(AP) Astronauts stepped out for the longest and hardest spacewalk of their mission Saturday to wrap up greasy repair work on a gummed-up joint at the international space station.
As spacewalk No. 3 was getting under way, a new recycling system for converting urine into drinking water broke down again.
It was the third day in a row that the urine processor inexplicably shut down, and it appeared to be the same kind of sluggish motor trouble seen before.
The $154 million water recycling system, delivered a week ago by space shuttle Endeavour, is essential for allowing more astronauts to live on the space station next year.
Saturday's spacewalk by Heidemarie Stefanyshyn-Piper and Stephen Bowen focused entirely on the clogged solar wing-rotating joint. The joint stopped working properly more than a year ago, after it became jammed with metal grit from grinding parts, and cannot keep the solar wings on the right side of the space station pointed toward the sun.
The astronauts got started on the unprecedented clean and lube job - and bearing replacements - on Tuesday.
NASA expected Saturday's spacewalk repairs to last at least seven hours. Any chores left undone could be squeezed into the fourth and final spacewalk of the mission Monday. That's when astronauts are supposed to grease up the good rotary joint on the left side of the orbiting complex.
Stefanyshyn-Piper - who lost a $100,000 tool kit during Tuesday's spacewalk - had to share grease guns with Bowen 225 miles up. To make up for the grease gun shortage, they took out a caulking gun normally reserved for repairs to the shuttle's heat shield.
As for the broken urine-recycling system, flight controllers and astronauts alike were disappointed when it stopped working again Saturday. Mission Control radioed up the bad news just before the spacewalk began.
"I'm very sorry to hear that," astronaut Sandra Magnus replied.
Earlier Saturday, flight director Brian Smith said the machine for converting sweat and other condensation into drinking water was working fine, and that the two crews were trying to create more condensation in order to collect samples.
The astronauts turned off the air conditioner on the Russian side of the space station, cranked up the heat in the docked shuttle, and waited for condensation to form on equipment in the American compartments.
Even though there would be no samples of urine-converted water, at least there would be samples of processed condensation if the plan works, Smith said.
NASA wants samples of the recycled water returned aboard Endeavour in order to conduct tests and ensure that it's safe to drink. The equipment is supposed to run for at least 90 days before anyone takes a sip.
The space agency cannot expand the size of the space station crew from three to six unless the water recycling system is working. NASA still hopes for that to happen by June.
Endeavour is supposed to leave the space station on Thanksgiving, but its departure could be put back a day in order to collect enough samples from the recycling equipment.
For more information on Shuttle Mission 126, visit the NASA Web site.