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Determining what went wrong
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| 03 February 2003 |
By Phillip S Clark
At
present it is only possible to guess what went wrong with the re-entry of
Columbia – and there is no promise that any of the guesses will turn out
to be accurate. After its launch NASA noticed that some debris from the shuttle’s orange External Tank broke off and hit the left wing of the orbiter, and therefore it is natural to link that with the orbiter’s destruction. While in orbit, however, the crew showed no signs of worry about re-entry.
It is possible that the debris could have damaged some of the tiles that form the orbiter’s thermal protection system, but that system is designed not to catastrophically fail if a few tiles are lost. Orbiters have lost tiles in the past and, while the exposed areas have been ‘hot spots’ during re-entry, there has been no indication that a major failure was imminent.
If some tiles around the landing gear storage area had been damaged then this could account for the increase in temperature and pressure in that area. The tyres could have simply expanded and then exploded, destroying the aerodynamic integrity of the left-hand wing.
It is possible that debris hitting the left wing following launch is a complete coincidence, but this cannot be ruled out at present.
What destroyed Columbia seems to have been centred on the left wing. It is possible that the seals of the wing’s aerodynamic flaps had been damaged or lost. This would have resulted in hot gases flowing between the wing and the moveable flap, causing increased temperatures on the wing and subsequently the loss of aerodynamic control of the orbiter.
What we appear to see from the video of the orbiter’s re-entry is not a major explosion of the vehicle but the aerodynamic break-up of the vehicle as it started to fly well outside its design envelope.
Whatever the final catastrophe was, it was certainly sudden because the crew apparently noticed nothing wrong until the sensor warnings immediately before the loss of signal with the orbiter.
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| Columbia takes off on mission STS-107 on 16 January. Initial investigations into its break-up upon re-entry have looked at damage that may have occurred on take-off (Photo: Tom Rogers) |