NASA plans to retire the ageing fleet of shuttles at the end of next year.

The spacewalkers also removed insulation from Japanese experiments and moved handrails on the outside of the ISS.

It was the third of five planned spacewalks during the mission that brought a new porch to the Japanese Kibo laboratory. The four-tonne porch on the station's Japanese laboratory will be used to expose scientific experiments to the extremities of space through X-ray cameras and studies of cosmic dust.

The next spacewalk, which is also to focus on battery work, is set for Friday.