Insulation Debris - Cause of the Disaster

When members of the Columbia Accident Investigation Board (CAIB) issued their findings on the disaster's cause, those findings coincided with the concerns some NASA employees had expressed while the mission was still in progress. (See the various emails linked in this story.)

In short ... it is possible that a lightweight piece of debris (like the foam insulation) could cause a serious problem if it is traveling fast enough. From the CAIB report, Part One, Chapter 3:

The Orbiter "Ran Into" the Foam

"How could a lightweight piece of foam travel so fast and hit the wing at 545 miles per hour?"

"Just prior to separating from the External Tank, the foam was traveling with the Shuttle stack at about 1,568 mph (2,300 feet per second). Visual evidence shows that the foam debris impacted the wing approximately 0.161 seconds after separating from the External Tank.

"In that time, the velocity of the foam debris slowed from 1,568 mph to about 1,022 mph (1,500 feet per second). Therefore, the Orbiter hit the foam with a relative velocity of about 545 mph (800 feet per second).

"In essence, the foam debris slowed down and the Orbiter did not, so the Orbiter ran into the foam. The foam slowed down rapidly because such low-density objects have low ballistic coefficients, which means their speed rapidly decreases when they lose their means of propulsion."