Two US astronauts on Monday finished the fourth and last spacewalk of the shuttle Endeavour's mission at the International Space Station, completing all the tasks and repairs required of them, NASA said.

The "home improvement" mission at the orbiting station will be extended by one day with the Endeavour's return to Florida set for Sunday, a National Aeronautics and Space Administration spokesperson at Johnson Space Centre in Houston, Texas.

The spacewalkers, Steve Bowen and Shane Kimbrough, closed the hatch of the ISS decompression chamber at 12.31am GMT, ending their spacewalk, a commentator said on NASA television.

Their spacewalk lasted six hours, seven minutes — 23 minutes longer than planned.

The two astronauts finished cleaning, lubricating and replacing eleven of twelve ball bearings of a rotation device on one of the ISS's three double solar antenna arrays, or Solar Alpha Rotary Joint, which was stuck.

The space repair began during the first spacewalk a week ago, and on Tuesday the joint will be tested to see if it works properly.

The astronauts also installed a camera on one of the ISS's truss segments and a Global Positioning System on the Japanese Kibo laboratory module.

The four spacewalks brings to 118 the total EVAs — 745 hours, 29 minutes — used in building the ISS since its first segment was placed in orbit on 20 November 1998.

The orbiting structure is scheduled to be completed by mid-2010.

NASA decided to extend the Endeavour mission by 24 hours to 16 days, to give the astronauts time to fix a faulty urine processor unit they delivered that is designed to process urine, perspiration and bath water into drinkable water.

The problem, a centrifuge motor inside the distillation unit that was running too slow and drawing too much electrical current, has apparently been found and the $250-million machine should produce samples to be analysed back on earth, NASA said.

The device is essential for doubling the accommodation capacity, as it would be able to recycle the station's 6.8 tons 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.

Endeavour is set to undock from the ISS on Friday morning, and then land at the Kennedy Space Centre in Cape Canaveral, Florida, at around 1:18pm (6.18pm GMT) on Sunday.

Endeavour has delivered 14.5 tons of equipment to double the ISS' crew capacity from three to six.

AFP