NASA's revolutionary new space water recycling system is having serious hiccups.

The $154 million device for turning astronauts' urine and sweat into drinking water aboard the international space station shut down again Friday, and engineers on the ground were scrambling to figure out why.

The astronauts and flight controllers are up against the clock: NASA wants samples of the processed urine before space shuttle Endeavour pulls away from the space station late next week. The recycled water needs to be tested back on Earth before anyone up there can drink it and NASA commits to doubling the size of the space station crew next year.

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No one was surprised by the startup trouble. Space station commander Mike Fincke said it's common for things to go wrong in a flight test and stressed that he wasn't worried — so far. Nor was he concerned about eventually drinking the final product.

"It's just the water that's taken out," Fincke said during a news conference. "It's really clean and purified water. In fact, it's probably more pure than most people's tap water. So I'm not afraid to drink it."

Of all the home-improvement gear delivered to the space station by Endeavour, the water recycling system has drawn the most attention. NASA sees it as the future in deep-space exploration — and also to future life on the home planet.

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

Converting urine into drinking water for space station astronauts is not all that different from what happens at water treatment plants on Earth — at a much smaller scale.

"What goes around comes around," said Bob Bagdigian, project manager at Marshall Space Flight Center in Alabama.

"The waste that we generate gets discharged somewhere, and that all becomes part of the water cycle through waste treatment systems," he said earlier this week.

Here's how the system works: Urine from the astronauts is distilled in a partial space vacuum, allowing the water to boil off. The distilled waste water is funneled into a mini-treatment plant that removes hair, lint and other contaminants, then goes through a series of filters. The water is actually put through a catalytic converter that cleanses via oxidation. As a final step, salts are added in the galley for taste.

The system's urine processor was started up as Thursday's spacewalk was ending, but promptly shut down.

Flight controllers reactivated the device early Friday. It ran for two hours before sensors detected motor problems and shut it down again.

If it's a bad sensor, it might be possible to bypass or repair it, Fincke said. But if the motor itself is at fault, NASA would have to send up a spare part on a future flight.

Flight director Courtenay McMillan said it was too soon to know whether NASA might have to give up on taking samples on this mission. If no samples come back aboard Endeavour, NASA will have to wait until another space shuttle arrives in February.

The system needs to be working before NASA doubles the size of the space station crew, from three to six. It hopes to do so by June.

The 10 space travelers on the linked space station and shuttle left it to flight controllers to sort out the urine processor trouble, and concentrated on other things Friday. They fired the shuttle thrusters to boost the attached station by a mile, and geared up for another spacewalk Saturday, the third one of the mission.

Endeavour is supposed to depart on Thanksgiving, but commander Christopher Ferguson said he'd be willing to stick around an extra day if that means bringing water samples home.

Bagdigian and others at NASA have worked on the recycling system since the mid-1980s, collecting urine and sweat from Marshall employees over the years to flush through test equipment on the ground.

Bagdigian admits he's biased, but says the recycled urine tastes fine. He handed out bottles of the urine-recycled water at the Nov. 14 launch of Endeavour — vintage 2005 — and popped open one for a liftoff toast.

The label on each of the commemorative bottles read: "We use only the finest ingredients!"