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  sci-tech > space > story pagecorner  

NASA: Loose pin caused space shuttle hydrogen leak

shuttle launch
Engine leak at liftoff

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July 30, 1999
Web posted at: 12:21 p.m. EDT (1621 GMT)

From Space Correspondent Miles O'Brien

KENNEDY SPACE CENTER, Florida (CNN) -- NASA engineers probing the potentially hazardous hydrogen gas leak in the space shuttle Columbia's right main engine now believe they know what caused the problem -- and feel confident it will not be a show-stopper for the next shuttle launch, now scheduled for mid-September.

Several well-placed sources tell CNN a pin lodged into a tube that feeds liquid oxygen into the engine's combustion chamber -- at the top of the nozzle -- fell out, striking three 1,080 stainless steel cooling tubes ringing the nozzle bell the moment the engines started.

When the pin struck the cooling tubes it weakened them, eventually causing a rupture. Hydrogen leaking out of the holes caused the right main engine to run 100 degrees hotter and use more propellant. As a result, Columbia's main engines shut down about a second early, leaving spacecraft seven miles short of its intended orbit. The five-day mission was otherwise unaffected.

Had the leak been greater, it might have prompted the engine to heat to its so called "red-line" point, where it is designed to automatically shut down. That could have forced Commander Eileen Collins and her crew to fly a risky, and as yet untried, abort maneuver -- landing either in Africa or back at the Kennedy Space Center.

There are hundreds of tubes that deliver oxygen and hydrogen into the combustion chamber where the propellants are mixed with hydrogen and ignited. The tubes are inspected after every flight, and if there are any weaknesses or imperfections found, they are simply plugged with 8-inch gold-plated pins. Because there are so many of these tubes, this does not affect the performance of the engine.

Engineers discovered a pin was missing and found remnants of gold-plating near the holes in the cooling tubes leading them to this conclusion. It is unclear why this pin broke loose.

The engines installed on the next shuttle slated for launch -- Endeavour on September 16 -- do not have any pins in them, erasing any concerns of a recurrence of the problem then.

Still unresolved is the short circuit that occurred five seconds after liftoff, shutting down critical engine computers that control every aspect of performance on two engines. Each engine has a back-up controller, and they performed without interruption.

Ground crews were to begin troubleshooting the engine controller circuit Friday to see what might have caused the short.



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