CAPE
CANAVERAL, Fla. -- NASA is weighing the benefits of several possible
modifications for space shuttle fuel tanks after a debris strike etched a deep
gouge in the Endeavour orbiter's underbelly last week, a top shuttle official
said Monday.
Wayne Hale,
NASA's space shuttle program manager, said a team of engineers are studying up
to five methods of tweaking fuel tank brackets to avoid the type of foam debris
hit that dinged Endeavour.
"The
all involve some reduction in the foam around the top of this little
bracket," Hale told reporters in a Monday briefing.
A small
piece of foam about the size of a baseball fell
from a bracket on Endeavour's fuel tank roughly a minute after the shuttle's
Aug. 8 launch. The shuttle is set
to land later today here at the Kennedy Space Center.
The
0.021-pound (about one-third of an ounce) foam chunk, which may have contained
some ice, unexpectedly ricocheted off a metal tank strut and gouged a deep, 3
1/2-inch by 2-inch (9-centimeter by 5-centimeter) long divot in the fragile
heat-resistant tiles on Endeavour's belly.
"We
didn't think this could happen before," Hale, adding that previous studies
predicted such foam debris would sweep harmlessly past an orbiter.
"Clearly, we're smarter now than we were a couple of weeks ago."
While the
resulting damage was later found to pose no risk to the safe
return of the orbiter or its seven-astronaut crew, NASA has found similar foam
shedding events on its last few shuttle flights. The damage from any such foam
loss to an orbiter's heat shield is not believed to be catastrophic, like that
which led to the 2003 Columbia
accident, but engineers are analyzing it just to be sure, Hale said.
The
increased frequency has prompted speculation that an extra hour added to launch
countdowns - to allow inspections teams to scan shuttle fuel tanks for ice
build-up - may actually contribute to ice formation that ultimately cracks or
looses foam debris.
NASA
engineers are already planning to replace the foam-covered brackets on fuel
tanks, beginning with a planned April 2008 shuttle flight, but discussion is
ongoing on whether an interim fix will be required. The space agency has
continually worked to avoid foam debris during liftoff since a chunk of the
insulation tore loose during the 2003 launch of Columbia and led to the
orbiter's destruction during reentry.
LeRoy Cain,
NASA's launch integration manager, told reporters last week that the space
agency delayed today's planned mating of the next shuttle fuel tank to fly to
its twin solid rocket boosters pending a final design change decision.
Trimming
some unnecessary foam insulation from the brackets or coating them in slick
solution or oil are among the possible modifications under discussion, he
added.
Any fuel
tank modification, if required, is not expected to add a major delay for NASA's
planned Oct. 23 launch of the shuttle Discovery to deliver the new Harmony
connecting node to the International Space Station.
"It's
a serious problem for us, and we recognize right away that we need to go
resolve it before we fly the next mission," Cain said.
But it could
affect a planned December flight aboard Atlantis to haul the European Space
Agency's Columbus laboratory to the station, Hale said. That flight has a slim,
week-or-so long window that opens Dec. 6 in which to launch towards the space
station, he added.
NASA has a
relatively tight schedule of at least 11 more shuttle flights planned to
complete space station construction by September 2010, when the agency's
three-orbiter fleet is slated for retirement
Nevertheless,
engineers will evaluate shuttle fuel tank safety between flights to identify
what type of fix, if any, will be ultimately required, NASA said.
"It's
just another day at the office," Hale said. "This is the kind of work
that we're into if we want to fly this vehicle throughout its manifest."
NASA is
broadcasting Endeavour's STS-118 mission live on NASA TV. Click here for mission updates and
SPACE.com's
NASA TV feed.
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