Scientists Explore Metal's Burn Characteristics

The predominant component in the shuttle's structure, aluminum, can change under certain circumstances, becoming a fast-burning, explosive fuel of the sort used in armor-piercing munitions, bombs, and rocket boosters. That fact has led the Columbia Accident Investigation Board to inquire into the possibility that, as trouble mounted during Columbia's hot, violent re-entry, parts of its very frame might have ignited or even exploded.

Possibly Fueled Disaster?

If so, the burning aluminum may resolve what seems to be a contradiction that has troubled investigators from the start: Physical evidence indicates that destructive heat raced through the shuttle's left wing, but engineering calculations indicate that scenario could not have unfolded as fast as it evidently did. The explanation, said an official close to the investigation, may be that the aluminum alloy in the frame could have served as a kind of energy multiplier, accelerating the chain of disasterous events that eventually doomed Columbia and its crew.

"The more we learn about how aluminum behaves in these superheated temperatures, the better," said retired Admiral Harold Gehman, the board's chairman, at a news briefing this week. When aluminum gets superheated and turns into fuel, he said, it ceases to be a barrier. Instead, "this presents a new avenue for heat."

It Would Explain A Lot

The accident unfolded in a mysterious environment of hypersonic speeds and rarified atmosphere, in which aerodynamic forces, chemical reactions, and extreme heating interact in ways no on can yet predict. As specialists have told the board, there have been few opportunities, until now, to study what happens to spacecraft hardware when it barrels through the upper atmosphere and into the thicker layers of gas below.

The board, in recent days, has asked NASA's Ames Research Center in California to conduct experiments with aluminum "to get some laboratory data that we can hang our hats on," said an investigation official, speaking on condition of anonymity.

Columbia and its seven astronauts were lost on Feb. 1, probably because of damage to the leading edge of the shuttle's left wing that may have been inflicted by debris that sheered off the external tank during the Jan. 16 launch, investigators have said. Evidence from recovered wreckage and other sources indicates that, as the shuttle reentered the atmosphere, a breach allowed superheated air to blowtorch its way into the vulnerable aluminum behind the heat shielding and to flow through the inside of the wing, weakening it and eating into the main landing gear wheel well.

Analysts say no one has studied the properties of aluminum under the forces of reentry.

''You'd never build a reentry vehicle out of [naked] aluminum,'' said board member Sheila Widnall, an aerodynamicist at the Massachusetts Institute of Technology.

FMI: www.nasa.gov