The U.S. space agency NASA will investigate the possibility that foam debris damaged the shuttle Columbia's wing during launch, although it says it still considers it an unlikely cause of the orbiter's disintegration Saturday. As search teams continue the hunt for debris, an independent board has taken control of the investigation from NASA.
To learn why Columbia broke apart before landing, NASA technicians are investigating every possible cause, no matter how unlikely.
They have all but ruled out one cause - a piece of insulating foam that broke away from the shuttle's external fuel tank and struck its wing during liftoff.
But shuttle manager Ron Dittemore says engineers will conduct tests anyway to see if it could possibly have damaged the wing's insulating tiles enough to make it vulnerable to the searing heat of atmospheric re-entry.
"So even though I mentioned to you I thought it was not one of the primary items in our mind, we are pursuing it with great effort," he said. "No possibility is being ruled out. We are still looking for that elusive missing link."
Mr. Dittemore says NASA technicians are checking all evidence submitted by the public, including photographs that appear to show lightening striking the shuttle. Other theories being considered range from a hit by space debris to an exploding tire in the shuttle's left landing gear.
The only thing NASA knows for sure is that sensors from Columbia's left wheel area and left body sent back data showing an unusual rise in temperature just minutes before mission control lost contact with the orbiter.
In east Texas, rainy weather is hampering the hunt for debris in the area where most shuttle parts are concentrated. Search teams are trudging through muddy fields and forests.
News reports say 12,000 shuttle parts have been found, but only 1,000 have arrived so far at Barksdale Air Force Base in Louisiana. Mr. Dittemore says all available pieces will eventually be reassembled back at the Kennedy Space Center launch site in Florida.
"We will collect the debris in the immediate term up at Barksdale Air Force Base," he said. "It will basically be laid out on the floor for viewing and inspection. It is our intent to transfer the articles to the Kennedy Space Center and reconstruct the vehicle the best we can at the Kennedy Space Center so that we learn more about the accident."
NASA has turned over control of the investigation to an independent board of experts. The panel is headed by retired U.S. Navy Admiral Harold Gehman, who led the probe into the October, 2000 terrorist attack on a U.S. destroyer in the Gulf of Oman.
The board's mandate to investigate comes from a charter NASA put into effect after the shuttle Challenger blew up in 1986. NASA faced accusations at the time that it was secretive about the Challenger probe and rewrote its accident investigating rules.
NASA administrator Sean O'Keefe appointed Admiral Gehman, but vows that the agency will not interfere with his panel's work or the conclusions its draws based on the accident evidence. Mr. O'Keefe says that at the board's request, its charter has been rewritten to strengthen its independence from NASA.
"This is to absolutely guarantee that we have eliminated any ambiguity as to the independence of this board," he said. "We really want to be sure that we are not eliminating any set of possibilities of what could have contributed to this accident."
Next week, the U.S. Congress will begins its own independent probe of the shuttle disaster. The Senate and House of Representative committees that oversee NASA will hold a rare joint hearing on Wednesday.