[ATOMIC_PUNK]

Just out of curiosity, how do they know the tiles couldn't have been fixed in orbit

One explaination i heard is that theres no plan in place for repairing tiles in space another is that there is no foot or handholds on the bottom of the spacecraft because it would put to much heat to close to the shell of the craft upon reentry.

[mewzilla]

Sounds to me, then, like they didn't have a back-up plan for that eventuality anyway.

[Republic of Texas]

All the tiles are different. You would have to fill the payload with spare tiles. Not going to get much science done that way.

[txradioguy]

The curing process required to bond the tiles to the shuttle require that it be done in a process only capable of being done (at this time) here on earth. Each tile, from what I've read it individually shaped to fit that certain spot on the aircraft.