CAPE CANAVERAL, Fla., Feb. 25 (UPI) -- NASA has recovered a heavily damaged piece of shuttle Columbia's thermal tile that apparently fell off before its total disintegration over eastern Texas, the panel investigating the fatal accident said Tuesday.
"We are now beginning to see some interesting trends and evidence in the debris," said Harold Gehman, head of the Columbia Accident Investigation Board.
At a news briefing Tuesday, Gehman unveiled two images of the charred and malformed tile, which was found in Powell, Texas, about 30 miles west of Fort Worth. The shuttle broke up near the Texas-Louisiana border on Feb. 1, killing seven astronauts.
A fragment of another tile located even farther west is en route to investigators, Gehman added.
The debris recovered from Powell shows the underside of the tile, which would have faced the orbiter's skin, worn away at the edges, probably from hot gases, Gehman said.
One of the leading theories of what happened to Columbia is hot plasma generated by the shuttle's high-speed plunge through the atmosphere got inside the ship's left wing through some sort of structural breach. Final minutes of flight telemetry show increasing drag on the shuttle's left side, sensor outages in the left wing area and high temperatures in the left wheel well compartment.
The top of the tile is heavily gouged, discolored and speckled with unexplained orange blotches.
"This is not typical of a re-entry tile. This is very unusual," said Gehman. "One of the riddles we have to sort out is whether this damage was done while the tile was still attached to the orbiter, or whether it was done after the breakup and that's what it looks like when you try to re-enter the atmosphere at 15,000 miles per hour in a non-aerodynamic state."
In addition to analyzing debris, the accident investigation board is developing computer models to try to account for the flow of hot gas inside the wing, timelines to explain sensor malfunctions and high temperature readings, and interpretations of video, photographic and telemetry of the shuttle's descent over the western United States.
"Accidents in complex systems often involve a chain of events," said Scott Hubbard, a NASA field center director who is serving on the investigation team.
Added Gehman, "We have six separate detective stories ... We're building a theory of how it could have happened thermodynamically, aerodynamically (etc.) It won't be proof, but it will be a convergence of possibilities."
The team also is scouring Columbia's launch processing records, its last maintenance and modification work as well as NASA and contractor management, safety, oversight, engineering and decision-making in hopes of uncovering not only the root cause of the Columbia disaster but contributing factors as well.
Gehman said the investigation still is in an early stage and therefore nothing has been ruled out. Among the hundreds of possibilities under consideration are whether orbital debris hit the shuttle, puncturing its wing; whether falling foam from the shuttle's external fuel during launch damaged the wing; and whether the shuttle's age was a factor in the accident.
The team also is assessing whether NASA paid proper attention to a series of studies and engineers' assessments warning of the shuttle's vulnerable thermal tiles and potential damage from debris hits during launch.
