Chicago Tribune

By sending an astronaut today to remove material dangling from the shuttle Discovery’s underbelly, NASA hopes to head off a safety threat that mission managers admit they do not fully understand.

In an agency known for its exhaustive planning of any new procedure, the unprecedented spacewalk raises a question:

Why attempt an untried remedy to address an unknown risk?

The answer lies in the wreckage of Challenger and Columbia, two shuttles destroyed in part because NASA and its contractors did not take poorly understood threats seriously enough. In each of those cases shuttle managers wound up demanding that engineers prove there was a problem – a deadly mistake, the Columbia accident board concluded.

“Operations must be proved safe, rather than the other way around,” the Columbia report said. “NASA inverted this burden of proof.”

That recent evidence of a “broken safety culture” seemed to be on shuttle deputy manager Wayne Hale’s mind this week as he explained why the repair would go forward. He said that even though engineers could not say precisely how the jutting material would affect the ship’s aerodynamics during re-entry into the atmosphere, there were enough worries to warrant action.

“This is kind of the new shuttle program, the new NASA,” Hale said. “If we cannot prove that it is safe, then we do not want to go there.”

The outcome of today’s spacewalk will be one measure of whether NASA has made needed improvements to its safety culture – or has simply become paralyzed from a surplus of caution.

Hale’s team spotted two thin pieces of ceramic-coated cloth, called gap fillers, sticking out between heat-resistant tiles on the shuttle’s underside, which experiences high temperatures during re-entry.

To fix the problem, astronaut Stephen Robinson first will try to pull out the material. If that fails he’ll turn to an improvised hacksaw made from an ordinary blade, plastic ties, Velcro and duct tape – a jury-rigged tool reminiscent of the on-the-fly techniques the Apollo 13 crew used to avert catastrophe during their 1970 mission.

NASA has allotted about six hours for the entire spacewalk this morning, and Robinson said he’ll need the time to do the job with care.

“It’s going to be like watching grass grow,” Robinson said during an interview from orbit with reporters. “Nothing’s going to happen fast.”

“I’ll have to be very, very careful,” said Robinson, who holds a Ph.D. in mechanical engineering. “But the task is extremely simple.”

The Discovery crew also took a call Tuesday from President Bush, who thanked them for being “risk takers for the sake of exploration.”

“Obviously, as you prepare to come back, a lot of Americans will be praying for a safe return,” Bush said.

Aerodynamics experts said NASA was right to take a close look at the gap fillers, even though one is sticking out just 1.1 inches and the other 0.9 inch.

When Columbia disintegrated over Texas in 2003, the mission team in Houston had less expertise on the intricacies of re-entry aerodynamics, experts said. Since then the agency has brought to the decision team engineers who know more about the physics of what happens when the shuttle begins its fiery, breakneck descent to the ground.

As the spacecraft re-enters the atmosphere at 18 times the speed of sound, air rushes past it in an unbroken stream that aerodynamics engineers call a laminar flow. When it reaches lower altitudes the flow becomes more turbulent. But studies have shown that even a slight protrusion like a gap filler can cause an early “boundary layer transition,” making the airflow more turbulent and possibly increasing heating on some parts of the ship by hundreds of degrees.

There’s little real chance that such a gap filler problem could result in loss of the shuttle and its crew, said Michael Holden, an aerodynamics engineer at Calspan University of Buffalo Research Center. But Holden, whose group was involved in NASA’s return to flight preparations, said the Columbia accident made the agency more sensitive to anything that could pose a threat during re-entry.

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“I think they’re being ultra-careful,” Holden said. “If these questions were posed years back, there probably wouldn’t have been anybody on the ground in Houston who’d know how to answer them. Now they have a team that’s the best in the business.”

The new vigilance is a calculated shift from the days of Columbia’s 2003 mission, when investigators found that “allegiance to hierarchy and procedure had replaced deference to NASA engineers’ technical expertise.” In contrast to the rigorous daily meetings during Discovery’s current mission, the Columbia board found that the earlier mission’s management team did not even meet on a regular schedule.

Discovery crew members said Tuesday that they thought the decision to make the spacewalk was sound, even though the gap filler likely would pose no threat to their safety.

In an interview before the launch of Discovery, Robinson said he tries to put all the risks of spaceflight in his California-bred perspective.

“I was foolhardy when I jumped off a mountain with my 40-foot hang glider when I was 15 years old, without a helmet,” Robinson said. “I know all about foolhardy, and this doesn’t qualify.”

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GRAPHIC (from KRT Graphics, 202-383-6064): 20050802 Shuttle repair

AP-NY-08-02-05 2128EDT