[WhirlwindAttack]

My first thought, regrettably is sabotage.

I just said the same thing to my wife.

[eno_]

The only "evidence" for sabotage is that the shuttle is a highly visible and symbolically significant target. But against that there is the fact that there was a massive security program in place to avert this.

Plus, there is a consistent alternative explanation: If the wing was damaged enough to cause a problem, that problem would have manifested itself on re-entry.

And add to that the fact there are many highly effective terrorist attacks that would have a much larger casualty and economic impact on the U.S.