Air pockets in foam puzzle shuttle board
© St. Petersburg Times
CAPE CANAVERAL -- Accident investigators said Wednesday they found air pockets in the insulating foam of a spare shuttle fuel tank, potentially treacherous flaws that may have been present on the tank that shed debris during Columbia's final liftoff two months ago.
"We found some voids that shouldn't be there," said Navy Rear Adm. Stephen Turcotte, an investigation board member. "Was that the smoking gun? We don't know."
Turcotte said the board does not yet know what caused the small air pockets in the foam of the tank dissected last week at Michoud Assembly Facility in New Orleans. The tank was a little newer than the one on Columbia.
"We're looking at the processes that were used, obviously, and when they were done and what propellants were used to spray it -- all of those factors," he said.
As they wrapped up a second day of public hearings on the disaster, the investigators also said the data recorder discovered last week in Texas may hold "a gold mine of information" that could help determine what destroyed the shuttle Feb. 1, killing all seven astronauts.
"The million-dollar question, of course, is what's on it," said NASA's Scott Hubbard, a board member.
Much of the investigation has focused on what happened during Columbia's liftoff Jan. 16.
A big chunk of foam, possibly with ice or other material attached, broke off the so-called bipod ramp area of Columbia's external fuel tank a minute after liftoff and slammed at 500 mph into two and possibly three or more heat-protective carbon panels on the leading edge of the left wing.
Almost all of the carbon panels on Columbia, NASA's oldest shuttle, were original and may have deteriorated over time because of wear and tear, the board said. The board's chairman, retired Navy Adm. Harold Gehman Jr., said one astronaut told him Columbia spent 21/2 years on its seaside launch pad over the past two decades, suggesting the metal bolts used to hold the wing panels in place may have corroded.
The board released a new "footprint" pinpointing the impact area on the wing. Resembling a pork chop, it includes three carbon panels on the leading edge, underlying support strips as well as some of the thermal tiles on the bottom of the wing, close to the left landing gear compartment.
The footprint is not exactly the location identified by engineers while Columbia was still in orbit, said Hubbard, the lone NASA representative on the board. Those same engineers concluded that any damage to the wing was minimal and posed no safety threat.
"I think everybody was in the same ballpark, but we may have been in adjoining sections," Hubbard said.
"It would be unfair to say we know 'X' marks the spot," he added. " 'X' in this case is an area two or three feet in diameter."
Hubbard pointed out that it took almost two months for experts to pinpoint the area of impact. The in-flight analysis by Boeing, which dismissed all safety concerns, lasted about one week and was just that -- an analysis involving no impact testing.
What's more, the computer model used in the Boeing assessment did not account for damage to the carbon panels that cover the leading edges of the wings, Hubbard said.
High-speed impact testing will begin in two weeks in Texas on actual shuttle pieces. One- to two-pound chunks of foam will be hurled from a giant nitrogen-pressured gas gun at carbon panels, thermal tiles and carrier panels to gauge the amount of damage. The foam chunks will measure about 24 inches long and weigh one to two pounds, the calculated size of debris that fell off Columbia's fuel tank back in 1992.
As for the data recorder, the 9,400 feet of salvaged magnetic tape has 15 inches' worth that is crumpled and wrinkled, but investigators are hopeful data can be retrieved from the rest of the reel, Hubbard said. NASA plans to duplicate the tape in the next day or so and send the dub to Johnson Space Center in Houston for analysis.
The recorder was collecting temperature, pressure, vibration and other data from 721 sensors on Columbia's wings, fuselage and tail. It's unlikely, though possible, that the recorder registered the impact of fuel-tank foam on Columbia's left wing during liftoff, Hubbard said.
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