Discovery's Heat Shield Successfully Repaired in Third Spacewalk
Mission specialist Steve Robinson approaches the underside of Discovery.
CREDIT: NASA TV.
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.
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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