[ironman]

You need to reconsider the relative velocity of the debris and the shuttle.

[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.