“Copy that, Tom. Columbia, everything looks good to us. You are still go for the deorbit burn.”

Lamb replied, “That’s the best news we’ve had in sixteen days.”

Angel said, “The Earth is real beautiful up here, pal. I wish you could see how beautiful it was…”

“Okay, let’s go for APU start,” Lamb said. “Number one APU fuel tank valve to open.”

“Number one APU control switch to start. Hydraulic pump switches to off.”

“Confirm I got a green light on the hydraulic pressure indicator. Houston, Columbia. We have single APU start, over.”

“Copy that. The APUs were big hydrazine-burning auxiliary power units. They powered the orbiter’s hydraulics system. During the launch, they had swivelled the big main engines, and now they would be used to adjust Columbia’s aerosurfaces during the descent. During its glide down the orbiter would be reliant on the APUs; without them, and without engines to provide power, it would have no control over its fall to Earth. The power units were clustered in the orbiter’s tail, beneath the pods of the OMS — rhyming with “domes,” the smaller orbital maneuvering system engines which would slow Columbia out of its orbit.

“Okay, let’s arm those babies,” Lamb said. “Digital pilot to auto mode.”

“Left and right OMS pressure isolation switches to GPC. Engine switches to arm/press.”

“Gotcha. Houston, OMS engines are armed, over.”

“Roger, you are go for burn countdown.”

Lamb scratched the silvery stubble on his cheek. He looked sideways at Angel. “What do you say? Shall we fire these old engines, or take another couple of swings around the bay?”

“Aw, I’m done sightseeing.”

Lamb pressed the EXEC button on his computer keyboard. “Five. Four. Three. Two.”

There was a jolt, and a remote rumble, and then a steady push at Benacerraf’s back.

The CRT displays cycled between a complex display of the orbiter’s horizontal position, and a burn status screen.

“…Hey.” Angel shifted; something about his body language changed. He was looking at a panel in front of him. “I got a warning on prop tank pressure, in the right OMS engine pod.”

“High or low?”

“High. Two eighty-five psi.”

Lamb grunted. “Well, the relief valve should blow at two eighty-six. Anyhow, we only need another few minutes.”

The burn continued.

Fahy’s controllers saw the excess pressure immediately.

“Flight, Prop.”

“Go.”

“I’ve got some anomalies in the right-hand OMS engine pod. The relief valve has just blown and resealed, the way Tom said. That brought us down to the operating range. But now I’m seeing a pressure rise again.”

“Will we get through the burn?”

“Uncertain, Flight. The trend is unsteady.”

“All right. Anyone else got anything in that OMS engine pod? EECOM, how about you?”

“Flight, EECOM. The temperature in there looks okay. I guess the heaters have been functioning.”

“You guess?”

“Flight, the data looks a little flat to me…”

That meant the environment control people thought they might be seeing some kind of instrumentation fault with the wraparound heaters which kept the fuel lines from freezing up.

Fahy wasn’t too worried by the anomaly, obscure as it was. At the back of the orbiter, in the OMS engine pods, was a complex, interconnected system of engines and fuel and oxidizer tanks. For safety the tanks were situated in the two separate OMS engine pods, on either side of the orbiter. But they could feed, through isolation valves and crossfeed lines, both the big orbital maneuvering engines and the smaller reaction control engines in either pod.

Even if there were a real tank defect of some kind in the right pod, it was highly unlikely that it could affect the left pod. The left pod’s tanks could then keep feeding both left and right OMS engines through the pod crossfeed lines. If the defect were severe enough to kill the right OMS engine itself, the left engine could keep firing to complete the burn. And even if both OMS engines were lost, the smaller reaction control engines maneuvering jets could fire and maintain the burn, using up the excess OMS propellant.

There was a lot of redundancy in Shuttle.

It was a nagging worry, though.

She knew that those OMS engine pods, and their contents, were rated for a hundred flights; the pods flying today had completed eight and nine flights respectively. But the refurbishment schedule had been cut down in the last couple of years, by the United Space Alliance, the private consortium to which Shuttle ground operations had been outsourced.

She made a mental note to recommend the strip-down of that right OMS engine pod, maybe the left as well.

There were only a couple of minutes left in the burn anyhow. She watched the big mission clock on the display/control screen at the front of the FCR, counting down to the end of the burn.

That was when the master alarm sounded.

The flight deck was filled with a loud, oscillating tone. Four big red push-button alarm lights lit up on the instrument panels around the cabin.

Lamb pushed a glowing button on a central panel, above a CRT; the lights and the tone died. “Now what the hell?”

Benacerraf heard her breath scratch in the confines of her helmet.

A master alarm. Shit.

…But, she realized, the tone hadn’t been a siren, which would have been set off by the smoke detection system, or a klaxon, which would have meant loss of cabin pressure.

Whatever was coming down, it couldn’t be as bad as that, at least.

She tried to steady her breathing. She was supposed to be here to help, after all.

At the center of the cockpit consoles there was a forty-light caution/warning display. A small panel marked “right OMS” glowed red. The engine, then.

Angel said. “I think—”

There was a jarring bang, sharp and abrupt.

The orbiter shuddered; Benacerraf felt the rattle through her canvas seat, and she heard the creak of stressed metal. Long-wavelength vibrations washed along the structure of the orbiter, powerful, energy-dense.

She could feel it. The thrust of both OMS engines had died, halfway through the burn.

The master alarm sounded again. Now both left and right OMS lights on the caution/warning light array glowed red.

Lamb killed the noise with a stab at a red button. “Goddamn squawks.”

Angel seemed to have frozen; he turned to Lamb, his mouth open. That bang was like a howitzer in the back yard. What was it, some kind of hard light?”

Lamb was pressing at an overhead panel. “Losing OMS pressure,” he barked. “Losing OMS propellant.”

Angel seemed to come to himself. “Okay. Uh, Houston, we seem to—”

“Houston, Columbia,” Lamb broke in. “We have a situation up here. We lost OMS.”

The master alarm sounded again; Lamb killed it again.

It was like the worst simulation in the world, Benacerraf thought.

Tell me this isn’t happening, Fahy thought. She stared at the numbers on her screen, at the flickering alarm indicators, unable, for the moment, to act — unable, in fact, to believe her eyes.

The capcom said, “Can you confirm that, Columbia?

“We lost both OMS, halfway through the burn.”

“Copy that.”

The capcom — a balding trainee astronaut called Joe Shaw — turned and looked to her for guidance, for instructions on what to say next.

Fahy tried to think.

“EECOM, tell me what you got.”

“I see a sealed can, Flight.”

EECOM was telling her that the spacecraft was intact; the crew still had a life-sustaining environment. That was always the first priority, in any situation like this. It gave her time to react.

“DPS, how about you?”

“We think there’s maybe a telemetry problem with a wraparound heater.”