richvan writes "NASA administrator Michael Griffin was recently interviewed by the Orlando Sentinel about his first nine months on the job. He covers topics such as foam, Challenger, Mars, the budget, the astronaut corps and intelligent design. Describing the reasons for the foam loss, he states 'Cycling of the tanks with cryogenic propellants - in fact, [super-cold] liquid hydrogen, because we don't see this problem with liquid oxygen - causes or exacerbates voids in the bond between the foam insulation and the tank and produces cracks in the foam. If and when those cracks propagate to the surface, with a crack connecting a void to the surface, then you have a mechanism for cryopumping. When the tank is cold, air is ingested. It liquefies and goes into the voids. Then as the tank empties and the [air] warms up and evaporates, the resulting pressure blows the foam off.'"