(Updates with quotes from inflight NASA news conference)

By Irene Klotz

HOUSTON, Nov 21 (Reuters) - NASA is having problems with a $250 million system it just delivered to the International Space Station to recycle urine and other wastewater into drinking water for astronauts.

But the glitches were not unexpected and will hopefully be ironed out in time for the visiting shuttle Endeavour crew to bring home its first samples, the U.S. space agency said on Friday.

The system shut down twice during initial attempts on Thursday and Friday to begin the distillation process on precollected samples of urine.

The system delivered this week is designed to recycle astronauts' urine and other wastewater into purified water for drinking. It will help clear the way for a doubling of the space station's crew to six members in May.

"I fully expected things not to work perfectly," station commander Mike Fincke said during an inflight news conference.

"No matter how well we plan on the ground or test on the ground, you really need to test-fly it and that's what we're doing here.

"We're very hopeful that we can get the first round of samples through during this mission while Endeavour is still here," he added.

The U.S. space agency needs the system to be running perfectly for 90 days before expanding the station's crew.

The shuttle arrived on Sunday and is scheduled to leave the outpost on Thursday. NASA wants the shuttle to bring home samples from the station's water purifier for analysis and may keep the ship and its crew at the station an extra day if needed.

"The No. 1 priority is to return the water sample," said Endeavour commander Chris Ferguson. "If we have to stay the extra day to do that we certainly will."

SHIPPING WATER TOO EXPENSIVE

Residents of the station will need to recycle their urine and other wastewater because the space shuttles, which produce water as a byproduct of their electrical systems, will no longer fly to the outpost after 2010 and it is too expensive to haul as much water as the crew will need on unmanned cargo ships.

"This technology of how to reuse our things and be careful with them is really applicable to planet Earth," Fincke said.

In addition to the water recycling gear, the shuttle astronauts delivered two new sleeping compartments, a second toilet, a galley and more exercise equipment.

Also on Friday, astronauts prepared for the third of four spacewalks to fix a problem with a joint in the station's truss. The 10-foot-wide (3-metre-wide) rotary joint is needed to position solar panels so they can collect light from the sun as the station orbits about 212 miles (341 km) above Earth.

Last year, NASA discovered one of the two joints had been damaged by metal filings and designed a complicated series of spacewalks to clean the joint, repair the damage and prevent it from happening to the other joint.

Space station managers estimate up to 10 spacewalks may be needed to resolve the problems.

The first four spacewalks were scheduled for Endeavour and its astronauts have completed two already, despite the loss of a $100,000 tool kit on Tuesday and a buildup of carbon dioxide in one astronaut's spacesuit near the end of the second spacewalk on Thursday.

The third outing is scheduled for Saturday.

NASA plans eight more missions to the station and a final servicing call to the Hubble Space Telescope before the shuttle fleet is retired in 2010.

Endeavour, which blasted off last Friday for a 15-day mission, is due back at the Kennedy Space Center in Florida on Nov. 29. (Editing by Tom Brown and Mohammad Zargham)

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