Two US astronauts began a spacewalk Sunday to conduct repairs on the International Space Station, DPA reported.
During a planned six-and-a-half-hour spacewalk, astronauts Andrew Feustel and Mike Fincke are to refill one of the station's cooling units with ammonia and lubricate a joint that allows a solar panel to track the sun and provide the station with power.
It is the second of four spacewalks planned during the final mission of the space shuttle Endeavour, which docked Wednesday with the ISS.
The spacewalks are the last to be conducted by a shuttle crew and are designed to leave the space station in top shape before the shuttle is retired. The shuttle is the only craft large enough to bring bulky cargo such as parts to the station, though Russian, European and Japanese vehicles can bring smaller payloads.
The shuttle fleet is being retired after a 30-year history as NASA focuses its efforts on developing a long-range vehicle for travel to Mars and other distant destinations.
The US space agency hopes to contract with commercial spaceflight providers to provide the short missions to the ISS. While those craft are being developed, astronauts will be reliant on Russian Soyuz craft to lift them into orbit.