re: shuttle backup plan question.
Personally I don't think there's much chance of a duplication of what happened to Columbia. If the shuttle has another catastrophic failure it will probably be for another as yet un-detected flaw. The horrible thought has often occurred to me that it's failed on launch, and failed on re-entry, so the next thing would be something bad go wrong while on orbit. Enough depressing pessimism, let's go ahead and launch a few times with a backup if that makes them feel better.