Two astronauts stepped back outside the International Space Station Wednesday on the last spacewalk of their mission after a brief delay caused by a minor spacesuit leak.

Discovery shuttle astronauts Steve Bowen and Alvin Drew donned their bulky NASA-issue spacesuits and turned the suits on to internal power at 10:42 a.m. EST (1542 GMT), signifying the start of the spacewalk. It's the second and final spacewalk of the mission -- Discovery's last spaceflight before being retired.

The start of the spacewalk was delayed slightly due to a leak in Bowen's spacesuit. The leak was traced to a faulty seal on the air-scrubbing lithium hydroxide canister in Bowen's spacesuit, which helps to remove carbon dioxide from the air inside the suit. [Infographic: Spacesuits Through the Years]

A replacement seal was inserted into the canister, successfully stopping the leak. This work set the crew behind schedule by about 25 minutes.

This spacewalk is the last for the crew of Discovery, NASA's most traveled space shuttle. The shuttle is making its final flight on this mission before being retired along with the rest of the shuttle fleet later this year. The 12-day mission is delivering a storage room and humanoid robot to the station.

Discovery crew's last spacewalk

To distinguish themselves for NASA cameras, Bowen is wearing a spacesuit with red stripes while Drew is wearing a solid white spacesuit. The excursion is expected to last approximately 6 1/2 hours.

Bowen and Drew successfully completed their mission's first spacewalk on Monday (Feb. 28) to install a power extension cable and move a faulty cooling pump module from a temporary attachment bracket to a storage platform on the station's exterior.

For today's outing, one of the major tasks will be to vent about 10 pounds of residual ammonia from inside the defunct cooling pump. The ammonia pump broke down last year and was replaced during a series of emergency spacewalks conducted by two space station astronauts during a previous spacewalk.

Bowen and Drew will also install a new flood light on the rail cart used to move cargo along the port side of the space station's backbone-like truss. Drew will then take a look at a loose radiator grapple beam on the port side of the truss.

Meanwhile, Bowen will install camera components on the Canadian-built, two-armed Dextre maintenance robot. He also plans to add a lens cap on the robotic Canadarm2 to protect it from being damaged by visiting spacecraft to the station.

Drew will then move to the station's Tranquility connecting module to remove thermal insulation covering a series of electrical connectors. Bowen will wrap another batch of insulation around the Dextre camera as well.

Extra space work

Mission Control planners here at NASA's Johnson Space Center also added a small extra task to today's orbital work:  removing a cover that is partially blocking the view from one of the cameras on the station's exterior.

On Monday's outing, Bowen and Drew installed a wedge beneath this camera, but a cover fell over part of the camera's lens in the process. During today's spacewalk, Drew will adjust the lens cover to give Mission Control a proper view from this camera's vantage point.

The spacewalk is expected to end at 4:48 p.m. EST (2148 GMT).

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