of attack, to maintain the planned twenty-five-degree climb angle.

“You should be on pitch attitude now,” the ground said.

“Rog. Track looks real good. I feel as if I’m back in the saddle again. I wish I could do a barrel roll.”

“Rog that,” the ground said anonymously.

Yeah. You aren’t here to enjoy this, Linebacker.

At fifty thousand feet he shot through a layer of grey, hazy cloud. He emerged into a blue, infinite sky. The sun was still low, and it cast shadows on the ocean of cloud beneath him, which obscured the Earth.

He looked ahead, half expecting to see the Shuttle’s vapor stack, ahead of him; but his tipped-up windows showed him nothing but sky.

The handover from the KSC Firing Room had been as smooth as Barbara Fahy could have asked for. She didn’t even have to say anything. The ascent, complex and dangerous as it was, was just a process, she reflected, something they had handled more than a hundred times before, unfolding now with the inevitability of the logic of a well-tested software program.

Only the brilliant rocket light on the projected display at the front of the room gave any hint of the violence of the events the FCR’s devices were monitoring.

Even so, Fahy found it difficult to breathe.

…Now a new voice sounded in her ear. It was the range safety officer. It seemed that some unknown aircraft had wandered into the exclusion zone around the ascent profile.

Benacerraf looked ahead, out of the window beyond Angel. A layer of cloud hurtled at the orbiter like a wall. Endeavour shot through in a second, and emerged under a deep blue, dome-like sky.

Angel closed switches, configuring the attitude indicator before him.

“There’s Mach point nine,” Libet said. “Okay, Mach one. Going through nineteen thousand.”

Forty seconds, Benacerraf thought, to reach the speed of sound from a standing start.

“Forty-four seconds.”

“Houston, Endeavour. Max Q. Into the throttle bucket.”

Max Q was a moment of danger, Benacerraf knew, the moment at which the Shuttle stack’s gathering velocity, coupled with the still-high density of the air, exerted maximum aerodynamic pressure on the airframe. The main engines had briefly throttled down to relieve the pressure.

“Copy,” Marcus White called. “Fifty-seven seconds. Endeavour, Houston. You are go for throttle up.”

“Copy that. Throttle up.”

“Wow,” Libet said, “feel this mother go.”

“Sixty-two seconds,” White said.

“Thirty-five thousand,” Angel said. “Going through Mach one point five.”

“Here we go,” Libet said. “SRB pressure is dropping.”

Already the solid rocket boosters were burning out.

“One minute fifty,” White called up. “Twenty-one miles high, eighteen miles down range. Houston, Endeavour. Pressures less than fifty psi.”

“Copy.”

“SRB burnout.”

As the solid boosters died, it felt to Benacerraf like a dip, as if the Shuttle was suddenly falling out of the sky, just for a second. But then the acceleration built up powerfully once more.

“Ready for SRB sep.”

“Roger.”

There was a bang and a bright flash, beyond the orbiter’s panoramic windows, as the boosters’ separation motors ignited. It was as if she flew through a fireball.

“Okay, Linebacker, we have you right on track, on the profile.”

“Rog.”

Thirty-one seconds. The rocket burn roared on. Deeke worked his way around checks of his engine instruments, hydraulic pressures, generators, APU temperatures, stabilizer positions, crosschecking his altitude and velocity and rate of climb.

Thirty-five seconds. He shifted in his seat slightly, trying to get more comfortable; the G was already above two and was climbing fast.

“Stand by for eighty-three thousand feet.”

“Rog, eighty-three thousand.” Now his altitude too was piling up rapidly.

“Do you still read us, Linebacker?”

“Affirm.”

“Coming up on a hundred and ten thousand.”

“Hundred and ten, affirm.”

“On the profile, on the heading. On the profile.”

A minute fifteen.

He was already above the bulk of the sensible atmosphere. Ahead and all around him, the sky started to turn from a pearl blue to a deeper, dark blue. His vision seemed to stretch to infinity, to the gently curving, blue-white horizon; there was very little dust or mist above him.

The G forces were reaching their peak now — constant thrust combined with reducing aircraft mass to drive the acceleration higher — he was almost up to four G. This wasn’t excessive, Deeke knew, but it hurt his ageing chest; he felt he had to fight to take a breath.

“Stand by for shutdown.”

“Standing by.”

The airframe popped and banged, its skin panels buckling and cracking as he climbed through four G. He’d heard such noises before. The pilots used to call it the oil-can effect. Outside air would work its way into the aircraft through small gaps in external doors or panels; the air was like a torch at high speeds, and would burn electrical wiring, aluminum internal structure and metal tubing, and smoke would waft into the cockpit.

But the X-15, even after decades in a museum, was a tough old bird.

A minute twenty-three. Deeke closed the shutdown switch.

The roar of the engine tailed off into a high-pitched, hog-calling squeal, then ceased.

Suddenly he was weightless; he was thrown forward against his restraints, and he felt his stomach lurch within him.

He was gliding, at almost five Mach, a stone hurled from a catapult.

Now Deeke took his left-side stick, to work the RCS manual controls. He dipped the nose of the X-15.

The horizon rose over the lip of the mailbox window before him. My God, he thought. I’m too damn old for this.

Earth was a brilliant blue floor beneath him, set beneath a darkened sky. To his left and right, he could make out the whole of the eastern seaboard of the U.S., from New York bay to his left, Florida obscured by its ragged coating of cloud below him, and to his right, set in the glittering blue skin of the ocean, a lumpy, brown-green mass that must be Cuba. He was still climbing, thrown by the rocket thrust out of the atmosphere like a stone. The curvature of the planet was clearly visible, as was the layer of denser atmosphere that surrounded it.

And, directly ahead of him, a pillar of orange-white vapor came climbing out of the atmosphere, filled with bright sunlight, arcing gracefully away from him. At the tip of the pillar there was a jewel of yellow-white light, a droplet of brilliance brighter than the sun itself.

The stark simplicity of that thrust out of gravity’s bonds was unbearably beautiful, astonishing, like a direct challenge to God.

Through gaps in the cloud Jackie could see the solid rockets fall away from the stack, still trailing dribbles of smoke and flame. There was a ragged cheer from the stand behind her.

Once started, the solid rockets couldn’t be stopped or throttled down, unlike liquid boosters; once the solids were lit, the orbiter — and its crew and that huge explosive tank of hydrogen and oxygen strapped to its belly — were just along for the ride, until the SRBs expended themselves.