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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