HOUSTON (AP) - After days of analysis, NASA backed away Wednesday from the theory that a piece of foam debris that struck Columbia during liftoff was the root cause of the shuttle disaster.
Ron Dittemore, manager of the shuttle program, said investigators now are focusing more closely on the desperate effort of Columbia's automatic control system to hold the speed of the spacecraft stable despite an increasing level of wind resistance, or drag, on the left wing. Dittemore said that after a careful study of the damage possible from the fall of a chunk of foam insulation that was believed to be 50 centimetres and one kilogram, investigators are "looking somewhere else."
"It doesn't make sense to us that a piece of debris could be the root cause of the loss of Columbia and its crew," Dittemore said. "There's got to be another reason."
He said investigators are now asking if there was "another event that escaped our attention" that might have caused Columbia to break up just minutes before the end of its 16-day mission, killing all seven astronauts.
Practically from the start, investigators have been looking at the possibility that the piece of foam that fell off the shuttle's big external fuel tank 81 seconds after lifoff Jan. 16 caused damage to the thermal tiles under the left wing that doomed the flight. The thermal tiles keep the ship from burning up during re-entry into Earth's atmosphere.
While Columbia was still aloft, NASA engineers analysed the potential damage to the thermal tiles and concluded that based on such factors as the estimated size, weight and trajectory of the chunk of foam, any damage to the tiles was minor and the crew was in no danger.
In recent days, some space experts have speculated that the chunk of foam was coated or infused with ice, which could have increased the weight - and destructive potential - of the piece that hit the shuttle.
"I don't think it's ice. I don't think there's an embedded ice question here," Dittemore said, adding that the foam is water-resistant and that an inspection team found no ice conditions that day. "So it is something else."
Dittemore said that during Columbia's final minutes, the autopilot was causing the craft to rapidly move the control surfaces and to eventually even fire small rockets in a losing effort to gain control of the yawing motion of Columbia.
Final bits of data from the spacecraft showed that "we were beginning to lose the battle," he said.
For this reason, Dittemore said his team is intensifying efforts to recover a final 32 seconds of data from the spacecraft.
This data, the very last signals from the dying Columbia, was not processed at Mission Control because the quality of the electronic signals was too poor to be considered reliable.
But Dittemore said the signals are being extracted from computers and will be examined to find clues to why Columbia's left wing was encountering so much drag.
"Perhaps the 32 seconds will help us understand," he said.
