Astronauts are spacewalking again at the International Space Station in the third and final spacewalk of shuttle Discovery's mission.

Rick Mastracchio and Clayton Anderson floated out early Tuesday morning, an hour ahead of schedule. They will pick up where they left off Sunday, connecting fluid lines on the ammonia tank they attached last time. They also have to put the old tank aboard the shuttle, so it can be returned to Earth next week.

The refrigerator-size ammonia tanks are part of the space station's cooling system.

The spacewalkers had a little trouble opening the hatch. Mission Control asked them to check the handle before they left the air lock. Everything seemed to be in place.