Foam is still a suspect in shuttle probe

Engineers retrace the fateful descent

By Marcia Dunn, Associated Press, 2/7/2003

PACE CENTER, Houston -- A day after all but ruling it out as a leading cause, NASA said yesterday that investigators are still considering whether a piece of insulating foam that struck Columbia's left wing during liftoff was enough to bring down the shuttle.

Even though the possibility appeared remote, shuttle program manager Ron Dittemore said, investigators must remain open to every option as they put together a ''fault tree'' to assess the cause of Columbia's fiery breakup.

''The foam that shed off the [external fuel] tank is just one branch, and we are pursuing that, even though we scratch our heads,'' Dittemore said. ''We are going to pursue it until we pound it flat.''

NASA specialists are working backward through the shuttle's descent, starting at the moment communication cut out, in a search for even the tiniest detail that might explain the shuttle's destruction just minutes from its landing Saturday. Everything is being considered, from a freak meteorite hit to a landing-gear tire rupture.

Engineers taking part in the reverse analysis struggled yesterday to make sense of the eight minutes recorded between the first sign of trouble aboard Columbia, a surge in temperature in the left landing gear compartment as the shuttle passed over California, and the shuttle's final, dying moment over Texas.

Other engineers are taking a closer look at the temperature rise and the loss of sensors in Columbia's left wing and are trying to pinpoint the heat source.

Another team is focusing on the wind resistance, or drag, encountered by the left wing in the final minutes. They are trying to determine what loads would be required to cause the shuttle's steering jets to fire in a losing battle to gain control of the spacecraft.

NASA will be testing the impact of the insulating foam from shuttle fuel tanks on the thousands of fragile thermal tiles that cover each space shuttle. The Columbia's left wing was hit by foam 81 seconds after liftoff, though computer simulations have shown that the impact could not have been the only cause of the disaster.

On Monday, NASA officials said the foam was a ''leading candidate'' for the cause of the accident. On Wednesday, Dittemore all but discounted the theory that the foam was the ''root cause.''

Engineers also haven't written off the possibility that other debris during the Jan. 16 liftoff might have damaged Columbia.

Some specialists, both inside and outside the space agency, find it implausible that a 2 1/2-pound, 20-inch piece of foam could have caused catastrophic damage to Columbia. The debris smacked into the underside of the left wing, but engineers concluded during the 16-day flight that the damage would have been minor and posed no safety hazard.

''That's what everybody focused on; that's what you can see,'' said Steven Schneider, a professor of aeronautics and astronautics at Purdue University. ''But it's very commonly going to be not the thing which is so obvious. If it was so obvious, they would have figured it out. These people aren't stupid.''

James Oberg, a former shuttle flight controller who has written a number of books on the space program, said he is as baffled as everyone else.

Such catastrophes are seldom the result ''of a single stupid mistake or oversight, but are the multiplication of several factors,'' Oberg said.

Most of the debris field has been in East Texas and Louisiana, but Dittemore said that none of the shuttle parts considered crucial to their investigation had yet been found. He said reports of debris west of Texas, including in California, had not been confirmed as shuttle parts.

Meanwhile, in the nation's capital, Vice President Dick Cheney addressed a memorial service yesterday for the seven astronauts at the National Cathedral, where a stained glass window holds a piece of moon rock.

''They were soldiers and scientists and doctors and pilots, but above all they were explorers,'' Cheney said. ''They advanced human understanding by showing human courage.''

This story ran on page A2 of the Boston Globe on 2/7/2003.
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