WASHINGTON – In their strongest statement yet on the Columbia disaster (search), investigators said Tuesday that flyaway foam from the fuel tank was "the most probable cause" of the wing damage that brought down the space shuttle almost five months ago.
"We've been trying to line up all the Swiss cheese holes. I think those holes have lined up pretty good," said Roger Tetrault, a member of the Columbia Accident Investigation Board (search).
Tetrault said he believes the deadly breach was located part way down the leading edge of Columbia's left wing, at or near carbon panel No. 8. The engineering analysis as well as the shuttle wreckage pinpoints that location, he said. That is the spot -- or close to it -- where a 1-pound chunk of foam insulation from the external fuel tank struck during liftoff back in January.
"When you put all of those pieces of Swiss cheese together, it's a pretty compelling story that, in fact, the foam is the most probable cause of the shuttle accident," said Tetrault, a retired corporate executive who used to build nuclear submarines.
It was the first time any of the 13 board members, publicly at least, blamed the foam for the Feb. 1 disaster. All seven astronauts aboard were killed.
Also on Tuesday, NASA (search) released video and photographs of the crew salvaged from the 85,000 pounds of wreckage. They showed the five men and two women posing for official portraits, playing with objects in weightlessness and demonstrating daily routines like shaving and brushing teeth.
Now that they have determined the most probable cause of the disaster, the investigators are struggling with how best to express the finding in their final report, expected to be released by the end of July.
"The board will have to decide what word we want to use," said the board's chairman, retired Navy Adm. Harold Gehman Jr. "Do we want to say, 'We think it did, we're sure it did, it might of, we think most likely it did, the board is confident?'
"I have 13 different opinions on that and at some time I'm going to have to lock everybody in a room and come out with one set of words," he said.
Gehman expects to release an interim recommendation to NASA soon, possibly as early as this week, that will emphasize the need for caution to avoid damage to the wings' thermal protection shielding on every flight and to repair problems in orbit.
"The board is trying to craft words which will force NASA to do something," he said.
Gehman said half the final report will focus on NASA management and culture. The other half will involve technical matters, most notably the loss of foam from space shuttle external fuel tanks during every launch for the past 22 years.
NASA needs to stop flyaway foam as best it can, especially larger pieces, and toughen the shuttles' ability to endure these kinds of strikes because they probably will continue, Gehman said.
"It was designed not to, but that's now proven to be not the case," he said.
NASA should be able to resume shuttle flights in six to nine months, after correcting the most pressing problems, Gehman said.
Gehman said the board will not deal with the need for a crew-escape system, leaving that painful debate and decision to NASA. The commission that investigated the 1986 Challenger (search) explosion also did not make any recommendation regarding an escape pod or other redesign for improving astronauts' odds, he noted.
"We would have to do a complete study of how close the crew came to surviving and how long they lived and what they died from and all that kind of stuff, and we elected not to do that," Gehman said.
Tetrault said only two other possibilities, besides foam, exist for the disintegration of Columbia during its return to Earth.
"I can't eliminate micrometeorites, although I think the possibility of that is extremely small," he said. None of the sensors indicated a strike by space junk, he noted.
The only other possibility is a strike by a broken bolt or its housing during liftoff. Radar indicated a piece of debris flying away 126 seconds after the launch. It's possible the debris was part of one of the massive bolts that hold the boosters and external fuel tank together or the container that catches the bolt halves after they are explosively severed.
Again, an impact by a 40-pound piece of metal would have registered on the shuttle sensors, Tetrault said.
"Those are the only two that you can say has a possibility of the cause. There's nothing else that we know of," Tetrault said. "There are always unknown unknowns and you hope you're smart enough to have looked and found every one of those ... I certainly think that we've looked as hard as you can possibly can to find those."
Foam-impact tests by researchers in San Antonio should help confirm the board's leading theory, said Scott Hubbard, a NASA official serving on the board.
"The thing that I'm trying to do with these tests ... is to connect that dot from foam to breach," Hubbard said.