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However, the commentator's excitement-tinged announcement - ''We have ignition and liftoff of Columbia, reaching new heights for women and X-ray astronomy'' -masked a serious problem brewing in the Shuttle's main engines. It came to the attention of Collins and Ashby five seconds after leaving the pad, when they noted a voltage drop on one of their ship's electrical buses, which caused one of two backup controllers on two of the three engines to abruptly shut down. The third engine was unaffected by the glitch and, luckily, all three performed normally, propelling Columbia into a 246-km-high, 28.45-degree-inclination orbit.

Nonetheless, the scare was significant: on no other mission had a Shuttle crew come so close to having to perform a never-before-tried abort landing back at KSC. Had the primary controllers, which immediately took over, also quit, an engine failure was likely and that would have required Collins to wait for SRB separation, flip Columbia over, fly 'backwards' at more than 10 times the speed of sound in order to slow down and head back west, then jettison the ET and guide her ship down to the SLF in the darkness.

''We were prepared for that,'' she said later. ''We were listening for the engine-performance calls [from Mission Control] on ascent. This crew would have been ready to do whatever was needed.'' Columbia, luckily, was safely in space, but moving 4.5 m/s slower than expected; although that was an almost-imperceptible discrepancy, in view of her 28,000 km/h orbital velocity, it was enough for puzzled engineers to question whether there might have been a 1,800-kg shortfall in the 545,000 kg of liquid oxygen pumped into the External Tank before launch.

NASA confirmed on 24 July that the loading of propellants had been done properly, although that, in addition to the electrical short that knocked out the electrical bus, would become the subject of an investigation. ''Since it [the short] was very localised in its effect,'' said Randy Stone, NASA's director of mission operations, ''it could be a short at the main engine controller itself, but this is just speculation. Clearly, we must understand it before we fly again.'' High above Earth, although acknowledging the mishap, Collins downplayed it during a space-to-ground interview and praised her crew for handling it so well.

Analysis of still and video images taken during the launch also revealed another problem: what appeared to be a leakage of hydrogen gas from one of the main engines throughout most of Columbia's ascent. The images, particularly those from cameras mounted on Pad 39B, revealed a narrow, bright area inside the nozzle of the right-hand engine, possibly indicative of a weld-seam breach in one of more than 1,000 stainless steel hydrogen-circulation tubes. However, Wayne Hale, Columbia's mission operations director, was reluctant to comment on the cause of the leak, at least until the troublesome engine was back on Earth.

''Once we get the engine back,'' he told journalists, ''we will look at the nozzle and see if we really had a leak, then we will turn the metallurgists loose. It could be very simple and a quick fix or something that takes longer. I'm not sure I would call it a constraint to [future] flight yet.'' He suggested, however, that the leak might explain the otherwise-inexplicable 'missing' liquid oxygen: as hydrogen was lost at a rate of

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