November 23, 2008 Spacewalk ends with most repairs complete Play video

(NECN/NASA) - 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 behind for another day.

As spacewalk 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 has 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.

Speaking in Texas, Houston, flight director for the mission, Ginger Kerrick, said trouble-shooting was planned on Sunday to find out why the urine processor assembly had broken down.

The problem could jeopardize NASA's plan to return recycled water to Earth aboard space shuttle Endeavour next weekend.

The 154 (m) million US dollar water recycling system, delivered a week ago by the space shuttle, is essential for allowing more astronauts to live on the space station next year.

Saturday's spacewalk 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

The astronauts got started on the unprecedented clean and lube job - and bearing replacements - on Tuesday.

Mission Control wanted to keep Saturday's spacewalk close to the seven-hour mark and, six hours in, told the astronauts to wrap up what they were doing and start heading back in.

Their spacewalk lasted almost seven hours, enough to make it the longest of the mission.

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 spacewalk of the mission on Monday.

Astronauts will grease up the good rotary joint on the left side of the orbiting complex.

Endeavour is due to leave the space station on the American holiday, Thanksgiving, but its departure could be put back a day in order to collect enough samples from the recycling equipment.