Posted on 04/01/2003 11:20:47 PM PST by HAL9000
Launch pad primer may have weakened Columbia's wing edges, enough to break when foam hit
A paint primer leaching off NASA's launch towers may have formed tiny holes in the leading edge of Columbia's left wing, weakening it enough to break when struck by a chunk of foam during liftoff, accident investigators said Tuesday.
Air Force Maj. Gen. John Barry said pinholes in the quarter-inch-thick protective carbon lining the wing may have allowed air pockets to form in the material. The air could have eaten away at the carbon like termites, a process called oxidation.
The holes have appeared on all four shuttles. NASA patched the larger holes, but did not check thoroughly for underlying air pockets, investigators said.
The accident investigation board is trying to determine what caused Columbia's destruction over Texas 1 1/2 months ago, an accident that killed all seven astronauts. The panel has focused from the start on the left wing, which was hit by debris during liftoff.
Pinholes were first discovered on Columbia in 1992, after 12 flights, and later appeared on the other shuttles, Barry said. As many as 20 to 40 pinholes formed on each carbon panel over the years, apparently the result of zinc leaching out of the paint primer on the metal tower that swings around the shuttle and protects it on each of the two seaside launch pads.
Because the aging structure was not repainted and refurbished, more primer was exposed and every time it rained, corrosive zinc oxide washed onto the shuttles, Barry said.
"This dates back to Apollo days, and a lot of that infrastructure has not been replaced because they had made a decision they were going to go" with follow-on spaceships, Barry said. "Infrastructure is definitely going to be part of our investigation."
Barry said NASA was aware of the leaching problem, but noted: "I don't think it quite got the attention maybe that is has now, obviously, with the mishap."
The board chairman, Harold Gehman Jr., a retired Navy admiral, said NASA addressed the problem of zinc oxide sprays by slathering the leading edges with sealant and other material.
"The question is, once again, just like everything at NASA. Who knew it high up? Was it a serious consideration? Did they have anybody looking aging as a weakening? We don't know that yet," Gehman said.
It's also possible that salt spray from the Atlantic formed the pinholes, Barry said.
The investigators also said they had found additional defects in a spare shuttle fuel tank, including a bonding problem with the insulating foam. In addition, they said the mystery object that floated away from Columbia while it was in orbit was almost certainly a metal support panel from the underside of the wing's leading edge.
The board's latest calculation on the size of the flyaway foam that slammed into the leading edge of Columbia's left wing 81 seconds after the January liftoff is 25 inches long, 15 inches wide and 5 inches thick. It weighed about 2 pounds and struck at 438 mph.
A 2-pound chunk of foam hitting a healthy shuttle, even on the vulnerable leading edge, probably could not hurt it, Gehman noted. But if it struck a ship "kind of worn and torn a little bit," catastrophic damage could result, he said.
Columbia was NASA's oldest shuttle and spent an accumulated 2 1/2 years on the launch pad.
The spare shuttle fuel tank being analyzed at the Michoud Assembly Facility in New Orleans, meanwhile, had 32 air pockets in the foam on the so-called bipod area, an attach point between the tank and shuttle, Barry said. This is where the foam broke off Columbia during liftoff.
Air pockets like these _ mostly 2 inches to 3 inches in size _ could cause the foam to pop off. Some foam in this location also was not bonded properly to the tank itself, Barry said.
"This was a big surprise to everybody," he said.
As for the mystery object that floated from Columbia just one day into its flight, it almost certainly was a so-called carrier panel, a 2- to 3-long strip of metal that connects the carbon panels on the leading edges to the thermal tiles that cover the rest of the wings. The Air Force Space Command detected the object via radar, but did not know it was there until after the Feb. 1 crash.
Right before the object was spotted, the shuttle performed a maneuver in orbit that probably shook it loose.
A single missing carrier panel would be enough to allow the hot deadly gases of atmospheric re-entry to penetrate and burn through the wing, said board member Roger Tetrault, a retired corporate executive who worked with nuclear submarines. But he said the breach in the leading edge of the left wing could also have involved the carbon panels, seals, stainless steel support structures or even bolts.
"We have to sort our way through all of those and make a determination of which one" failed, Tetrault said. "If we fail to do that properly and we get the wrong one, then we could have a future accident."
The carbon panel from the area where the board believes the breach occurred _ panel No. 6 _ was identified in wreckage at Kennedy Space Center in Florida on Tuesday. It appears to be intact and in good shape, which could prompt investigators to change their minds as to where the disastrous hole was located.
Thanks for the post.
Amazing, isn't it? All the billow and bluster about all these conspiracy plots that thundered all across Free Republic like a West Texas squall line may be just hot air and the real culprit is paint primer.
This from the folks who are supposed to be watching and warning NASA about space junk that is a threat to the spacecraft.
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