Two days after the return of Discovery, NASA officials said that the next shuttle mission will probably be delayed until November because engineers have been unable to figure out why insulating foam fell off the spacecraft's external fuel tank.
Officials had been hoping to be able to clear up the foam problem in time for a September launch of Atlantis.
"We didn't find any root cause" for the foam incident, said William Gerstenmeier, the program manager of the International Space Station. "It was probably a combination of events. We just need to keep looking."
A 0.9-pound piece of insulating foam fell off Discovery's external fuel tank during launch last month. Although the foam didn't hit the orbiter, the incident caused the space agency to ground the shuttle fleet.
The loss of Columbia and its seven-member crew Feb. 1, 2003, was blamed on a similar piece of foam hitting and tearing a hole in the shuttle's left wing.
Gerstenmeier said in a teleconference call yesterday that five engineering teams are studying five cases of foam loss on the Discovery flight. The largest came off what is called the PAL ramp, a longitudinal ridge on the tank that serves to stabilize it during launch.
A second area of interest is the bipod area, which attaches the shuttle to the fuel tank. The bipod area, which was the source of the foam chunk that hit Columbia, had been extensively redesigned.
NASA spent several hundred million dollars over the past 30 months to address the foam problem.
Foam has been coming off fuel tanks, which contain the super-cooled liquid hydrogen and liquid oxygen, since the first shuttle flight in 1981. Until Columbia, upper management at NASA didn't believe the lightweight material could pose a danger to the spacecraft.