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