Astronauts board space shuttle for Florida launch

CAPE CANAVERAL, Florida (Reuters) - Space shuttle Endeavour's seven astronauts climbed aboard their spaceship on Friday for the start of a 15-day mission to remodel the International Space Station for an expanded crew.

Liftoff was scheduled for 7:55 p.m. EST/0055 GMT on Saturday from the Kennedy Space Center in Florida.

NASA plans to double the size of the space station crew from three members to six next year. The shuttle carries two new sleeping compartments and a water recycling system that will enable the crew to purify urine and other wastewater for drinking.

"We did blind taste tests of the water," said NASA's Bob Bagdigian, the system's lead engineer. "Nobody had any strong objections. Other than a faint taste of iodine, it is just as refreshing as any other kind of water."

"I've got some in my fridge," he added. "It tastes fine to me."

Delivery of the $250 million wastewater recycling gear is among the primary goals of NASA's 124th shuttle mission. Meteorologists predicted a 70 percent chance the weather would be suitable for launch.

If the shuttle lifts off on time, it would arrive at the space station on Sunday. Astronauts will then spend 11 to 12 days making home improvements.

In addition to the sleep chambers and the water recycler, Endeavour carries the station's first refrigerator, new exercise gear, and perhaps most important for a growing crew -- a second toilet.

"With six people you really do need to have a two-bathroom house. It's a lot more convenient and a lot more efficient," said Endeavour astronaut Sandra Magnus, who will take over as a space station flight engineer from Greg Chamitoff.

Chamitoff has been aboard the outpost since the last shuttle flight in June.

SHUTTLE SUPPLIES DRYING UP

Reusing water will become essential once NASA retires its space shuttles, which produce water as a byproduct of their electrical systems. Rather than dumping the water overboard, NASA has been transferring it to the space station.

But the shuttle's days are numbered. Only 10 flights remain, including a final servicing call to the Hubble Space Telescope. NASA is preparing to end the program in 2010, after which Russian Soyuz spacecraft will be the only way to ferry crew to the space station.

"We can't be delivering water all the time for six crew," said space station flight director Ron Spencer. "Recycling is a must."

NASA expects to process about six gallons (23 liters) of water per day with the new device. The goal is to recover about 92 percent of the water from the crew's urine and moisture in the air.

The wastewater is processed using an extensive series of purification techniques, including distillation -- which is somewhat tricky in microgravity -- filtration, oxidation and ionization.

The final step is the addition of iodine to control microbial growth, Bagdigian said.

The device is intended to process a full day's worth of wastewater in less than 24 hours.

"Today's drinking water was yesterday's waste," Bagdigian said.

(Editing by Jim Loney)