Repair Day For Discovery

Unprecedented Spacewalk Maneuver To Make Sure Shuttle's Safe To Fly Home

(CBS/AP)  The crew of the space shuttle Discovery is now attempting to do something that's never been done before: sending a spacewalker beneath the craft to repair filler sticking out from the ship's thermal tile belly.

NASA says the protruding material on the shuttle could cause dangerous overheating during re-entry and lead to another Columbia-type disaster.

Armed with forceps and a makeshift hacksaw, a Discovery astronaut floated from the ship's airlock just after 4 a.m. EDT Wednesday for an unprecedented spacewalk to eliminate a potential source of dangerous overheating during the shuttle's re-entry.

Discovery will remain docked at the space station until Saturday. The shuttle is set return to Earth early Monday.

CBS News Correspondent Mark Strassmann reports the repair being attempted Wednesday is considered to be fairly straightforward, and it is one the astronauts have trained for, although they have never actually tried in space.

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CBS News tech analyst Larry Magid speaks with astronaut Buzz Aldrin about the Discovery mission.

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

"Okay, Andy - I'm in the great outdoors," Robinson told astronaut Andy Thomas early Wednesday 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 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."