Endeavour astronauts work on repairs on third spacewalk (AFP)

WASHINGTON (AFP) –

Two astronauts on the US space shuttle Endeavour were ahead of schedule on their spacewalk Saturday, halfway through the third repair mission on the exterior of the orbiting International Space Station.

Americans Heide Stefanyshyn-Piper, 45, and Steve Bowen, 44, were midway on the scheduled seven-hour spacewalk, working in bulky spacesuits almost 220 miles (354 km) above the Earth to complete repairs on one of the station's three double solar antenna arrays.

The spacewalk, the longest of the 15-day mission, which began on November 15, was half an hour ahead of schedule at 2000 GMT, after starting about 45 minutes early.

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 is being orchestrated by Shane Kimbrough, 41, who was on a spacewalk along with Stefanyshyn-Piper on Thursday.

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 work 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, 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 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.

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