CAPE CANAVERAL — Spacewalking astronauts completed almost all of the greasy repairs on a gummed-up joint at the international space station on Saturday, leaving just a few chores for another day.
As space walk No. 3 was getting under way 225 miles up, 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.
Engineers on the ground scrambled to figure out what might be wrong. The problem could jeopardize NASA's plan to return recycled water to Earth aboard space shuttle Endeavour next weekend.
The $154-million water recycling system, delivered a week ago by Endeavour, is essential for allowing more astronauts to live on the space station next year.
Saturday's space walk by Heidemarie Stefanyshyn-Piper and Stephen Bowen was considered the most grueling of the mission and had been expected to last the longest, focusing 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.
Mission Control wanted to keep Saturday's space walk close to the seven-hour mark so it told the astronauts an hour beforehand to wrap up what they were doing and start heading back in. The remaining chores — cleaning and greasing one final section of the joint and installing the one more bearing — will be squeezed into the fourth and final space walk of the mission Monday. That's when astronauts will grease up the good rotary joint on the left side of the orbiting complex.
"We really appreciate how hard you're all working," Mission Control radioed. "I know it's painful to call it quits like that, but we think it's the right thing to do."
Stefanyshyn-Piper — who lost a $100,000 tool kit that included two grease guns during Tuesday's space walk — had to share grease guns with Bowen. To deal with the grease gun shortage, they carried a caulking gun normally used to repair the heat shield, but didn't need it.