Live in Orbit: Fourth Spacewalk On Tap

The Endeavour astronauts will stage their fourth and final spacewalk outside the International Space Station today while colleagues inside the outpost continue work on a newly delivered system designed to convert urine into drinking water.

Shuttle mission specialists Stephen Bowen and Shane Kimbrough will venture outside the station at 1:45 p.m. EST, aiming to complete work on a faulty solar wing rotary mechanism on the starboard side of the station's central truss.

You can watch the action unfold here in The Flame Trench. Simply click the NASA TV box on the righthand side of the page to launch our NASA TV viewer and live 24/7 coverage of the STS-126 mission.

The spacewalkers also will lubricate an identical rotary joint on the port side of the girder-like truss in an attempt to avoid the type of trouble that's cropped up with its twin.

Two grease guns inadvertantly floated overboard during an initial spacewalk last week, but the crew is confident Bowen and Kimbrough can avoid mistakes and get the job done.

"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 surprises along the way," Endeavour commander Chris Ferguson said Sunday.

"I think we've weathered this one just fine, and we've have come back with a lot of confidence. We got the job done that we intended to do on the first three (spacewalks), and we're ready to go out there for the fourth one."

The shuttle and station crews are now up on this 11th day of the STS-126 mission. The Endeavour astronauts were beamed up a wake-up song -- "Can't Stop Loving You" by Van Halen. It was beamed up for Heidemarie Styefanyshyn Piper by her husband, Glenn Piper. The Expedition 18 crew aboard the station got a wake-up tone a little later.

The spacewalk today will focus on 10-foot-diameter rotary mechanisms designed to turn massive solar wings like paddlewheels so they remain pointed at the sun as the outpost circles Earth.

The rotary joint on the starboard side has been fixed in stationary positions since September 2007 because it hasn't been operating properly. Spacewalking inspections last year uncovered metal shavings that indicated internal parts were grinding as the mechanism turned.

The Endeavour astronauts are replacing bearing assemblies and lubricating the mechanism with a special space grease. The lubrication work on the portside mechanism is a precaution.

The 10 astronauts on the joined shuttle-station complex also will continue work with a new treatment system designed to convert urine, sweat and condensate into drinking water.

Trouble encountered during attempts to start up a urine processing assembly prompted repair work Sunday. Station skipper Mike Fincke did the job.

Preliminary tests indicated the repair work was successful. But then the system shut down again, so the astronauts will make another attempt to repair it today.

The system is key to pressing ahead with plans to increase the size of resident crews to six from three next May.

Endeavour's astronauts are scheduled to depart the station Thursday - Thanksgiving Day - and then land at Kennedy Space Center at 2:15 p.m. Saturday. A one-day extention of the shuttle's stay at the station remains an option. Landing in that case would be on Sunday.

ABOUT THE IMAGE: Click to enlarge and save the NASA TV screen grab. It shows the U.S. Quest airlock (center), which is connected to the U.S. Unity module of the International Space Station. The Unity module is a pressurized passageway between the American and Russia segments of the station. A Russian Soyuz spacecraft is shown docked to the Earth-facing side of the Functional Cargo Block, a space tug-turned-storage unit that was the first element of the outpost to be launched 10 years ago this month.