THE international space station is about to go "green" with a fancy recycling water filter which will turn urine and condensation into fresh drinking water.

Later this week, space shuttle Endeavour's seven astronauts will carry the new water recovery system to the space station. Lift-off is set for midday Saturday, Sydney time.

This is NASA's first attempt at a closed-loop environmental system in orbit, where almost everything gets recycled. Already the power on the space station is generated from solar panels.

The water system is essential if NASA is to increase the size of the space station crew from three to six. That switch is supposed to occur by the middle of next year.

Endeavour's commander, Christopher Ferguson, says the benefits of the water system go way beyond the space station - think of all the deep-space exploration made possible once crews are freed of lugging water.

"This is really it, and it has no parallel. I would challenge you to find any other system on the Earth that recycles urine into drinkable water. It's such a repulsive concept that nobody would even broach it. But that day will come on this planet, too, where we're going to need to have these technologies in place, and this is just a great way to get started."

Would he drink the stuff?

"Are you crazy? I would never try that," Ferguson joked. "No, no, no, no. Actually, you know what? If they offered me a sample, I would do it."

Astronaut Donald Pettit, a former space station resident who will help hook up the system, looks at it as one big coffee machine. "It's going to take yesterday's coffee and make it into today's coffee," Pettit said. NASA does not expect to get the water generation system up and running before the northern spring. That's how long it will take to check everything and make sure the recycled water is safe to drink. Until then, the space station crew will continue to use water delivered by the shuttle and unmanned Russian supply ships.

Before Endeavour leaves, urine already collected by space station residents will be flushed through the system and undergo distillation, so recycled water samples can be returned to Earth for analysis. Additional samples will be brought back by another shuttle in February to make absolutely certain the system is working properly.

If everything goes well, the space station will open its doors to six full-time residents in May or June.

AP