WASHINGTON - TWO astronauts on the US space shuttle Endeavour completed a seven-hour spacewalk on Saturday, in the mission's third scheduled spacewalk to repair the orbiting International Space Station.

Americans Ms Heide Stefanyshyn-Piper, 45, and Mr Steve Bowen, 44, cleaned and lubricated the station's three double solar antenna arrays attached to the orbiter's exterior, working in bulky spacesuits almost 220 miles (354 km) above the Earth.

The spacewalk, the longest of the 15-day mission, which began on November 15, was completed at 0058 GMT.

Ms Stefanyshyn-Piper and Mr 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 Mr Shane Kimbrough, 41, who was on a spacewalk along with Ms Stefanyshyn-Piper on 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 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 new ovens and a refrigerator.

During an earlier spacewalk on Tuesday, Ms Stefanyshyn-Piper let slip her tool bag and watched helplessly as it floated off into the void of space. Mission Control at the Johnson Space Center in Houston however said the work on the ISS's solar antenna rotation system would continue as planned.

Meanwhile, Nasa experts continued to work on problems with a 250-million-dollar (S$382 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.

The device is essential for doubling the accommodation capacity, as it would be able to recycle the station's 6.8 tonnes of waste water produced each year.

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