Stephen Baxter: Voyage

At forty thousand feet he reached .9 Mach, and he could feel a bumping, like a light airplane flying in turbulence. He was moving so quickly that the air molecules couldn’t get out of the way of his craft in time.

The turbulence smoothed out as he went supersonic.

Eighty thousand feet.

He moved the rocket’s throttle to maximum thrust, and he was pushed back into his seat by four and a half Gs. X-15-1 climbed almost vertically. The sky turned from pearl blue to a rich navy. He was already so high he could see stars ahead of him, in the middle of the day; so high there were only a few wisps of atmosphere, barely sufficient for his plane’s aerodynamic control surfaces to grip.

The sensations of power, of speed, of control were exhilarating.

Ninety thousand feet; thirty-two hundred feet per second.

The Mojave, spread out beneath him, over two thousand feet above sea level, was like the dried-out roof of the world.

Less than a minute into the flight, the problems started.

He got a message from the ground. It sounded like they were losing telemetry from the bird. The trouble was, the voice link had suddenly gotten so bad that he couldn’t tell for sure what they were saying.

A warning light showed up on his panel. Another glitch. For some reason his automatic reaction control rockets had deactivated. It wasn’t too serious yet; he was still deep enough in the atmosphere that he was able to maintain control with the aerodynamics.

The X-15 flew like an airplane in the lower atmosphere. It had conventional aerodynamic surfaces — a rudder and tail planes — which Stone could work electronically, or with his pitch control stick and rudder pedals. But above the atmosphere, the X-15 was a spacecraft. The automatic RCS reaction control system — little rocket nozzles, like a spaceship’s — was controlled by an electronic system called the MH96. And there was a separate manual RCS system Stone could control with a left-hand stick.

Quickly he was able to trace through the fault. The automatic RCS had shut itself off because the gains of his MH96, his control system, had fallen to less than 50 percent. The gains were supposed to drop when the plane was in dense air; then the MH96 was designed to shut itself off, to conserve hydrogen peroxide rocket fuel. But the gains had dropped because the hydraulics which controlled his aerodynamic surfaces were stuttering. So the automatic control system couldn’t rely on the data it was getting, and it had shut down the automatic RCS.

It looked as if the electrical disturbance that had started with the radio was spreading. Looks as if we might be snake-bit, old buddy.

Well, he was close to the exhaustion of his rocket fuel anyhow. He pressed a switch, and the engine shut down with a bang.

He was thrust forward against his straps, and then floated back.

He had gone ballistic, like a hurled stone; X-15-1 would coast to the roof of its trajectory, unpowered. He lost all sensation of speed, of motion. He was weightless inside the cabin, and he felt as if his gut were climbing up out of his neck.

He tried to put the problems aside. He was still flying, still in shape. And, no matter what was happening to the MH96, he had a program to work through, a whole series of experiments for NASA and the USAF.

One minute forty-one.

He activated the solar spectrum measurement gadget and the micrometeorite collector in his left wing pod.

Suddenly, the MH96 control system’s gains shot up to 90 percent, for no apparent reason, and the automatic RCS cut back in.

He checked his instruments. Like most experimental aircraft, the X-15’s cockpit had a primitive, hand-made feel, with rivets and wires showing. Well, it seemed he had full control ability for the first time since entering his ballistic flight path. He welcomed the return, but he was unnerved, all over again. What next?

He had very little confidence left in the battered old bird. Maybe she knows it’s her last flight; maybe she’d prefer a blaze of glory to a few decades rusting in some museum.

He would soon be going over the top, the peak of his trajectory, at 260,000 feet.

It was time to begin the precision attitude tracking work required for the solar spectrum measurement. He needed a nose-down pitch, and a yaw to the left. He was already flying at almost a zero-degree angle of attack, but was yawing a little to the right, and rolling off to the right as well. So he fired his wing-mounted roll control thruster for two seconds to bring his wings level, and his yaw control thruster to bring the X-15’s nose around to the left. The X-15 was like a gimbaled platform, hanging in the air, twisting this way and that in response to his commands. To stop the left roll he fired another rocket -

He was still rolling, too far to the left. Christ. What now?

The MH96 had failed again, and had cut out the automatic RCS, just as he was completing his maneuver.

He continued to rotate. To compensate he held his right roll control for eight more seconds. But the air was so thin that his aerodynamic controls were degraded, and the response was sluggish. He fired his manual RCS yaw rockets.

He could feel sweat pooling under his eyes; one problem after another was hitting him, blam blam blam.

Suddenly the MH96 cut back in with its automatic RCS. That stopped his yaw, short of the correct heading. Stone fired his manual yaw again; this time as he approached the reference heading the yaw was countered by the automatics, apparently correctly — but the damn thing cut out again, and he yawed past the reference.

And, on top of that, his roll attitude indicator ball was rotating. He had started rolling to the left again. He tried to wrestle that back with three short pulses on the manual roll RCS, but he overshot, and started a roll to the right…

Fifty miles high. The sky outside his tiny cabin was a deep blue-black, and the control lights gleamed brightly, like something off a Christmas tree. At the horizon’s rim he saw the thick layer of air out of which he’d climbed. He could see the western seaboard of the USA, all the way from San Francisco to Mexico; the air was clear, and it was all laid out under him like a relief map.

Three minutes twenty-three seconds. His yaw deviation was increasing, five or six degrees a second. And his heading had deviated from the B-52’s, maybe as much as fifty degrees. His angle was becoming extreme, and the air started to pluck at his aircraft, rolling it over to the right. He was in danger of rolling off completely. He might even reenter at the wrong attitude.

And if that happened, he’d finish up spread over the welcoming desert in a smoking ellipse one mile wide and ten miles long.

To stop the roll he applied left roll RCS, full left rudder and full left aileron. Everything he had. But the roll seemed to be accelerating. And the nose was starting to pitch down, too.

The starry sky, and the glowing desert below, started to wheel, slowly, around his cockpit, while he continued to work his controls.

At 240,000 feet above the ground — still supersonic — the X-15 went into a spin, tumbling around two axes at once.

He reported his spin to the ground.

They sounded incredulous. “Say again, Phil.”

“I said, I’m in a goddamn spin.” He wasn’t surprised at their disbelief; there was no way of monitoring the X-15’s heading from the ground, and they would only see pronounced and slow pitching and rolling motions.

And besides, nothing was known about supersonic spin. Nothing. There had been some wind tunnel tests on X-15 spin modes which had proved inconclusive.

There was no spin recovery technique in the pilot’s handbook.

Stone tried everything he knew, using his manual RCS and his aerodynamic controls. Full rudder; full ailerons. What else is there?