HOUSTON - For the first time in the history
of NASA's shuttle program, an astronaut has repaired the spacecraft's heat
shield in space during a spacewalk staged from the Discovery orbiter Wednesday
morning.
Discovery's
STS-114 astronaut Stephen Robinson used his own "A Number 1" fingers to pull
two strips of ceramic fiber cloth jutting out from between the heat-resistant
tiles lining the shuttle's belly. The repair
brings mission managers one step closer to clearing the orbiter's heat shield
for landing.
"It looks
like this big spaceship is cured," Robinson said as he plucked the final strip,
known as a gap-filler, from the starboard side of Discovery's forward section.
Robinson is
the first astronaut ever to get close to the vehicle's black ceramic
tiles--which protect space shuttles from the searing heat of reentry--in space. Mission managers sent him under Discovery's belly because
of concerns
that the gap-fillers could disrupt the aerodynamics experienced by the orbiter
during reentry and cause increased heating downstream on the tile surface and
wing leading edges. The space-filling material is used to prevent tiles from
grinding against one another during launch and to fill in excess space between
heat-resistant ceramics.
"Thanks to
the whole team for making this day super smooth and easy, as well historic," Robinson
told flight controllers and the spacewalk planning team.
The
spacewalk began at 4:48 a.m. EDT as the Discovery-International Space Station
(ISS) stack passed more than 200 miles over the southeast coast of Australia, marking the 61st
extravehicular activity (EVA) to support the ISS and the 28th to do
so from a U.S.
space shuttle.
A
damaged thermal
blanket, puffing out just below one of the flight deck windows at Discovery's
nose, is all that stands in the way of a clean bill of health for the shuttle's
heat shield. While not a thermal concern--shuttle officials said the blanket
could be removed entirely and pose no danger to the orbiter or its astronaut
crew--engineers are studying whether the small piece of fabric could separate
from Discovery during reentry and damage the spacecraft.
Orbiter repair
While not
the first on today's space work docket, the orbital repair was a highlight of
the EVA. By about 8:00 a.m. EDT (1200 GMT), Robinson had strapped into the
space station's robotic arm - controlled by STS-114 astronauts Wendy Lawrence
and James Kelly - and was on the move toward Discovery's heat shield.
Noguchi
watched from a vantage point on the ISS, while cameras aboard the station's
arm, Discovery's own robot arm-mounted orbital inspection boom and Robinson's
helmet recorded the repair.
"I'm
pulling now," Robinson said, as he removed the first gap-filler. "It's coming
out very easily."
The second gap-filler
followed just as easily about 10 minutes later.
"That came
out very easy, probably with even less force [than the first]," Robinson said
of the second gap-filler.
The repair
was completed at 8:55 a.m. EDT (1255 GMT) as Discovery and the ISS flew more
than 200 miles (321 kilometers) above the coast of France.
"You guys
are going to be really glad I brought a camera," Robinson said as he snapped
photographs of Discovery after the repair. "Nothing could look weird to me
after this."
"It's truly
spectacular, no other words," Robinson said.
Discovery's
STS-114 mission is the first shuttle flight since the 2003 Columbia disaster. Columbia's
seven STS-107 astronauts were killed when the orbiter broke apart over Texas while reentering
the Earth's atmosphere on Feb. 1, 2003. Investigators later found that damage
to Columbia's
heat shield--a puncture in its left wing leading edge from foam debris shed at
launch - allowed hot gases to enter and rip apart the vehicle.
NASA spent
two and half years and $1.4 billion to enhance shuttle flight safety and build
new in-flight inspection tools and procedures to evaluate shuttle thermal
protection systems while orbit. An unacceptable chunk of foam did fall from
Discovery's external tank at launch but did not strike the orbiter, prompting
officials to ground
its shuttle flight until the matter is understood and solved.
But the STS-114
flight has successfully demonstrated the use a new sensor-tipped inspection boom
and an orbiter backflip maneuver to allow
station-bound astronauts to photograph
shuttle tiles, both of which contributed to today's EVA.
"Everything
the team said would happen did," Robinson told flight controllers.
Late in the
spacewalk, flight controllers directed STS-114 mission specialist Charles Camarda and pilot James Kelly to use the boom to inspect
the damaged thermal blanket.
Space
station construction
In addition
to repairing Discovery's heat shield, the STS-114 spacewalkers also installed a
new spare parts platform outside the space station's Quest airlock, as well as
a materials exposure experiment that sent Noguchi scaling up to the highest
point atop the ISS.
Noguchi
installed the Materials International Space Station 5 (MISSE 5) at the top of
the P6 truss, which rises about 60 feet (18 meters) above Discovery's payload
bay. After attaching the experiment, Noguchi took a series of photographs to
capture the vast panorama of the ISS, shuttle and Earth below him.
Noguchi and
Robinson were not able to retrieve a broken rotary motor from the ISS to return
to Earth, nor perform a camera group installation due to the heat shield
repair, NASA officials said.
Today's
spacewalk was the last EVA scheduled for the STS-114 crew and the third excursion
for both Noguchi and Robinson. With the end of the EVA, both astronauts have
amassed 19 hours and five minutes of spacesuit-clad work time.
Robinson,
Noguchi and the rest of the STS-114 crew will now focus on completing cargo
transfer activities at the space station. A memorial to the lost Columbia astronauts is
slated for Aug. 4 at 8:04 a.m. EDT (1204 GMT) and undocking scheduled for Aug.
6 at 3:22 a.m. EDT (0722 GMT).
Discovery
is scheduled to return its STS-114 crew to Earth on Aug. 8 during an early
morning landing at Kennedy Space Center
in Cape Canaveral, Florida.
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