Washington  - Two astronauts from the Discovery space shuttle on Saturday performed maintenance work on the International Space Station during a second spacewalk, according to US space agency NASA.

US astronauts Steve Swanson and Joseph Acaba swapped out batteries, installed a new GPS antenna on the station's Japanese Kibo lab and took photographs of the station's radiators, one of which is damaged.

The spacewalk ended at 2321 GMT and lasted six and a half hours.

On Friday, the Discovery crew completed installation of the station's final pair of solar panels, which will expand the satellite's power supply.

During their first spacewalk Thursday, astronauts installed part of a crucial new solar panel on the ISS.

The 300-million-dollar panel is part of a truss segment that will complete the backbone of the station and boost its energy capacity, allowing the resident crew size to double to six astronauts.

Discovery docked Tuesday with the ISS, bringing the fourth and final solar panel.

The mission also delivered astronaut Koichi Wakata, who has officially joined the permanent crew on the orbiting space station as its first Japanese member. He replaces US astronaut Sandra Magnus, who will join the Discovery crew for the flight back to Earth.

The shuttle launched last Sunday after weeks of delays to inspect and study the hydrogen fuel valves and a later leak in a fuel vent.

Discovery is scheduled to end its 13-day mission on March 28. One more spacewalk is scheduled for Monday. (dpa)