Balky fuel system shuts down shuttle
NASA’s effort to return to space postponed as unexplained malfunction delays launch.
CAPE CANAVERAL, Fla. -- A persistent but unexplained fuel system malfunction has thwarted NASA's efforts to return space shuttles to flight.
Ground controllers in Florida called off the launch of space shuttle Discovery less than three hours ahead of its scheduled liftoff Wednesday, when a propellant level indicator on the shuttle's redesigned external fuel tank failed a preflight test.
"All I can say is, 'Shucks,' " Wayne Hale, deputy manager of the shuttle program and chairman of its mission management team, told reporters at the Kennedy Space Center.
The flight of Discovery to the International Space Station is to be the first by a shuttle since the Columbia re-entry disaster in February 2003. Liftoff now is scheduled to take place no earlier than Saturday.
As a result of the accident that killed seven astronauts, NASA spent the past two-and-a-half years improving heat shields on the winged orbiter and its fuel tank.
The sensor problem that halted Wednesday's countdown has vexed NASA engineers and fuel tank experts since April, when they tested the tank by filling it with 528,000 gallons of super-cold liquid hydrogen and oxygen. They got varying readings on whether the tank was full or empty. They got similar readings Wednesday, a few hours after Discovery's tank had been filled.
After the April failure, NASA tested the broken component and studied the problem for weeks. It even put off a plan to launch Discovery in May in order to swap out its fuel tank. Engineers were not able to determine what, if anything, was wrong.
Over objections of external tank project managers, shuttle program officials decided against a second fueling test with the new tank in June.
Orbiter project manager Steve Poulos said engineers suspect a faulty electrical circuit in the instrumentation that sends data from the fuel tank to the orbiter's onboard computers. The malfunction is a safety concern because the computers would use the data to help prevent accidental shutdowns of the shuttle's three main engines during the climb to space.
Wednesday night, technicians were draining the bullet-shaped tank with plans to test the sensor again when the tank is empty. They scheduled two meetings on Thursday to debate whether a Saturday launch attempt would be possible.
If that test reveals trouble with additional components in the fuel system, launch director Mike Leinbach said, it might be necessary to remove Discovery from its launch pad for repairs.
The sensor problem followed a Tuesday launch pad mishap in which a windshield cover fell and caused minor damage to the shuttle's heat shield. The damage was repaired. Hale said neither incident indicates that NASA is not ready to return shuttles to flight. "I think the safety process worked properly," he said. "It's a complicated vehicle with a lot of parts that have got to work right. We've built a very tight safety net to make sure we don't fly until it's safe."