Live in Orbit: Preps for Third Spacewalk

While efforts continue to activate a urine processor on the International Space Station (left), two former teachers are preparing to perform the third and last spacewalk of shuttle Discovery's 13-day mission.

The station earlier shifted its orientation to get out of the path of approaching space junk. Moving to a position used during undocking created a little drag that slightly lowered the orbit of the joined outpost and orbiter.

No further maneuver is believed to be necessary to avoid the remnant of a Chinese satellite, and Monday's spacewalk shouldn't be impacted.

Joe Acaba and Ricky Arnold have been reviewing procedures that were still being finalized today.

Monday morning, they'll return to the Unpressurized Cargo Carrier Attachment System that Acaba and Steve Swanson tried to install Saturday.

After lengthy analysis, NASA thinks the rotating platform on the Port 3 truss segment is just very stiff and stuck in place.

Astronauts normally don't pull things very hard in orbit to avoid damaging sensitive equipment, but that's exactly what the spacewalkers have been asked to do Monday.

"The fix for it may be as simple as simply pulling on it harder," said Kwatsi Alibaruho, the mission's lead space station flight director in Houston. "We won't really know until we get the spacewalkers at the site."

If that goes as planned, Acaba and Arnold will also try to install a second payload attachment system on the station's starboard side.

Later in the 6.5-hour spacewalk, Acaba and Arnold will move a cargo cart on the station's central truss, positioning it for a future shuttle mission; lubricate snares at one end of the station's robotic arm; and work on an electrical patch panel that powers station gyroscopes.

The duo has begun the standard pre-spacewalk campout in the reduced atmospheric pressure of the Quest airlock, a procedure that helps them avoid decompression sickness, otherwise known as "the bends."

Station commander Mike Fincke has made headway getting the urine processor up and running. Activation of a wet run stalled earlier today until a filtration assembly was switched out. Fincke now has the system in another dry run before trying again with urine flowing through.

The picture above show a microphone positioned to pick up noise and vibrations that would indicate if the system is working properly.