Several Possible Causes Studied
Sunday, February 2, 2003
"Columbia, Houston, we see your tire pressure messages and we did not copy your last. . . . "
"Roger, buh . . . "
That was the final, broken exchange between flight controllers in Houston and Rick D. Husband, commander of the space shuttle Columbia, at the moment when, preliminary evidence indicates, the left wing came off.
The first indication of trouble arrived abruptly, shortly before 9 a.m. EST, when a series of sensor failures occurred in sequence from the trailing edge of the wing to the front. "It was as if someone just cut the wire," said an exhausted and distraught Ronald D. Dittemore, space shuttle program manager, in a briefing late yesterday.
The shuttle was passing through a period of peak heating at the time, with temperatures reaching 3,000 degrees on the leading edges of the wings.
Dittemore and other top NASA officials emphasized that no cause had been determined, and that the investigations -- three were announced yesterday -- are likely to take days or weeks. Possible causes include damage from foam insulation debris loosened during the launch, structural failure, catastrophic heating possibly after the loss of heat shield tiles, and a failure in the flight control system.
The U.S. Strategic Command in Omaha, which closely tracks space debris, said there were no signs that any foreign object had struck Columbia. But a spokesman stressed that the probe is only beginning.
A key to the cause of the disaster could come from the collection and reassembly of the shuttle debris, as in an airline crash, Dittemore said. Fragments of the spacecraft were spread over parts of at least two states -- Texas and Louisiana.
Considerable attention yesterday focused on a piece of foam insulation from the shuttle's large external fuel tank. The foam came loose and appeared to nick the protective tiles on the left wing during the launch. Columbia, the oldest in the shuttle fleet, lifted off from the Kennedy Space Center in Florida 15 days, 22 hours, 20 minutes and 22 seconds before the shuttle disappeared from NASA's telemetry.
Dittemore said earlier extensive analysis of the foam impact had indicated that it posed no threat to safety. He said there was no indication that hard metal, as opposed to foam, had detached from the tank.
It was the second time in the past three flights that a bit of errant insulation from the tank was detected in post-flight videos. In October, the shuttle Atlantis lost a piece of foam that struck the rear section of one of the two solid-fuel boosters. Analysis then indicated that no harm was done, and the flight proceeded.
Before yesterday's tragedy, flight managers had already made plans to take a closer look to determine whether these events were symptoms of a serious problem.