Florida ? Shuttle Discovery’s astronauts breezed through their third and final spacewalk Sunday, replacing an empty gas tank at the international space station and collecting a sample of dusty debris.

Spacewalkers Michael Fossum and Ronald Garan Jr. wrapped up their work so quickly that Mission Control threw in some extra chores.

The highlight of the 6 1/2-hour spacewalk, for Garan, was a long ride on the space station’s robot arm that swung him 80 feet out from the orbiting complex. He carried an empty nitrogen gas tank from one side of the station to the other, then returned with a full tank and plugged it in for use in the coolant system.

The spacewalkers performed a few more outdoor chores on Japan’s Kibo lab, which was installed last week, and hooked up a newly repaired camera elsewhere on the space station.

The spacewalkers squeezed in some stargazing as Garan rode on the robot arm. Fossum recalled how a schoolboy once asked him once whether he could see the stars during a spacewalk. “Indeed, you can,” Fossum said.