Final Spacewalk of Discovery Mission Concludes

Shuttle Discovery astronauts performed the third and final spacewalk of their ten day visit to the International Space Station today.

Spacewalkers Rick Mastracchio and Clay Anderson began their venture outside the station at 2:14 am EDT, this morning as the pair switched their suit to internal power. Minutes later, they left the Quest airlock to begin a busy next six hours.

Today's spacewalk marked the final spacewalk ever to take place aboard Discovery, on this the second from last flight by the grand ol' ship.

The first chore of the orbital walk saw Mastracchio connect two nitrogen pressurization umbilicals and two ammonia transfer lines between the newly installed ammonia tank and the space station.

The pair exchanged an empty ammonia tank on Sunday with a new 1,700 pound tank which was brought up aboard Discovery last week.

Meanwhile, Anderson began retrieving the dual debris shields from their storage since last November to the airlock for their return home aboard Discovery in one week.

The two silver rectangular shields will be stowed later today in the Leonardo module.

"Wow, what a view," Anderson noted at late in the spacewalk at 8AM today as the orbital complex flew 213 miles off the coast of Mauritania, Africa. "The earth is a beautiful place," he added.

Over two hours into the sixth spacewalk for the orbital duo, the pair worked to stow the old ammonia tank into the aft section of Discovery's payload bay.

Using the space station's robotic arm, mission specialist Stephanie Wilson used the arm to lower the tank into position so that Anderson and Mastracchio could lower it into place and use four bolts to lock it down.

However, as is the trend in recent spacewalks over the past year, drama unfolded as Mastrscchio began having trouble with the alignment and boltdown of the spent tank.

Meanwhile, as the astronauts worked the torque wrench to get the bolts to turn the needed 16 times, controllers in Mission Control near Houston began having issues in the activation of the newly connected ammonia tank located on the Starboard Truss one.

An issue with a nitrogen valve is the likely issue as the ground continued to work the problem late into this morning.

Forty-five minutes of wrestling with the alignment of the tank's support bracket paid off and the bolts began turning and sinking into place.

The bolt wrenching delay forced NASA to delete the task of retrieving a European Space Agency experiment located outside of the Columbus module for it's return to earth.

"It's been awesome working with you guys, and Stephanie working robotics...", spacewalk coordinator Dottie Metcalf-Lindenburger told her crew from inside the station's Destiny laboratory as the spacewalk concluded.

Today's spacewalk concluded at 8:38 am, following six hours and 24 minutes of work outside in the harsh vacuum of space.

In total, Discovery's three spacewalks added up to 20 hours and 16 minutes; It was the 143rd spacewalk in support of space station construction and maintenance; and the 236th 'walk in the American space program's history.

In all, astronauts and cosmonauts have spent 893 hours and 33 minutes outside of the space station performing tasks and upgrades to build and resupply earth's outpost in space.