NASA will not fly a protective foam ramp aboard the fuel tank for its next space shuttle mission, eliminating a potential launch debris hazard that cropped up during July's launch of the Discovery orbiter, a top agency official said Thursday.
Flying NASA's STS-121 shuttle mission - the second flight since the 2003 Columbia accident - without the ramp could push the spaceflight past a May 2006 launch window depending on the extent of modifications required, said William Gerstenmaier, NASA's associate administrator for space operations, in a teleconference with reporters.
Engineers have been discussing whether remove a protective protuberance air load (PAL) ramp from shuttle fuel tanks since July, when a one-pound chunk of foam insulation popped free from the ramp during Discovery's STS-114 launch. A similar foam shedding event doomed the space shuttle Columbia and its seven-astronaut crew in 2003 when it damaged the orbiter's heat shield.
"We think that's the best thing to do, just take it off," Gerstenmaier said, adding that meeting a May 2006 launch window comes second to solving the PAL ramp issues. "I think we ought not to think about May right now."
Last month, NASA shuttle officials said investigators had discovered a series of fine cracks along the PAL ramp of External Tank 120 (ET-120), which has been filled twice with supercold liquid fuel during tests and is one of several under scrutiny.
"We know a lot about the cracking phenomenon, but we still haven't pinpointed the cause," Gerstenmaier said, adding that solving the problem is critical not just for STS-121, but long-term shuttle program through its 2010 retirement date. "We know it's related to the chill down process and to some pressurization of the tank, but how those fit together...it's not an easy problem."
Once the problem is better understood, engineers will then decide the best fix for the external tank.
"We're going to do the right thing and let the data drive us where we need to go," Gerstenmaier said. "I think we've got a unique opportunity to get this right."
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