Wing seal 'almost certainly caused shuttle disaster

Investigators probing the Columbia shuttle disaster say they are growing ever more certain that a damaged wing seal brought down the spacecraft, killing all seven astronauts on board.

A seal on the left wing was struck by foam during lift-off on February 1 and fell off the next day, creating a gap that let in enough scorching gases during re-entry to rip the ship apart.

The seal is now believed to be the mystery object that floated away in orbit and it was almost certainly struck by something – like a chunk of foam – before it came off, the accident investigators said.

“For 11 weeks, we have been saying that we don’t have any particular scenarios, any favourite scenarios,” said retired Navy Admiral Harold Gehman Jr, chairman of the investigation board.

“But I think 11 weeks into this, it’s time that we attempted to see where the evidence was pointing us.”

The board will meet Nasa officials later this week to begin reaching a hypothesis. The final report is not expected until mid-summer.

At their weekly news conference, the investigators also said numerous defects had been found in insulating foam on a fuel tank practically identical to the one on Columbia.

A chunk of the foam peeled away from Columbia’s fuel tank shortly after lift-off and slammed into the leading edge of the left wing, believed to be a key element of the disaster.

The investigators said the long, narrow gap from a broken or missing seal on the left wing probably expanded during Columbia’s descent two weeks later because of the intense heat of re-entry.

The resulting breach would have been large enough for atmospheric gases to burn their way through the wing and lead to the spaceship’s disintegration over Texas.

Navy Rear Adm Stephen Turcotte, a board member, said it was still too soon to say that was exactly what happened, but the evidence was pointing strongly in that direction.

“To say it was, in fact, a T-seal 100%, we suspect that,” Turcotte said. “I mean, we’re up there. We’re up there near the 70s and 80s per cent.”

Radar and other tests indicate a so-called T-seal was what was seen floating away from Columbia on its second day in orbit.

The object was not noticed during the flight but only in analyses after the accident.