Spacewalker Steve Bowen works aboard the International Space Station's robot arm in this image from NASA TV March 2, 2011. [Photo/Agencies]

WASHINGTON - Two US astronauts ventured outside the International Space Station to conduct the second and last spacewalks for space shuttle Discovery' STS-133 mission on Wednesday, the US National Aeronautics and Space Administration (NASA) announced.

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According to NASA, Discovery's mission specialists Steve Bowen and Alvin Drew completed the spacewalk at 4:56 pm EST (2156 GMT), which lasted six hours and 14 minutes.

They vented ammonia from a failed pump module that NASA plans to return to Earth on the final shuttle flight in June, installed a camera and protective lens cover on the Canadian robot Dextre, added a light to a crew equipment cart, and removed an experiment platform from outside Europe's Columbus module. They also paused to snap pictures of NASA's launch site, as the shuttle-station complex sailed 220 miles (354 kilometers) above Cape Canaveral.

Discovery lifted off on Feb 24 from Kennedy Space Center in Florida and arrived the space station on Feb 26. This is 39th flight for Discovery, the first of the three surviving space shuttles to be retired this year.

When the US space shuttle program officially ends later this year, the Russian space program's Soyuz capsule will be the only method for transporting astronauts to and from the station.