On Cnn they ran a little clip of videotape of it's last launching and they showed some sort of material coming off left wing. Conjecture is that part of debris from external fuel tank struck the underside of left wing causing some damage. It would be interesting to see if the length of mission,16 days, was extended beyond original schedule over some concern over what NASA saw in review of launch video.
What's more unbelievable in my mind is that pieces of the insulation and ice from the external tank regularly break off and strike the shuttle during launch. We just kept ignoring them. This time it was a particularly large piece that broke off judging from the video.
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