HOUSTON (AP) -- Columbia accident investigators said Tuesday that chunks of foam insulation broke off space shuttle fuel tanks more frequently than NASA realized and everything points to the debris as the cause of the disaster.
For two decades, NASA never considered the shedding foam a safety concern, even after a 2 1/2-pound section slammed into the edge of Columbia's left wing shortly after liftoff in January.
"We're going to tell them to fix the foam shedding, absolutely,'' retired Navy Adm. Harold Gehman Jr., chairman of the Columbia Accident Investigation Board, said at the panel's weekly briefing.
But he stressed that the group's final report, to be released this summer, will take a much broader view and look at such things as management practices, safety programs and the institutional culture at NASA.
During Tuesday's news briefing, Navy Rear Adm. Stephen Turcotte said he and others on the board have identified, by extensive film reviews, six previous shuttle flights in which foam peeled off the same part of the tank where it broke loose during Columbia's final liftoff. NASA had known about only four previous instances, he said.
Turcotte said the seven known instances are from 70 shuttle launches; no one will ever know whether the foam held during the 43 other liftoffs, because they occurred in darkness or the camera angles were bad. Foam flaking off from all over the tank left dozens of pockmarks each flight on the thermal tiles that cover much of the shuttle, Turcotte said.
The suitcase-size piece of foam that smashed into Columbia's wing was the biggest one yet, about twice the size of what came off during Atlantis' liftoff three months earlier and gouged one of the booster rockets.
In Columbia's case, ``I think that's what caused the breach,'' Turcotte said.
As part of the investigation, the board examined a fuel tank nearly identical to Columbia's and discovered numerous air pockets and other flaws in the same area where the foam broke off. Turcotte said dozens of defects were found that could have caused the foam to pop off during liftoff.
Investigators will take a closer look at how extreme cold and aerodynamic pressures affected the foam.
Turcotte said the board is looking into the way NASA came to accept these sorts of defects, over years and then decades.
"Over time, the foam has been falling off. It didn't hurt before. Wow, it hurt this time,'' he said.
The foam that covers the 154-foot tank is necessary to prevent ice from forming once the tank is filled with supercold fuel. The section of foam that broke off during Columbia's launch is sprayed on by hand; the rest is applied by machine.
NASA is proposing, among other things, to cover the foam at each so-called bipod ramp area, or tank attachment point, with a metal mailbox-type structure.
During the board's investigation, X-rays detected drops of molten nickel alloy on a fragment of a wing panel, indicating the probable area where the foam is believed to have hit, said another board member, physicist James Hallock, chief of the Transportation Department's aviation safety division.
Hallock said the breach in the wing could have begun as a narrow slit that widened as the shuttle went through the extreme heat of atmospheric re-entry. That would explain how the shuttle made it nearly all the way home before it disintegrated over Texas on Feb. 1.
"The comment we constantly keep saying to each other is, `Well, gee, this crack made it to eastern Texas. If we had an 8-inch hole out over the Pacific, I'm not sure we're going to make it to Texas,''' he said. ``So you have to have something that has to evolve with time.''
The 13-member board plans to move the bulk of its operation to Washington at the beginning of June and begin writing its final report. Gehman hopes to complete the report by the end of July.
Marshall Chief Leaving
Meanwhile, the head of the NASA center responsible for the space shuttle fuel tank that has come under suspicion in the Columbia disaster announced Tuesday that he is stepping down.
Arthur G. Stephenson, director of the Marshall Space Flight Center since 1998, said his departure was not connected to any problems at the center.
Stephenson, 60, will leave as Marshall director on June 15 and said he will assume an educational position within NASA until he retires in January. No immediate replacement was named.
The shuttle fleet is grounded as investigators try to pinpoint why Columbia disintegrated during re-entry on Feb. 1, killing all seven astronauts.
"With NASA preparing to implement a comprehensive 'Return to Flight' effort, I felt the timing for this move is in the best interest of the agency, Marshall and me, personally," Stephenson said in a statement.
Marshall, one of NASA's largest installations with more than 6,500 workers, oversees the shuttle's main engines, booster rockets and external tank.
Investigators suspect that foam insulation ripped away from the 154-foot tank during liftoff and damaged the shuttle's left wing, allowing hot gases to penetrate during re-entry.
In a February interview, Stephenson said engineers "got comfortable" with foam falling off during shuttle launches and never suspected the problem was a safety threat.
In 1986, Marshall director William Lucas retired after the Challenger disaster. Marshall was in charge of the flawed solid rocket booster that doomed Challenger during liftoff.
advertisement
