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Shuttle breached 3 times before Original Source Link: (May no longer be active)
http://www.floridatoday.com/columbia/columbiastory2A5346A.htmhttp://www.floridatoday.com/columbia/columbiastory2A5346A.htm
Jul 8, 10:51 PM
Wings breached 3 times
Hot gases penetrated orbiters before shuttle tragedy
By John Kelly and Todd Halvorson
FLORIDA TODAY
CAPE CANAVERAL -- Superhot gases burned through shuttle wings on at least three missions before the Feb. 1 loss of Columbia, causing significant but less severe damage to orbiters, internal NASA documents show.
What's more, the shuttle's composite carbon wing panels -- which protect the ships and astronauts from intense heat encountered during atmospheric re-entry -- were damaged but not breached on at least nine additional missions, records show.
NASA already is launching an effort to gauge the integrity of its reinforced carbon carbon panels, which serve as thermal armor for the front edge of shuttle wings.
The agency also will use more high-tech means for inspecting the $800,000 panels, such as ultrasonic and electric current examinations.
Both endeavors are being carried out in response to a recommendation from the Columbia Accident Investigation Board. Both are to be completed before NASA returns it's remaining three shuttles to flight.
"There are teams that are evaluating all aspects of the vehicle to posture us to return to flight as soon and safely as possible," said Kyle Herring, a spokesman for NASA's Johnson Space Center in Houston. "We're going do everything we can, obviously, to do those kinds of inspections to ensure that the vehicle is safe."
One of the panels on Columbia's left wing was struck by a 1.7-pound piece of foam insulation that broke free from the shuttle's 15-story external tank 81 seconds after a Jan. 16 launch.
Accident investigators say the debris strike damaged the panel so badly that hot gases penetrated the wing during atmospheric re-entry, causing the ship to disintegrate over East Texas.
All seven astronauts aboard were killed.
A Florida Today review of mission and runway inspection reports as well as separate NASA problem reports, many of which the newspaper obtained under the Freedom of Information Act, showed that damage to the leading edge of the shuttles' wings is not uncommon or new.
The three previous breaches are significant.
The composite carbon panels encounter temperatures as high as 3,000 degrees Fahrenheit during atmospheric re-entry. A penetration of hot gases, consequently, can lead to the loss of a $2 billion shuttle and its astronaut crew.
The problem dates back to the early days of the shuttle program.
On NASA's second shuttle flight in November 1981, hot gases blasted past Columbia's wing panels near a spot where they join with heat-shield tiles on the underside of the orbiter, according to a mission report.
The searing heat scorched and burned through a fiber barrier used to fill gaps between heat-shield components. The gases streaked an aluminum spar inside one of wing, the report says.
NASA subsequently modified the thermal barrier and saw less damage on the next flight.
A similar problem, however, cropped up again on NASA's fifth shuttle flight in November 1982 -- another Columbia mission.
A jet of hot gas melted a small hole in a tile-covered metal bar connected to a wing panel. It damaged internal insulation but none of the metal components inside the wing, a mission report says.
No damage was noted on the next flight.
A more recent incident came at the end of a May 2000 Atlantis mission to the International Space Station. On that flight, hot gases penetrated a dislodged seal between two panels on the shuttle's left wing.
A subsequent investigation showed the seal had been installed improperly during a shuttle overhaul, creating a quarter-inch gap that served as a "substantial flow path" for hot gases, a NASA document says.
Charred and scorched as a result: Internal components made of Inconel and titanium – metals that have melting points between 2,500 and 3,000 degrees, respectively.
The damage was repaired and NASA ordered changes in the way that seals between wing panels are installed.
Less threatening but still significant damage has been more common.
Micrometeoroids and launch debris strikes dented or cracked wing panels on at least nine missions between April 1991 and March 2001, NASA records show.
Wing panels also have been damaged by exposure to extreme temperatures and pressures encountered during flight. And zinc primer leaching off the launch tower has corroded them.
The lesser damage has ranged from small pits to larger cracks.
Investigators have raised concerns about whether the panels weaken with age too. Only three of Columbia's panels were replaced during its 22 years of flight.
Investigators, meanwhile, think even a relatively small crack in a wing panel could doom a shuttle crew. The damage done to Columbia, however, likely was more dramatic.
In a test Monday, a 1.7-pound chunk of foam blasted a 16-inch hole in a shuttle wing panel. Investigators say the experiment at San Antonio's Southwest Research Institute was the most realistic simulation of the debris hit that downed Columbia.
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