Investigators - Slit on wing may have doomed Columbia

HOUSTON -- A long, narrow slit on Columbia's left wing may have let in scorching heat and doomed the space shuttle during its plunge through the atmosphere, accident investigators said Tuesday.

A slit possibly caused by a missing or broken seal on the leading edge of the wing is the latest -- and now strongest -- suspect in the 2 1/2-month-old inquiry.

The seal is close to where the investigators believe a chunk of foam insulation hit during liftoff, and the impact could have broken or weakened the seal and all or part of it floated away from Columbia during its second day in orbit.

"It's possible we may not be dealing with a round hole but instead something that created a long, narrow slit," said Scott Hubbard, a high-ranking NASA official on the Columbia Accident Investigation Board.

The board previously suspected that a mysterious object seen floating away from the shuttle was another part of the wing. But additional testing and the growing debris collection have ruled out a so-called carrier panel, and the only remaining possibilities are a seal or a fragment of a reinforced carbon-fiber panel, said Navy Rear Adm. Stephen Turcotte, a board member.

The U-shaped carbon-fiber seals are located between each carbon panel and wrapped around the leading edge of each shuttle wing.

These custom-fitted seals, like the carbon panels, are bolted onto the wing and subject to wear and tear. If even just one bolt was damaged by the foam that broke off Columbia's fuel tank barely a minute after liftoff, the seal or a chunk of it could have come loose the following day, the board said.

The board doesn't yet know the size of the breach.

The mystery object was not noticed during the shuttle flight. The Air Force Space Command discovered it in its radar-tracking files only after the spaceship disintegrated over Texas on Feb. 1, killing all seven astronauts. The object re-entered the atmosphere and burned up a few days later.

During their weekly news conference, the investigators announced their revised calculations for where the foam struck 81 seconds into Columbia's flight -- a little farther outboard on the leading edge of the left wing. This new "strike zone" is based on camera views of the tumbling debris that are constantly being refined, Hubbard said.

Other evidence seems to bear out the new targeted location. Tape from a salvaged data recorder shows a temperature spike in this location eight minutes after Columbia entered the atmosphere.

"This baby went up 350 degrees in about two seconds," Gehman said.

In addition, unusual and extreme heat damage has been found on two wing panels recovered from this same area. The panels were eroded in places like the edge of a knife, down to the thickness of a dime, Hubbard said.

Gehman stressed that he's not frustrated by the revised calculations or that the board is running out of prime suspects.

"We have always allowed for the possibility that we can't prove the guilty party," he said. Even if that happens, "there's still no doubt that heat got in there some way and there's still no doubt that we have a case of aging orbiters which have not been properly measured."

Gehman said he will release the first set of interim recommendations for NASA this week. The board will urge NASA to adopt better methods for testing wing panels, seals and other shuttle parts for age-related damage and routinely photograph orbiting ships for possible damage. The space agency already has requested such observations from the military.

The massive search for shuttle wreckage in East Texas, meanwhile, should be completed by the end of April, Gehman said. So far, about 36 percent of Columbia has been found.