Astronauts complete unprecedented repairs to shuttles heat shield

By PAM EASTONAssociated Press Writer

SPACE CENTER, Houston (AP) - Armed with forceps and a makeshift hacksaw, a Discovery astronaut floated from the ship's airlock this morning for an unprecedented spacewalk to eliminate a potential source of dangerous overheating during the shuttle's re-entry.

Astronaut Stephen Robinson described his job as delicate, but simple: pull out or slice off two dangling pieces of filler material from Discovery's belly.

“OK Andy, I'm in the great outdoors,” Robinson told astronaut Andy Thomas after he followed spacewalking partner Soichi Noguchi out of the shuttle's airlock as it passed over Australia.

First, however, he and Noguchi, set out to install an external tool platform on the international space station, where Discovery has been docked since Thursday.

The platform's installation was the key task of the mission's third spacewalk until NASA officials determined the exposed ceramic-fiber fillers could lead to overheating and a repeat of the 2003 Columbia tragedy during Discovery's re-entry next week.

Columbia broke apart over Texas in 2003 as its crew returned to Earth from a 16-day mission. The disaster was blamed on a chunk of foam that fell from the external tank during liftoff and gashed one of spacecraft's wings. All seven astronauts died.

Discovery, set to land Monday, is the first shuttle to return to orbit since the tragedy. New damage surveys developed in Columbia's aftermath detected the drooping material on Discovery.

“We feel very comfortable we have a very doable task,” said David Wolf, who heads up Johnson Space Center's spacewalk branch. “Delicate is the word we want to stay with while we are at the bottom of the orbiter. We don't want to touch the tile if we can avoid it at all.”

Using a special foot restraint, Robinson rode the space station's 58-foot robotic arm as fellow astronauts aboard the station maneuvered it so he couldreach the shuttle's belly.

Robinson took only essential tools for the repair – leaving anything else he may need, including a tile repair kit, just outside the airlock. He also made sure to secure his safety tethers between his legs and behind him to prevent accidentally striking the vehicle.

Once under Discovery's belly, Robinson expected to spend about an hour removing or trimming the fillers from two locations near the shuttle's nose.

NASA officials think Robinson should be able to easily pull the first gap filler – about the thickness of three index cards bonded together – by using his gloved hand.

If a gentle tug doesn't work, he'll pull a little harder with forceps. And if he remains unsuccessful, Robinson will resort to a hacksaw put together in orbit with a deliberately bent blade, plastic ties, Velcro and the handyman's favorite all-purpose fix-it: duct tape.

“Because of the way this gap filler is sticking up at both ends, it does not appear to be bonded,” NASA officials told the crew in uplinked materials. “We expect it to slip out easily.”

Once he completes work at the first location, astronauts planned to reposition the station's arm so Robinson could reach the second protruding piece of filler, which sticks out about an inch.

That piece could be trickier.

NASA officials believe it remains glued to a shim that is bonded to a thermal tile.

There are 24,300 glass coated tiles on the shuttle, a majority of them on its belly. The tiles protect the shuttle from the extreme temperatures in orbit and, more importantly, insulate the ship during launch and re-entry.

The filler material protects the tiles from bumping against one another during launch, but isn't needed for landing because of the difference in the airflow.

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On the Net: NASA: http://www.nasa.gov/returntoflight/main/index.html