Two of space shuttle Discovery's astronauts aboard the international space station will perform a second spacewalk this evening to install a massive cooling tank on the outpost's port side.
Astronauts Danny Olivas and Christer Fuglesang are currently asleep in the Quest airlock on the space station as they prebreathe pure oxygen to purge the nitrogen from their system to prevent them from getting the "bends" during their spacewalk tonight.
The pair will begin the second of three planned spacewalks today at 5:19 pm EDT. The primary goal of the walk is to remove the new ammonia coolant tank from the payload bay of Discovery and transfer it where the old tank was removed from on Tuesday evening.
The largest mass spacewalkers have ever moved about in space, the 1800 pound ammonia tank will be slowly moved over to the Port 1 truss. At about 7:30 pm, it will be installed into place for use through 2015.
Olivas and Fuglesang will release several bolts holding the tank on a carrier in Discovery's payload bay. Then Fuglesang will put his feet in the foot restraints on the end of the space station's robotic arm as he picks up and carries the ammonia tank as astronaut Nicole Stott translates him over to the port 1 truss segment.
There the tank will be installed and coolant cables from the station attached.
On the subject of tonight's spacewalk, this reporter asked the chief of the flight director's office, John McCullough, during a NASA news conference Wednesday evening, "What technical differences are there between the new ammonia tank and the old one...?"
McCullough responded that he was unsure on any new advances in the new tank but that "this (new) one is full and that's the primary goal. The other one's been on orbit since 2002 and so it needs to come down and be refurbished; and the intension is to take it back up to station" on a later flight.
NASA will relaunch this older tank on Discovery's March 2010 flight on the STS-131 mission.
Also, overnight this morning, the crew of thirteen astronauts aboard the station-shuttle complex worked to unstow the Leonardo cargo module.
Discovery astronaut Jose Hernandez gave SpaceLaunchNews.com a "sweet-tweet" from orbit, "Moved items from the MPLM (Leonardo) to ISS. Similar to moving items from a moving truck and placing them in their final place at a new home!"
Over fifty percent of the cargo module has been unloaded and placed upon station. Leonardo will be undocked from the station's Harmony module on Monday and returned to the payload bay of Discovery.