Read all the latest news and see the latest images and video in our .
AFTER spending nearly $200 million and more than two years analysing and upgrading the shuttle’s external fuel tank and its problematic foam insulation, NASA is left wondering why pieces of foam fell off again during the launch of Discovery last week. Given that it was a piece of falling foam that doomed the shuttle Columbia in 2003, NASA has grounded its other shuttles until the problem is solved.
“This is something that has to be fixed,” said Discovery’s commander, Eileen Collins, during a radio interview from orbit. “I don’t think we should fly again unless we do something to prevent it from happening again.”
Advertisement
In January 2003, a 750-gram foam fragment damaged Columbia’s wing during launch, allowing superheated air to enter the wing and destroy the shuttle during re-entry. This time the falling foam did not strike the shuttle, but at least four pieces were large enough to cause serious damage. The largest piece was about half the size of the one that struck Columbia. Fortuitously, it broke off after more than two minutes of flight, at an altitude where the atmosphere is too thin and the air resistance too slight to slam foam into the shuttle with destructive force.
The largest piece of foam came from one of the fuel tank’s liquid hydrogen “protuberance air load” (PAL) ramps – a raised section of manually applied foam designed to keep rushing air from forcing its way under a set of cables. During modifications after the Columbia accident, a 3-metre section of the ramp was replaced, but the section that actually broke free during the Discovery launch had been declared safe to fly. “We came to the wrong conclusion,” said NASA’s chief administrator Michael Griffin. “We don’t want pieces of foam like that coming off.”
The incident underlines how little is understood about why foam breaks off. For example, concerns that cold, liquefied air might collect and expand in voids in the foam led engineers at Lockheed Martin, which manufactures the fuel tank, to extensively scan the PAL ramp using X-rays and a terahertz imaging system. The scan did not find anything suspicious, suggesting that the true cause of the shedding lies elsewhere. Griffin remained unperturbed: “I think we are going to fix it in short order, and we are going to get back flying.”
“That suggests to me that they already have some kind of solution in the drawer,” says Elisabeth Pate-Cornell of Stanford University in California, who was consulted by the Columbia Accident Investigation Board (CAIB). She warns that a quick fix to the PAL ramp could amount to “re-fighting the last battle”, and would not reduce the chance of foam falling off elsewhere on the tank. “It’s important to look forward,” she says. “Perhaps there are other problems.”
“I suspect we’re learning more about foam from this incident than we’ve learned in the last 20 years”
Some of these could be uncovered by images of Discovery’s launch. The new high-resolution cameras, a key recommendation of the CAIB report, have already confirmed that foam is a more serious and possibly more common problem than NASA thought. “I suspect that we’re learning more about foam from this incident than we’ve learned in the last 20 years,” says Stanford physicist and CAIB member Douglas Osherhoff.
