HOUSTON – Three spacewalks down. One to go. Astronauts Stephen Bowen and Robert "Shane" Kimbrough venture outside the international space station Monday for the fourth and final spacewalk of space shuttle Endeavour's nearly two-week visit to the orbiting outpost.
The spacewalkers hope to finish unjamming a huge joint that keeps a power-generating solar wing on the space station's right side facing the sun. The joint hasn't been used much since September 2007 because parts were grinding, shaving off metal shards that jammed it and kept it from rotating toward sunlight. That limited the amount of energy the wing could produce.
Space station commander Michael Fincke said power generated by the wing will help the outpost's crew expand from three to six residents next year and allow more research 220 miles above Earth.
"We're going to need every watt of that power," Fincke said Sunday.
Astronauts couldn't finish the cleaning and lube job after three spacewalks, so the task was added to the fourth. They also plan to lubricate a similar joint for the station's left solar wing. Other tasks include installing a video camera, spacewalk handrail and GPS antenna, as well as taking photos of equipment.
During the first spacewalk last week, a $100,000 tool kit floated away from lead spacewalker Heide Stefanyshyn-Piper as she tried to clean grease from a lubrication gun. That forced flight controllers to choreograph the other spacewalks with only one pair of grease guns. Endeavour commander Christopher Ferguson said Sunday that the shuttle's spacewalkers had overcome that loss with aplomb.
"We're jacking up the international space station, taking the wheels off, and we're bound to get a little dirty, a little dusty and meet a few surprise along the way," Ferguson said. "I think we've weathered this one just fine and come back with a lot of confidence."
Inside the space station, astronauts spent a fourth day Sunday trying to get a urine processor working. The processor is part of the newly delivered $154 million system that converts urine, sweat and condensation into drinking water.
Fincke and shuttle astronaut Donald Pettit tried to fix the problem by changing how a centrifuge in the urine processor is mounted, but the machine stopped running after 3 1/2 hours during a test run. During previous tests, the urine processor has worked for just two hours at a time before shutting down. A normal run is about four hours.
"It looks like we made things better, but we're maybe not there yet," Fincke told Mission Control.
Parts of the system that recycle sweat and condensation are working without problems.
Endeavour undocks from the space station on Thanksgiving Day and returns to Earth on Saturday.