NASA engineers
will patch up the last of four brackets with cracked insulation on the next
space shuttle fuel tank to fly Friday to help prevent the same type of foam
debris that dinged the Endeavour orbiter earlier this month.
Fuel tank
workers were a bit ahead of their nine-day schedule to strip
off cracked layers of ablative cork from the tank at the agency's Kennedy Space Center (KSC) in Florida, NASA
spokesperson George Diller told SPACE.com.
The fuel
tank repair must be complete before the 15-story vessel can be attached to the
twin solid rocket boosters that will help launch the shuttle Discovery on
NASA's planned Oct. 23 construction flight to the International Space Station
(ISS).
NASA
discovered the cracks in five brackets on Discovery's fuel tank during X-ray
scans after a piece of foam insulation popped free from Endeavour's own tank
and dinged
the orbiter's underbelly during an Aug. 8 launch. Only four of the five brackets
on the new tank are in need of repair, Diller said.
"We've
definitely found where our problem is," Diller told SPACE.com,
adding that Discovery's fuel tank could be attached to its rocket boosters by
Sept. 5 depending on the success of today's work.
The cracks
run through a layer of ablative cork and silicone, now found to be unnecessary,
sandwiched between the tank's aluminum brackets and their outer layers of lightweight
foam insulation. The brackets themselves help secure a liquid oxygen feed line
to the outer hull of the tank.
During Endeavour's launch,
a piece of foam - with the denser ablative material and possibly ice attached -
fell from the orbiter's fuel tank, then unexpectedly ricocheted off a metal
strut to etch a small gouge into the fragile heat-resistant tiles along its underbelly.
The damage posed no risk to the spacecraft or its seven-astronaut crew, but NASA
double checked its next three fuel tanks to fly and ultimately found cracks in
need of repair.
NASA has
worked to minimize the amount of shuttle fuel tank launch debris since a chunk
of foam damaged the Columbia orbiter
in 2003 at liftoff, leading to the loss of the spacecraft and its crew during
reentry.
On Monday,
engineers began the delicate task of cutting out the ablative layer on the brackets,
then recoating each area solely with foam insulation. The last two of the four
brackets under repair will receive new foam insulation today, Diller said.
Once engineers
cut down to the cracked ablative material, the cork-like substance simply popped
out, supporting suspicions that similar subsurface cracks led to the foam
debris that damaged Endeavour, Diller added. NASA officials have speculated
that the cracks may have formed during the fuel tank manufacturing process.
"Why it
was cracking, I think, is still a subject of some discussion," Diller
said. "But we've removed the source of the problem."
NASA was
already working on a permanent fix for its shuttle fuel tank brackets, which
involves replacing the aluminum fittings with new ones made of titanium, when
the cracks were discovered. The first tank with the new brackets is set to fly
on NASA's planned April 2008 shuttle flight.
Commanded
by veteran shuttle flyer Pamela Melroy, Discovery's STS-120 mission is slated
to deliver the new
Harmony connecting node to the ISS during a planned 13-day mission. When
finally installed, Harmony will serve as the foundation for the addition of new
international laboratories to the ISS.
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