Shuttle crew works on space station to-do list

Two astronauts floated outside the international space station Sunday and finished two of the maintenance tasks on their work list during the final spacewalk of the space shuttle Discovery's visit to the orbiting outpost.

Shuttle astronauts Michael Fossum and Ronald Garan Jr. finished the first and primary task of their excursion: replacing an empty nitrogen tank. Nitrogen gas is used to push ammonia through the station's main cooling system.

After the tank replacement, Fossum completed an extra task he had been given, collecting debris from a solar power wing's rotating joint.

Later in the spacewalk, they planned to remove insulation from wrist and elbow cameras on the robotic arm of the space station's newest room, the $1 billion Japanese lab named Kibo, as well as reinstalling a television camera that had a faulty power unit replaced.

The spacewalk, the third of the mission, began about 30 minutes ahead of schedule.

During the nitrogen tank replacement, Garan went on the ride of his life. While holding the old tank, he was attached to the end of the space station's robotic arm and was swung from the right side of the complex to the left. He was about 80 feet above the station during the maneuver. After getting the new tank, he was swung back to the right side, where he installed it.

“It's a lot different with the planet down there,” Garan said as he made the trip back with the new tank. The view from his helmet camera showed the space station with the Earth in the background.

“Yeah it is, isn't it a great view?” Fossum said.

“Unbelievable,” Garan said as the space station's orbit carried them over Peru.

In his extra task, Fossum collected samples of small amounts of dust-like debris detected on a solar wing rotating joint on the station's left side.

Engineers will analyze the debris to see if the material can help them figure out why a similar joint on the right side of the station was clogged with metal shavings.

That clogged joint on the right side of the station has been used only sparingly since last fall, hampering generation of electricity. The joints enable the space station's solar power arrays to rotate and track the sun.