Titan. Stephen Baxter
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 manoeuvring 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 manoeuvring 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.’
‘Where?’
‘On one of the right OMS engine pod propellant lines.’
‘EECOM, you got a comment on that? It’s your heater.’
‘It’s possible, Flight. That heater might be down. We don’t have the data.’
In which case that fuel line could be frozen. Or melting, depending on the situation.
‘All right. Prop, talk to me.’
‘Prop’ was the propulsion engineer. ‘I’ve lost nitrogen tet and hydrazine pressure in the OMS tanks,’ Prop said miserably. Nitrogen tetroxide was the oxidizer, monomethyl hydrazine the fuel for the OMS engines. ‘If my telemetry’s right.’
‘Which tanks?’
‘Both.’
‘What? Both pods? But they’re on opposite sides of the bird.’ And besides, the OMS engines – because of their importance – were among the simplest systems in the orbiter. They were hypergolic; fuel and oxidizer ignited on contact, without the need for any kind of ignition system, unlike the big main engines. There was hardly anything that could go wrong. ‘How the hell is that possible?’
‘We’re working on that, Flight.’
‘How much of a loss are you seeing?’
‘I’m down to zero. It’s as if the tanks don’t exist any more. There has to be some telemetry screw-up here.’
But we have that report from Lamb, she thought. We know the OMS have shut down. This is something real, physical, not just telemetry.
Another call came in. ‘Flight, EGIL. I got me an unhappy power unit. Number two is in trouble.’
‘What’s the cause?’
‘We can’t tell you that yet, Flight.’
‘Can you keep it on line?’
‘For now. Can’t tell how long. Anyhow performance should still be nominal with two out of three APUs.’
‘Could that be linked