GRAHAM WARWICK / WASHINGTON DC
Early analysis suggests plasma entered left wheel well, but early gear deployment is thought unlikely
Investigators believe the Space Shuttle Columbia's thermal protection was breached during re-entry, allowing superheated gas, or plasma, into the wing. Preliminary analysis indicates temperature increases seen in the left wheel well would require the presence of plasma, says the Columbia Accident Investigation Board.
A missing tile would not cause the temperature indications seen in the last minutes of the 1 February flight, according to the NASA working group. Heat transfer through the exposed structure would not be sufficient to cause the 17°C (30°F) temperature rise recorded in the left wheel well before the break-up over Texas, killing all on board.
Various scenarios are being analysed in which a breach of some type would allow plasma into the wheel well area or elsewhere in the wing. But data does not support early deployment of the left gear, the board says. The scenario was suggested by a low-resolution ground telescope photograph of the re-entering Shuttle taken by the US Air Force, and supported by a sensor reading indicating the gear was down 26s before break-up.
"Other flight data including landing gear position indicators and drag information does not support the scenario of early deployment of the left gear," says the board. Two other sensors in the wheel well indicated the gear was still up and, although Columbia's flight control system was firing thrusters to counter increased drag on the left side, the drag was not enough to indicate the gear was down.
Last week searchers located a section of the Columbia's left wing reinforced carbon-carbon leading edge east of Fort Worth, Texas. As of late last week, no confirmed Shuttle debris had been located west of the city, although board chairman Hal Gehman says: "We have reason to believe that we should keep looking west of Fort Worth."
A "stereoscopic mosaic" of the Columbia's reentry is being assembled using more than 1,500 photographs and videos provided to NASA, most of which show ionisation around the Shuttle and not the orbiter itself, says Gehman.
Source: Flight International
