CAPE CANAVERAL, Fla. -- On the heels of Christmas, NASA on Tuesday decided to delay this weeks launch of a resupply ship to the orbiting International Space Station to instead perform three spacewalks to repair a broken cooling system valve.
A failed valve on a pump module which controls the flow of coolant through lines to keep the space station's electrical systems cool stopped functioning on December 11 prompting NASA and the international partners to troubleshoot the exact cause and how to repair the issue.
"The pump is associated with one of the station's two external cooling loops, which circulate ammonia outside the station to keep both internal and external equipment cool," said Brian Dunbar, a NASA spokesperson at the Johnson Space Center near Houston.
Three designed six and a half hour space walks by two NASA astronauts will allow the space agency to uninstall the failed cooling pump module with a spare located on the Starboard Truss segment of the station.
The first spacewalk is planned to start on Saturday at 7:10 a.m. EST, and will see Rick Mastracchio and Mike Hopkins translate over to begin the prep work for the replacement work on the pump module.
A second spacewalk will take place on Monday to change out the pump, followed by a third space walk on Christmas morning to complete the installation and store the failed pump on the external stowage platform.
The third orbital walk will be only the second time in American history in which astronauts walked in space on Christmas Day. The first time occurred in 1974 during the Skylab 4 space station mission.
Meanwhile, in Virginia, a commercial resupply cargo craft was grounded until mid-January to allow for the three space walks.
An Orbital Sciences Cygnus craft, loaded with 2,780 pounds of fresh supplies and hardware for the six person station crew, was to have lifted-off on Thursday. Instead, the crew's attention will be focused on preparing for the three space walks followed by a Christmas break.
The Antares rocket loaded with the supply craft had been moved out to it's sea side launch pad at Wallops Island early Monday morning.
Orbital is set to become the second private company to have an operational spacecraft launch and dock to the orbiting complex, and later return completed science experiments and equipment after a splashdown recovery.
The Expedition 38 international crew spent Wednesday preparing the spacesuits needed to perform the exhaustive job, as well as review techniques and instructions for the installation.
A preplanned Russian spacewalk will then take place on Dec. 27 by two cosmonauts to prepare the orbiting lab for the arrival of a new science module in a few months.
Cosmonauts Oleg Kotov and Sergey Ryazanskiy will install new equipment, including a couple of high resolution cameras, install a new science experiment and a foot restraint.
(Charles Atkeison reports on aerospace, science and technology. Follow his updates via Twitter @AbsolutSpaceGuy.)