Two U.S. astronauts stepped out the International Space Station on Tuesday to retrieve a failed ammonia pump, which is the last spacewalk of the shuttle era, NASA announced.

Space station astronauts Mike Fossum and Ron Garan completed the six-hour, 31-minute spacewalk at 3:53 p.m. EDT (1953 GMT). The duo retrieved a pump module from an external stowage platform on station and store it in shuttle Atlantis' cargo bay for return to Earth.

The pump module failed in 2010, shutting down half of the space station's cooling system. Engineers will evaluate the module to determine the cause of the failure and plan to refurbish it for use as a spare.

The astronauts also attached a Robotic Refueling Module experiment to the space station, which aims to test technologies for repairing and refueling satellites in space.

It was the 249th spacewalk by U.S. astronauts and the 160th spacewalk in support of space station assembly and maintenance, totaling 1009 hours, nine minutes.

Atlantis lifted off on Friday morning from Kennedy Space Center in Florida, on the 135th and final flight in NASA's shuttle program. Its return to the earth later this month will mark the end of the 30-year shuttle program.

 VietNamNet/Xinhuanet