[Jesse]

I was thinking about that. While the velocity of attached foam would have been the same as the shuttle, detached foam might lose its relative velocity very fast at 6000 mph, making the relative velocity of the foam hitting the shuttle much greater than, say, a piece of ice or even metal which would have greater mass and might maintain its velocity better.

[ironman]

I agree the debris was decellerating (fast) while the shuttle powered on up. But the sequence takes place clearly over at least a second. So let's estimate it traveled (relative to the orbiter) its entire length (122 ft) in 1 sec. This equates to around 80 mph. Just a WAG. But this clearly might have indeed done the fatal damage.