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Wednesday, May 07, 2003
The Columbia shuttle disaster

I have not followed the discussions about the shuttle disaster as closely as I might have done. This BBC report suggests tests will be carried out to verify the theory that the breakaway piece of insulation alone caused the failure of leading edge seals. The report concludes thus:
The investigators will now carry out tests to see what happens when chunks of foam are fired at panels of reinforced carbon-carbon, or RCC, of the actual shuttle structure.

They will try to determine if the foam - weighing no more than 0.5 kilograms (one pound) but travelling at a speed of more than 720km/h (450m/h) - was enough to open the hole.
If this report is accurate, it appears that the test would be ignoring an important factor: the foam was insulation foam from the massive external fuel tank, not a random piece of foam. Only in complete isolation would it weigh as little as half a kilogram; it probably weighed substantially more.

Let me explain: the insulation was used to protect a tank of liquid hydrogen and liquid oxygen rocket fuel. This fuel would be at a very low temperature. According to this site, the oxygen is in the nose of the tank (temperature below -183 degrees Celsius) and the hydrogen in the tail (temperature below -253 degrees Celsius). There is an area between the two called the 'intertank'. This area may be warmer but it would still be cold. I wonder where exactly the insulation came from; it may make a big difference.

Most of the insulation would have been adjacent to a very cold tank. Under these circumstances, it is very likely that there would have been condensation, in the form of ice attached to or absorbed by the insulation. Given the size of the 'missile' that hit the wing, it is very probable that it weighed more than half a kilogram. A weight of one or two kilograms is not beyond the bounds of possibility.

Therefore, I do hope that when the tests are done, they take account of the possible effects of condensation.

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