Resolute - before you do your calcs, take a look at this:
All - this is a very interesting story, go to the story, not the bump link. Quote from the story:
In the Columbia's case, Crater predicted "significant tile damage," with gouge depths that actually exceeded the thickness of tiles in several critical spots. For example, the tiles protecting the wheel well are about two inches thick. Yet Crater calculated that the foam would penetrate 3.4 inches in this part of the wing.
The Boeing team did not accept Crater's predictions at face value. The program was "designed to be conservative," they noted, and so has sometimes "overpredicted penetration of tile coating significantly."
Another factor in their judgment was data from a 1992 Columbia mission that they believed had absorbed a "potentially" similar debris impact. In that case, the debris left a gouge only a half-inch deep.
There was a difference between the flights, though. In 1992, the debris was thought to have struck at an angle of 3.2 degrees. This time, the predicted angles were far sharper, which the Boeing team was careful to point out would alone significantly increase the damage. Still, for reasons not spelled out, the engineers concluded that "even for worst case," the foam debris would leave behind at least the last quarter-inch of tile, giving the wing at least some thermal protection.
The report did not spell out another thing: why the Boeing team never calculated how much worse the damage would have been if the debris was actually ice, or partly ice, and not foam.
As the Boeing team noted, previous NASA research had documented the dangers of ice debris: if it struck the wing's leading edge at a sharp enough angle — greater than 15 degrees — it could penetrate the tough carbon coating that protects the edge from re-entry heat, potentially leading to a catastrophic burn-through. In the Columbia's case, NASA calculated that the debris could have hit the edge at an angle of 22 degrees.
Outside experts, including many with deep institutional ties to NASA, are expressing polite concern that the engineers erred by not considering more possibilities.
"It was very good as far as it went," Dr. William Schneider, former assistant director of engineering for NASA, said of two reports prepared by Boeing engineers. But, he added, "They still needed to do more tests."
http://www.freerepublic.com/focus/news/845414/posts?page=3#3