GRAHAM WARWICK / WASHINGTON DC
Investigators believe temperatures inside the Space Shuttle Columbia's left wheel well exceeded 1,650¡C (3,000¡F) as superheated air entered from a breach at or near the wing leading edge. Hot gas then sprayed out from the corners of the landing-gear door, depositing molten aluminium on the underside of the orbiter.
One of the recovered gear door uplocks shows evidence of melting. It is made of titanium, which melts at 1,650¡C. Hot gas may have entered the wheel well through a vent in the forward wall, but investigators say the plume could have burned through in seconds, saying that aluminium burns at high temperatures, adding to the heat.
One focus is possible damage to, and subsequent loss of, carrier panels fitted between the reinforced carbon-carbon (RCC) leading-edge panels and the underwing thermal-protection tiles. If a carrier panel were missing during re-entry, superheated air could have entered the wing behind the RCC and melted the metal fittings attaching the leading-edge panels. While one missing carrier panel is not a big enough breach to explain the temperatures seen inside the wing, it could have triggered the "unzipping" of a larger section of leading-edge RCC.
Columbia accident investigation board member Dr James Hallock says an object observed detaching from Columbia two days into its mission appears similar in size to a carrier panel. Tests are under way to characterise the object by its radar reflectivity. Insulation foam which separated from the external tank 82s after lift-off on 26 January is thought to have struck the underside of the left wing leading-edge in the region of the carrier panels. One theory is that the impact damaged or loosened a panel, which was then dislodged during in-orbit manoeuvres.
Source: Flight International
