Two astronauts today began what is expected to be a six-and-a-half-hour spacewalk to repair a robotics system, along with cooling pump and a television camera on the International Space station.

NASA astronaut Reid Wiseman and Alexander Gerst of the European Space Agency set their spacesuits to internal battery power and then stepped outside of an airlock at 8:30 a.m. ET to begin their work.

Inside the spacecraft, flight engineer Barry Wilmore will operate the robotic arm to move Gerst around the space station during the spacewalk. Wilmore also is acting as the spacewalk coordinator, overseeing his partners' work.

One of the astronauts' tasks will be to install a mobile transporter relay assembly system, which provides backup power to the rail system that runs the length of the station. Robotic armsRobot Canadarm2 and Dextre move along the station's truss using this rail system.

Canadarm 2 is the space station's primary robotic arm, which is used to grab rendezvousing spacecraft, such as the SpaceX Dragon cargo craft.

Dextre a Canadian-built two-armed robot that stands 12-feet tall and has a 30-foot wing span. Dextre is used to reach into cargo ships and unload the supplies, spare parts and scientific supplies brought to the orbiter from cargo craft.

While Wiseman and Gerst are on the spacewalk, they'll also move a failed cooling pump from where it was temporarily stored on the station's truss to an external storage platform.

While Wiseman is cleaning up the area around the pump module, Gerst will replace a light on a television camera on another part of the station.

Live video of the space walk can be viewed on NASA's website.