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Panel May Urge Extensive Tests for Shuttles
APE CANAVERAL, Fla., March 26 — The independent board investigating the Columbia disaster is concerned that NASA may not be detecting flaws on the panels that protect the shuttle wings on re-entry and will recommend extensive new tests before further flights, an investigator close to the panel said today.
The Columbia may have lifted off with pre-existing flaws that simple visual inspections and a "tap test" could not detect, the investigator said in an interview. More sophisticated tests on panels from surviving shuttles have found flaws that the investigator said made them unsafe for flight.
One question before the panel is whether debris that hit the Columbia shortly after liftoff struck an already flawed panel.
The U-shaped panels that protect the leading edges of the wings are made of a multilayered composite material, reinforced carbon-carbon. Flaws in manufacturing, strikes by micrometeorites or mishandling can create gaps between the layers, cracks or other problems. Some experts said they believed that the Columbia, struck by debris 82 seconds after liftoff, might have entered orbit with fatal damage to such a panel, but that the problem might have been more than just debris.
"There's an argument that strong R.C.C. panel could have withstood a foam impact," an investigator said.
At a briefing here, the chairman of the commission, Adm. Harold W. Gehman Jr., who is retired, said today that his group was close to issuing two recommendations. He confirmed only that one concerned taking pictures of the shuttle in orbit to search for damage.
The investigators close to the panel said that recommendation would call for using "classified assets," a code term for spy satellites. Because the images would display the abilities of the satellites, using the satellites may require some NASA officials to receive security clearances.
Today, board members showed a carbon panel from the Enterprise, a test
vehicle at the Smithsonian that was hauled to high altitude by a
Experts pointed out that since the shuttle first flew more than 20 years ago, other industries have vastly improved the technology of "nondestructive examination." Those techniques include X-ray and ultrasonic probes, heating composite panels and watching how the heat is absorbed. That can be a clue to how well the layers are bonded together.
A spokesman for NASA, Bruce Buckingham, said technicians went beyond visual inspections and tap tests only in major overhauls.
"That's the way we've been doing it for 20 years," Mr. Buckingham said.
The investigators said they continued to be far from reaching a conclusion about the cause of the accident on Feb. 1 but were making progress. In a news briefing here, one panel member, G. Scott Hubbard, said this afternoon that a new analysis showed that the area of the orbiter most likely hit by debris included three carbon panels where the wing begins to curve out from the fuselage, as well as adjoining tile-covered panels. The highly likely area may have included tile on the underside of the shuttle.
Those findings are important, because when the space agency realized soon after the launching that the debris had hit the shuttle, it ordered an analysis. But the subcontractor that did the work, Boeing, used a computer model that estimated damage to the tiles, not the leading-edge panel.
Also today, NASA wreckage experts said that they had completed searching two-thirds of the main debris area, four miles wide and 250 miles long, and that they hoped to finish in four to six weeks. By then, spring foliage will make searching much harder, they added.
The Kennedy Space Center has received 54,000 pounds of debris, 24 percent of the orbiter's dry weight of 223,000 pounds, and debris continues to arrive, at the rate of two truckloads a week.
How much more is recoverable is not clear. The shuttle test director at the space center, Steven Altemus, said 35 percent to 50 percent of the shuttle returned to Earth's surface, with the remainder burning up on the way down.
"We see molten aluminum on almost everything we have back," Mr. Altemus said, adding that the surviving parts appear to have passed through "an aluminum molten rain cloud."
Many are too small to identify, he added, although NASA is using a computer program to try to match together jagged edges like a three-dimensional jigsaw puzzle. But some edges were burned away on re-entry.
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