[Hermann the Cherusker]

It's the relative velocity of the obiter vs debris that's important, not the rel.vel of those things vs earth. To know how fast the debris was going relative to the obiter, neglecting wind, you have to know the time, or distance the stuff fell(decelerated), both are known, and the acceleration of the rocket. I saw an est that it was about 80-150mph, but I didn't check it.

The debris doesn't have the hardness and density of brick though. It's either foam, or a thick frost layer.

Check out what can happen in a tornado, with winds of around 200 mph. Things like 2x4's get punctured through thick brick walls, straw and twigs can punch holes through glass, etc. Anything hitting a brittle ceramic material at speed is bad news.

[sd-joe]

"Anything hitting a brittle ceramic material at speed is bad news."

True, but did you see the report on the inspection after flight STS-87, posted by Jael. Note the small part quoted below.
They also stated that when that occured, there was a relative wind of Mach 2 to Mach 4 (Wow).

THE MAIN THING TO REMEMBER IS THAT WITH THIS MUCH DAMAGE TO THE TILES, THE FLIGHT STILL RETURNED SUCCESSFULLY.

"Three hundred and eight hits were counted during the inspection, one-hundred and thirty two (132) were greater than one inch. Some of the hits measured fifteen (15) inches long with depths measuring up to one and one-half (1 1/2) inches. Considering that the depth of the tile is two (2) inches, a 75% penetration depth had been reached."