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Preserving shuttles terrific task



Submitted by Arthur - N1ORC
Previous permission granted by Houston Chronicle

Experts: Preserving shuttles terrific task
By ERIC PIANIN and KATHY SAWYER

http://www.chron.com/cs/CDA/ssistory.mpl/space/1906743


Outside experts suggest that safely maintaining the shuttles for many
more years may be a tougher challenge than NASA envisions, in part
because of new requirements the Columbia Accident Investigation Board
may place on the program, and in part because of disadvantages specific
to human spaceflight, such as reliance on a very small number of very
expensive vehicles. 

But there is another big factor, experts say. The entire aerospace
enterprise is going through the aging process for the first time in
history, which means there are a number of poorly understood aspects of
the problem and engineers are still being surprised by unexpected
effects from long-term stress on flying machines. 

"It's not like we can go back and find the predecessor of the B-52 and
see how it did in its 45th year. There isn't that data," said Robert
Ernst, head of the Navy's Aging Aircraft program at the Patuxent River
(Md.) Naval Air Systems Command. "There's no idiot light that just sits
there and goes, `Ding. Replace this aircraft and buy new aircraft.' " 

Too little is known about how aging affects wiring, composite materials,
pumps, motors and other components, according to Ernst and others.
Stress and strain may produce unexpected wear and tear, even more for
spacecraft than for aircraft. What seems certain is that the labor
demands and other problems soar with age. 

Even the venerable B-52s, so often cited by NASA as still going strong
when the Air Force's current version was rolled out in the 1960s, were
plagued by corrosion when based in Guam and other areas of Southeast
Asia. They were shifted to more benign environments and a policy of
"zero tolerance for corrosion" was instituted, said Jean Gebman, a
senior engineer at the Rand Corp. who has studied aging aircraft issues.
But the shuttle base is still perched at Cape Canaveral on the highly
corrosive , humid, salty Atlantic shore. 

When older aircraft are sacrificed in what is called a tear-down
inspection, technicians inevitably find previously hidden signs of
corrosion, he said -- as accident investigators have found in
inspections of shuttle parts. 

One of the advantages the aviation industry has over the shuttle program
is that it has flown huge numbers of vehicles a lot of times -- enough
to build a viable statistical database in at least some areas and enough
to sacrifice some craft to the inspections. 

The fact that the entire shuttle "fleet" is now down to three vehicles
severely limits the amount of prying, poking and shaking that engineers
can do on hardware. 

"If we had hundreds or even tens, we'd consider tearing down the older
ones. But when you're down to three, that's not an option," Gebman said.

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