By Liz White, UT staffWashington, DC-Causes of foam loss on the external fuel tank during last summer's July launch of the Discovery space shuttle are still being investigated by the US space agency NASA. And recent press reports say that the most recent findings, of deep cracks in the protuberance air load (PAL) ramp of one of the tanks currently in stock may mean further delays in launching the next mission. "At NASA's Michoud Assembly Facility in New Orleans, engineers continue evaluating the causes of this foam loss," which followed extensive evaluation and modification of the rigid polyurethane foam which insulates the liquid oxygen and hydrogen tank, said a 2 Dec statement from NASA. When NASA engineers took a detailed look at the PAL ramp of external tank No 120, they found "at least one crack that extends all the way to the tank's base foam layer." According to press reports, such cracks have been described in an internal NASA memo as resulting from contraction and expansion as the tank is being filled with liquid hydrogen and oxygen-and the problem is thus possible on the PAL ramp of any of the tanks. NASA's official statement said that evaluation of the cracks continues, to determine their cause and the possibility of flying STS-121-the next mission, due "no earlier than May 2006"-without the ramp."Preliminary analysis indicates it is aerodynamically feasible, but additional wind-tunnel testing will be scheduled to ensure flight integrity," said the NASA report. While work continues to meet the May launch window, NASA added that if the ramp is shown to be essential, processing of external tanks will stop "until requirements are assessed." The picture shows the jettisoned tank from the July 2005 Discovery launch, with the PAL ramp damage circled in white."
