When NASA's
Discovery orbiter rockets into space this year as the agency's first shuttle flight
in more than two years, the astronauts aboard will carry a bevy of tools and
techniques to ensure their spacecraft is safe.
In addition
to a redesigned, camera-laden external
fuel tank, the seven astronauts assigned to Discovery's STS-114 mission are
toting with them new instruments to repair the shuttle's thermal protection
system and a sensor-capped extension to the orbiter's robotic arm.
"We'll know
the health of our vehicle," said STS-114 pilot Jim Kelly during a recent
spacewalk training session
at in NASA's Neutral Buoyancy Laboratory tank at Johnson Space Center (JSC). "Once
we have that, we can make intelligent decisions if something were to happen."
Discovery
is currently set to launch no earlier than May 15 of this year to deliver tools
and supplies to the orbiting International Space Station and test its own new
equipment. The planned space shot is NASA's first shuttle launch since the loss
of the Columbia orbiter, which broke up during reentry, killing its seven
astronaut crew on Feb. 1, 2003.
Two tests for space
Discovery's
two spacewalkers, Soichi Noguchi of the Japanese Aerospace Exploration Agency
(JAXA) astronaut corps and NASA's Stephen Robinson, plan to test at least two techniques
to repair the array of tiles and reinforced carbon carbon (RCC) panels that
protect space shuttles from the heat of reentry.
"Tile and
[RCC] crack repair is difficult because the tiles are fragile," Robinson said after
completing the spacewalk training session. "And if they're damaged, they are
more fragile."
Noguchi
will test a new tool called the Emmitance Wash Applicator, which works somewhat
like a liquid glue stick to adhere material to shuttle tiles that boosts their
ability to emit heat.
A gray
substance, the wash, is loaded into a handheld applicator and squeezed through
a foam mesh to be dabbed over a damaged tile, explained Mark Dub, an extravehicular
(EVA) tool engineer at JSC. A layer ranging from one-eighth to one-twenty fifth
of an inch can be applied to tiles with damage reaching down to about half the
depth of a standard tile, he added.
While
Noguchi focuses on shuttle tiles during one of three STS-114 spacewalks,
Robinson will turn his attention to testing a technique to repair small cracks
in panels of reinforced carbon-carbon (RCC).
RCC panels
line the leading edge of shuttle wings and are designed to bear the highest
temperatures experienced during shuttle reentry. A hole punched by external
tank foam into one of Columbia's leading edge RCC panels at launch allowed hot
gases to enter the wing during reentry and destroy the orbiter.
"I'll be
looking at fixing cracked RCC panels using kind of a putty-like material,"
Robinson said.
The material,
a black, heat-resistance substance called non-oxide adhesive experimental
(NOAX), can be applied to an by squirting it through a space-hardened caulk gun,
then smoothing it to fill fine cracks in RCC panels - much like spackle - with
a sort of putty knife.
Other hardware
Discovery
is also expected to carry some additional tools for other repair
techniques, even if they're left stowed during the flight.
"It's like having
an ejection seat in a jet," Robinson said of the tools and techniques that aren't
planned for testing during STS-114 spacewalks. "You don't plan to use it, but
it's not a bad idea to have it along."
Among other
tools may be an array of overlay panels made of a material called carbon
silicon carbide that can be affixed over damaged shuttle tiles with screws.
NASA
engineer Kevin Wells, EVA tools project leader for overlay repair, told SPACE.com that while it is relatively
easy to install screws in shuttle tiles - they can be twisted using just a
finger - astronauts would have to use special tool to measure torque to ensure
the screw does not strip away needed material.
A second
set of patches, made of material similar to the overlays but a bit sterner, may
also fly during Discovery's mission. The patches are designed to fit over a
hole in a shuttle RCC panel, though researchers are still conducting ground tests
to make sure hot gases don't burn away or seep through patch edges.
"The gap
[between patch and panel] is the predominant path for failure," said Frank Lin,
NASA's project manager for RCC repair. "We could seal that gap with the NOAX
material."
One last
and potentially problematic repair method includes filling severely damaged
tiles with a pink, ablative goo-like substance called STA-54, which is squirted
into place from a backpack-mounted tank. The goo is actually made of two
separate materials that are mixed together as they pass through a handheld
device. STA-54 is designed to rise like bread as it heats up during reentry,
with outer surface ablating away and new material swelling up to take its
place, NASA engineers said.
Tests in
vacuum chambers and during zero gravity flights aboard NASA's KC-135 aircraft
have found that the STA-54 materials is prone to bubbling as it cures, which
could diminish its effectiveness if left unresolved.
Discovery's new reach
The largest
addition to Discovery's toolbox is a 50-foot (15-meter) boom
that can be attached to end of the orbiter's robotic arm in orbit, nearly
doubling its length.
A suite of
sensors, including cameras and a laser ranging system, should sit on the end of
the boom and allow the Discovery crew to scan the orbiter's underbelly for
cracked or broken tiles and other damage. Should that senor package fail, a
platform can be attached to the boom's end in order for an astronaut to make a
visual inspection and take digital images.
"We do have
to be prepared for the possible failure of the sensor package," Noguchi said.
Even without
the orbital boom and sensor package attached, Discovery's robotic arm has an
additional role for its first return-to-flight mission.
NASA
engineers said STS-114 astronauts have been training to perform a maneuver that
relies solely on the robotic arm, in which the manipulator will latch on the
International Space Station and turn the shuttle until its tiled belly is in position
for observation or repair.
"I don't
think that we're going too fast," Robinson said of Discovery's timeline and
NASA's push to resume shuttle flights. "The amount of questions remaining is
still very small."
advertisement
