A Discovery astronaut successfully completed an unprecedented in-orbit shuttle repair during a space walk Wednesday by pulling from the shuttle's belly two pieces of protruding filler between the gap of heat protective tiles.

The task turned out to be easy as Stephen Robinson, one of Discovery's two spacewalkers, gently pulled out the protruding pieces of gap filler near the shuttle nose with his gloved hand in seconds instead of an hour as expected, without having to resort to a make shift hacksaw made of items from the international space station and prepared for cutting away the filler if needed. The spacewalk lasted about six hours.

NASA fears the protruding filler could cause dangerous overheating during re-entry, leading to a repeat of the Columbia disaster, which killed all seven astronauts on board in February. 2003.

The first astronaut who has ever ventured beneath an orbiting shuttle, Robinson was attached to the space station's 17.7-meter robot arm with a special foot restraint and carried to reach the shuttle's belly. The robot arm was controlled by fellow astronauts aboard the space station, who were very careful in operating so as to minimize Robinson's unnecessary contact with the ship. 

The repair task was thought very risky because Robinson could have done greater damage to the shuttle's fragile heat shield if he accidentally struck the shuttle during the spacewalk. His spacewalking partner, Soichi Noguchi, put a close watch on him and was set to communicate with the space station in case Robinson's communication system failed.

The shuttle has about 24,300 heat protective tiles, mostly on its belly, to protect it from the extreme temperatures in orbit, and insulate it during launch and re-entry. Gap filler is only needed to protect the tiles during launch.

After the repairs were completed and the spacewalkers returned, Discovery astronauts inspected a thermal blanket below the shuttle commander's window with the robot arm. The thermal blanket was ripped during launch, most likely by debris.

NASA engineers are assessing whether it is needed to do something to the blanket because it might come off during re-entry and hit the shuttle.

According to deputy shuttle program manager, Wayne Hale, it could be possible for NASA to plan an extra spacewalk to repair the blanket.

Discovery is set to return Earth on Monday. Its 13-day mission is the first shuttle flight since the Columbia disintegration.

(Xinhua News Agency August 4, 2005)