NASA’s Tests May Add Look inside Shuttle Wings
HOUSTON — NASA needs to go beyond its current visual inspections of space shuttle wings between flights, making use of high-tech tools to peer inside them for tiny flaws, according to the board investigating the Columbia disaster.
In the next week, the Columbia Accident Investigation Board is expected to give the National Aeronautics and Space Administration its first two recommendations to put in place before flying again:
Use more sophisticated tools to examine the reinforced carbon-carbon panels that cover the edges of the shuttle’s wings. Possibilities include anything from CT scans to sound waves to lasers.
Get satellite imagery of the space shuttles in orbit so they can be studied for potential damage during launch. NASA already has agreed to this, after failing to get such photos for Columbia, which was struck during launch by a large piece of foam that broke off the ship’s external fuel tank.
The board suspects that the debris damaged the edge of the orbiter’s wing, causing a breach that allowed hot gases to get inside during the ship’s re-entry through the atmosphere. Seven astronauts were killed in the Feb. 1 accident.
The debris incident was caught on video, which shows the foam struck the left wing close to Columbia’s fuselage. But new questions have emerged about what may have been damaged.
During Columbia’s second day in orbit, ground radar picked up an object that is thought to be a piece of the wing floating away from the spaceship.
The mystery object re-entered the atmosphere, where it presumably burned up. Investigators think it may have been a so-called carrier panel — a segment that connects the leading edge to the rest of the wing — which had been knocked loose by the debris strike.
However, searchers in Texas have found pieces from carrier panels or the insulating tiles that go on top of them from those segments closest to the shuttle’s fuselage.
As a result, though a carrier panel hasn’t been ruled out, a board spokesman said more testing is being done to see if some other wing segment might actually have come loose.
For example, “we’re just having to go back and make sure that it wasn’t a piece of the reinforced carbon-carbon panel that had broken off,” said Lt. Col. Tyrone Woodyard, a spokesman for the board.
The board’s recommendation for better evaluation of the wings’ leading edge is prompted by the suspicion that the carbon panels could have been more vulnerable to damage because of undetected pinholes and aging.
Most of Columbia’s panels were original equipment and nearly 22 years old.
The reinforced carbon-carbon panels are large, U-shaped structures that wrap around the edge of the wing and are coated with a quarter-inch of special carbon insulator. There are 22 panels on each wing, providing protection for temperatures that can reach up to 2,300 degrees Fahrenheit.
NASA has found pinholes in the past, and board members say the damage may be caused by zinc that leaches off unpainted parts of the shuttle’s launch complex and eats away at the carbon panels.
Investigators say the pinholes can broaden into tiny tunnels below the surface of the panel.
Board chairman Harold Gehman Jr. likens the problem to “termites” that end up weakening the structure overall.
“If NASA doesn’t know the condition of its vehicles, we would be leery of recommending that they fly,” said Gehman, a retired Navy admiral. “Some of these things might be pretty simple, you know, a CAT scan of the leading edge. You can do it in place; you don’t have to remove it. If it passes, you’re good to go.”
NASA currently inspects the panels visually between flights, using up to 20 times magnification when suspected trouble spots are discovered, said James Hartsfield, a NASA spokesman at Johnson Space Center.
When serious damage is suspected, the panels are removed and sent back to the manufacturer, where ultrasound and CT scans can be used for analysis, Hartsfield said.
The board’s recommendation would make those techniques routine. Ultrasound — which employs high-frequency sound waves — is used routinely in the airline industry to examine composite materials that are similar to the shuttle’s reinforced carbon-carbon.
“Actually, I’m kind of surprised that NASA doesn’t do this already,” said Bill Waldock, a professor of aviation safety science at Embry-Riddle Aeronautical University’s campus in Arizona. “Particularly with composite structures, you can’t really see subtle damage with visual inspection. Sound waves lets you inside the internal weave of the structure itself.”
The recommendation that NASA seek satellite imagery of the shuttle comes after Columbia’s managers overruled a request by engineers, who said they needed more information about possible damage to the orbiter.
Last month, NASA Administrator Sean O’Keefe announced an agreement with the National Imagery and Mapping Agency to routinely get images from spy satellites.
O’Keefe said he’d negotiate a similar agreement with the Air Force, which has high-powered ground-based telescopes. But pictures taken of Columbia by a military telescope in Maui and posted on a NASA Web site are too grainy and fuzzy to show much detail.
Meanwhile, the board may begin writing its final report as early as mid-May and will release its final set of recommendations before the end of summer.
When the writing starts, the board likely will move its base from Houston to Washington, D.C.
However, the report and the remaining public hearings may not include testimony from many key witnesses in the investigation, such as shuttle senior managers and engineers.
The board has promised dozens of witnesses confidentiality in an effort to get more candid responses — meaning that the public never will hear much of the investigation’s most important testimony.
“By granting people privilege, we’re going to find things out that they wouldn’t say in public,” Gehman said. “And so we believe we’ll actually be able to go deep and get a richer and more fundamental understanding of these processes than you can in public.”
By Robyn Suriano and Michael Cabbage
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