Word: foams
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Dates: during 2000-2009
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...came as a big relief early last week when NASA investigators determined that, yes, it was clearly a loose chunk of insulating foam that had damaged the shuttle Columbia's skin and led to its crack-up in the skies over Texas. Of course, they acknowledged, it was also possible that the ship actually started breaking up over California, and it might not have been foam that killed it, but a meteor. Or turbulence. Or an explosion in the wheel well. In fact, it began to seem that the only thing NASA could say with certainty was that nothing seemed...
Those investigations got under way even before the shuttle debris was cool. The most notorious piece of evidence was the bit of hardened foam that fell from the external fuel tank during lift-off, striking Columbia's left wing area. Applied like shaving cream, the foam dries to the hardness of a brick, which could conceivably damage the fragile external tiles that protect the shuttle during its fiery re-entry. When it was later disclosed that the spacecraft had spent 39 days idling on the pad before launch--enduring episodes of freezing rain that could have loosened the foam further...
...there were problems with the theory. First of all, the foam may seem as hard as a brick, but it isn't nearly as heavy. Even if the debris had been moving at 1,000 m.p.h. when it struck the shuttle's left side--about twice as fast as it was actually going--computer analyses suggested it could have done little damage. "It's difficult for us to believe...that this foam represented a safety issue," said shuttle program manager Ron Dittemore. That, at least, was the agency's position on Wednesday. On Thursday, however, NASA administrator Sean O'Keefe...
...foam was not behind the disaster, the wheel well might have been. Some of the flaky temperature readings that came down from the ship in its last few minutes originated in the left well, leading to fears that explosive bolts intended to help lower the wheel if it became stuck might have blown, damaging the ship. But the very purpose of the bolts is to detonate in the wheel space and do so safely. What's more, the well temperatures rose only about 40ºF in the last minutes of the flight, worrisome but not nearly high enough to trigger...
...With the foam and the bolts moving down the list of likely causes, a meteor hit moved up. Few people suggest that a cataclysmic collision simply blew the ship out of the sky--not so low in the atmosphere, anyway. But up in orbit, a bad ding by a rogue rock could have done enough damage to cause serious drag as the ship descended through the atmosphere, and Columbia indeed heeled sharply to the left before it disintegrated. Pits and gouges in the protective tiles are common during flight; ships routinely pick up close to 100 of them...