NASA engineers attached the
space shuttle Discovery's external fuel tank to its twin rocket boosters
Wednesday following a week of repairs to avoid the same type of foam debris
that dinged the Endeavour orbiter during liftoff earlier this month.
Shuttle workers are now readying
Discovery to move into NASA's Vehicle Assembly Building at the Kennedy Space
Center (KSC) in Florida in preparation for its planned Oct. 23 launch toward
the International Space Station (ISS).
Engineers spent just over a
week prying loose cracked
layers of cork insulation from a series of large brackets on Discovery's
external tank.
"There were not any
surprises and we found what we were looking to find," KSC spokesperson
George Diller told SPACE.com, adding that Discovery is due to roll over
to the 52-story Vehicle Assembly Building to be attached to its fuel tank on
Sept. 19.
The cracks were first
discovered in an X-ray survey of the tank after a piece of debris popped free
from a similar bracket during the Aug. 8
launch of Discovery's sister ship Endeavour. That debris ricocheted off a
metal strut and carved
a small gouge in Endeavour's tile-covered underbelly.
While the damage to
Endeavour posed no risk to the orbiter or the safe return of its astronaut
crew, NASA scrutinized its next three shuttle fuel tanks to fly to avoid
similar debris- shedding events in the future. The
space agency has worked to limit the amount of debris shed during shuttle
launches, while keeping a close watch on the integrity of orbiter heat shields,
ever since the 2003 loss of the
Columbia spacecraft and its astronaut crew.
During X-ray scans of Discovery's
fuel tank, engineers found cracks in a composite material of cork and silicone
known as super-lightweight ablator (SLA), which sits sandwiched between the
surface of an aluminum bracket and its outer layer of foam insulation. The
bracket is one of a series that secure a liquid oxygen feed line to the fuel
tank's outer hull.
The cracks may allow the
formation of ice when the fuel tank is pumped full of its super-chilled liquid
oxygen and liquid hydrogen propellant. The result could lead to the same type
of debris shedding as that which dinged Endeavour last month, NASA has said.
Since both the ablator
material and ice are denser than the lighter outer foam layer, they can cause
more damage to an orbiter's heat shield than foam alone, shuttle officials have
said. Engineers removed the ablator layers from four of five brackets with the
cracks on Discovery's fuel tank and plan future repairs for the next two tanks that
will support shuttle flights in December and February.
NASA is developing a
permanent solution, which will replace the aluminum brackets with new titanium
ones, that will debut on a planned April 2008 shuttle flight.
Commanded by veteran
shuttle flyer Pam Melroy, Discovery's STS-120 construction mission will deliver
the new
Harmony
connecting node to the ISS, where it will serve as a foundation for the
future addition of international laboratories. Once attached to its fuel tank
and rocket boosters, Discovery will roll out to its KSC launch pad in late
September, Diller said.
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