Two astronauts on the US space shuttle Endeavour have completed a seven-hour spacewalk as part of an effort to repair the orbiting International Space Station.

Americans Heide Stefanyshyn-Piper (45) and Steve Bowen (44) cleaned and lubricated the station's three double solar antenna arrays attached to the orbiter's exterior, working in bulky spacesuits 354km above the Earth.

The spacewalk, the longest of the 15-day mission, which began on 15 November, was completed at 12.58am GMT on Sunday.

Stefanyshyn-Piper and Bowen, both US navy captains, worked on repairs of the ISS's starboard Solar Alpha Rotary Joint race ring and replacing trundle bearing assemblies. The worn-out parts will be taken to Earth for inspection.

The complex work was orchestrated by Shane Kimbrough (41) who was on a spacewalk along with Stefanyshyn-Piper on last Thursday.

The mission's fourth spacewalk, continuing the repair work, is scheduled for Monday.

The spacewalks are part of an ambitious "home improvement" project designed to double the station's crew capacity from three to six.

As the two astronauts worked on the exterior, the rest of the seven-strong crew ferried equipment from the Endeavour module to the ISS. Starting from last Wednesday, the team began installing a freezer and an oven for scientific experiments by NASA's Destiny Laboratory Module.

The additions also include two new sleeping quarters, exercise equipment, a second toilet, two more ovens and a refrigerator.

Meanwhile, NASA experts continued to work on problems with a $250-million urine processor unit that is designed to process urine, perspiration and bath water into drinkable water.

NASA said a centrifuge motor inside the distillation unit was running too slow and drawing too much electrical current.

Once in place, the unit would make it no longer necessary to regularly ferry vast quantities of water to the space station.

The device is essential for doubling the accommodation capacity. It would also be able to recycle the station's 6.8 tons of waste water produced each year.

AFP