UNDERCARRIAGE: Checking Discovery for damage
Jeff Kluger: It will never be possible to entirely prevent foam from flaking off the shuttle during liftoff — NASA administrator Michael Griffin has been quite candid about that. There's simply too much surface area on a fuel tank 15 stories tall, carrying more than 535,000 gallons fuel. There's too much wind and vibration during liftoff to prevent at least some foam from breaking off. What NASA engineers have done over the past two years is work to improve the contours, and the application of the foam, in the hope that no piece of foam that does break off exceeds .03 lbs., the weight at which the foam, at that acceleration, could begin to present the danger of serious damage. So what surprised NASA isn't that they lost a few bits of foam, but that one of the pieces that fell off was very big: Almost as big as the piece that killed Columbia, which weighed 1.67 pounds.
The large piece that fell off came from a 37-foot ridge that runs down the side of the tank protecting cables and fuel lines. All their testing had told them they had minimized this danger, but they hadn't — and the reason remains a mystery.
Does the fact that they've indefinitely suspended future shuttle missions suggest that they may be facing a problem they can't fix?
Yes, this may well be a problem that they can't fix, although the fact that NASA has stopped future flights also signals the much tighter safety standards that are now in place. Shuttles have been shedding tiles and foam for years, but luck and careful maintenance prevented tragedies. Then Columbia happened. Since then, NASA has narrowed the aperture of danger it is willing to tolerate. The current shuttle, by comparison to some of the previous missions, is remarkably clean despite the foam that fell off. In that respect, it shows that the work of the past two years has produced a lot of results. It's about as clean as a shuttle can be after liftoff, but having lost seven people to a foam-related, NASA has moved toward zero tolerance.
Is the damage to Discovery cause for concern about the fate of the current mission?
Well, there is some cause for concern, but it remains minimal. And not as a result of the large piece of foam that spun off relatively safely. The photographic inspection has revealed three divots on the underside of the craft, one of which is 1.5 inches long, adjacent to the wheel-well where the front landing gear is stored. If superheated gases stream into that open space during reentry, it can create a kind of vapor bomb inside the ship. But the photography suggests the divot isn't deep enough to cause that danger. So far, it looks like they'll be fine.