Sources close to the accident board indicated that the heat in the leading-edge idea was now a “leading theory.” No debris from the shuttle has yet been found west of Texas. But a source close to the investigation suggests that other evidence has begun to convince experts that some debris began “exiting” the shuttle “much earlier,” when the craft was still over the Far Western United States. The accident board will hold a public hearing this week at which experts will discuss how debris from space behaves when it re-enters the atmosphere.
A NASA spokeswoman said the space agency’s engineers were unaware of major historical problems with in-flight damage to the panels that protect the wings from the heat of re-entry. “This is not something we routinely encounter,” the spokeswoman said. But a government source said that some NASA engineers acknowledge that serious damage to the leading edge’s thermal protection panels could pose catastrophic risks for a shuttle on re-entry. While the reinforced carbon-carbon material, a kind of hyper sophisticated plastic used to protect wing edges during re-entry heat, is said to be far more durable than the fragile thermal tiles used to protect the wings’ undersides, experts say that a lot is not known about how the material performs under certain conditions, including old age. (The Columbia was the oldest shuttle in NASA’s fleet.) Investigators still aren’t ruling out the possibility that damage to the leading edge of Columbia’s left wing was caused by debris from the shuttle’s fuel tank which hit the wing during takeoff. Other possible causes of damage, such as a collision with “space junk” or wear and tear which could have caused pinhole perforations of leading-edge panels, are also being explored.
