The high-velocity impact of foam on the leading edge of a space shuttle wing causes serious damage, initial tests have revealed. The results were released by the Columbia Accident Investigation Board on Thursday.
The tests are the first direct assessment of a critical step in the sequence of events that CAIB believes is most likely to have caused the Columbia shuttle disaster. This is that insulating foam falling from the external fuel tank caused a breach in the leading edge of spacecraft鈥檚 left wing when it hit 81 seconds after launch.
Space shuttles have returned safely after foam impacts on thermal insulating tiles on the wing鈥檚 underside, but the leading edge is considered more critical because it must withstand extremely high temperatures during the shuttle鈥檚 return to Earth.
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The tests at the Southwest Research Institute in San Antonio, Texas, fired a 0.76 kilogram block of foam at the wing at 237 metres per second. The force of the impact lifted and moved the T-seal between two panels, opening a gap up to seven millimetres wide and 56 centimetres long.
Hot plasma
The results were consistent those predicted before the tests, CAIB reported. But, more importantly, the damage seen is very probably sufficient to have led to the loss of Columbia.
CAIB鈥檚 working hypothesis is that hot plasma penetrated a breach in the left wing caused by the foam impact as Columbia entered the upper atmosphere. The hot gas would have causing the wing to fail and Columbia to be destroyed. However, the board has yet to reach its final conclusions.
The wing used in the tests came from the shuttle Enterprise, which was used in early tests but is not rated for space flight. Other shuttle wings have leading edges made of reinforced carbon composite, which can withstand the high temperatures of reentry.
But NASA has few spare carbon composite panels, so CAIB used fibreglass panels in these first tests. Later tests will fire the panels against actual carbon panels that have been used on shuttles.