Discovery crew set for third spacewalk

Discovery spacewalkers overnight plan to complete a laborious job begun two spacewalks ago, the installation of a fresh ammonia supply for the International Space Station's cooling system.

Mission specialists Rick Mastracchio and Clayton Anderson are scheduled to set out on the mission's third and final planned spacewalk at 3:11 a.m. EDT Tuesday.

The outing is scheduled to last six hours and 30 minutes, and you can watch any of it here by clicking on the NASA TV box at right to launch a viewer.

Installation of the ammonia tank is one of the top objectives for Discovery's 14-day mission.

The first spacewalk, on Friday morning, removed a fresh tank from Discovery's payload bay and stored it in a temporary location. It was swapped Sunday with an old tank on the right side of the outpost's central truss.

At 2:16 a.m. Tuesday, the space station's 58-foot robotic arm will lift the old tank from a temporary parking spot and swing it down to the orbiter's payload bay, where the spacewalkers will later help bolt it into place for the trip home. They'll also hook up fluid cables to the new tank, a job they didn't have time to complete Sunday.

Assorted other planned tasks include picking up debris shields, removing a stowage platform from the Columbus lab for return home and work to help prepare for the next shuttle mission, by Atlantis.

Speaking of Atlantis, it's scheduled to roll from its Kennedy Space Center processing hanger to the Vehicle Assembly Building at 7 a.m. Tuesday, while the spacewalk is still in progress more than 200 miles overhead.

After Discovery's flight, three more remain -- one for each orbiter.

Inside the station, work will continue to stow the tons of supplies Discovery hauled up to the station. Much of what remains is now temporarily penned in "bungee jails" inside the Leonardo cargo module, awaiting transfer to its designated spot.

So far, about three quarters of the cargo transfer work is complete.

The crew is scheduled to awake at 10:21 p.m. Monday and go to sleep at 3:21 p.m. Tuesday.