It 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 to be certain at all.
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