quote:
Entire banks of the orbiter's 44 jet thrusters, needed for precise maneuvers in space, must be shut off because of various malfunctions during most flights. In 1995, damaged thrusters aboard Discovery spewed hazardous fuel as it approached the Mir space station, much to the alarm of the Russians inside.
Electric arcing from damaged wire caused a shutdown of computers that controlled two of three main engines aboard Columbia in 1999. A backup system took over. But despite subsequent studies suggesting damage and deterioration of aging wiring, not all of it has been replaced.
NASA relies on exploding nuts and bolts to trigger the separation of the solid rocket boosters and external fuel tank from the shuttle. But devices designed to capture this pyrotechnic debris have repeatedly failed -- and possibly during Columbia's last flight -- raising the potential of chunks of metal ripping into the body of the shuttle.
At least one of the three auxiliary-power units, which provide hydraulic pressure needed to steer the orbiter, has had problems in most flights, usually because of overheating. Some have even caught fire during landing. NASA engineers were so worried that they commissioned in the late 1990s a major redesign of the power units -- but pulled the plug because of soaring costs.
NASA has been unable to prevent episodes of highly explosive hydrogen gas -- which leaks from the external tank, shuttle and ground systems -- accumulating beneath the shuttle as it sits on the launchpad. High concentrations of the gas have prompted several scrubbed launches.
posted 08-18-2003 11:30 AM
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