WASHINGTON - NASA is leaning toward flying its next space shuttle mission without the protective foam ramp that broke away from Discovery's external tank during its July return to flight, according to a spokesman for the U.S. space agency.
Shuttle officials plan to meet again this month to evaluate the Protuberance Air Load (PAL) ramp issue and possibly reach a decision.
"The data from the ongoing engineering analysis on the PAL ramp seems to be pointing in the direction of not flying with the PAL ramp for STS-121," said NASA spokesman Allard Beutel, referring to Discovery's next mission, tentatively slated for May 2006.
Beutel said eliminating the PAL ramp would not in and of itself jeopardize the May launch opportunity, provided that wind tunnel testing now being planned for February confirms that it is safe to fly without the structure.
The PAL ramp was added to the external tank early the program's history to provide a windbreak for a cable tray that runs along the tank.
NASA Space Shuttle Program Manager Wayne Hale raised the possibility of eliminating the ramp from the STS-121 tank during a Nov. 22 update on work the agency has done to eliminate foam shedding.
"In the long run, we have decided we would like to remove this fairly large piece of foam, just eliminate the hazard that it might cause," Hale said at the press briefing. "We think we have a very strong case to be ready to take that ramp off by the third flight tank. Some folks believe we can accelerate that and potentially even remove it for the STS-121 tank."
Several days after that press briefing, Beutel said, shuttle officials received new data that showed that recently discovered PAL ramp cracks on tanks undergoing inspection ran deeper than previously thought. The new data persuaded Hale that NASA should give serious consideration to removing the PAL ramp before STS-121. Hale shared this view with colleagues in a Nov. 29 e-mail first reported by the Washington Post.
Hale's Nov. 29 e-mail said nothing about schedule impact, according to Beutel, but in a separate internal memo, written in early September in the immediate aftermath of Hurricane Katrina, Hale concluded that flying STS-121 without a PAL ramp was not a realistic option since all the testing and analysis involved would delay the mission until late 2006.
Beutel, however, said shuttle officials now think they can safely remove the PAL ramp without forfeiting the May launch window.
"They've had a couple more months to work this and after studying this problem up and down the chain they are thinking that the PAL ramp removal is more feasible than they did just a couple of months ago," Beutel said.
Wind tunnel tests are being planned for February to evaluate the aerodynamic effects of removing the PAL ramp. In order to preserve the May launch window, Beutel said NASA would go ahead and ship the tank assigned to STS-121 to Kennedy Space Center in Florida without a PAL ramp.
"If, and only if, our further testing and analysis supports flying without a PAL ramp is aerodynamically alright to do, as our preliminary analysis indicates it would be, then the May launch window is still possible to make," Beutel said. "If our new testing and analysis indicates we need the PAL ramp, we'll stop our shuttle processing, reassess and work the issue from there."
He said NASA would also continue to investigate new ways of applying PAL ramp foam to prevent cracking that could cause the structure to break off during launch.
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