Two of shuttle Discovery's astronauts took an orbital walk today to prepare for a cooling system replacement and upgrade a navigation aid aboard earth's orbital outpost in space.
Rick Mastracchio and Clay Anderson began the first of three planned spacewalks this morning at 1:31 am EDT, as the pair placed their suits on internal power and opened the zipper hatch cover on the airlock on the International Space Station.
It was the start of the 141st spacewalk devoted to the construction of the space station.
First on the agenda had the spacewalkers translate over to the shuttle's payload bay and over to an ammonia tank located on the back wall of the bay.
The new ammonia tank was unbolted at 3:38 am, and Anderson then lifted the huge white box up to allow for the station's robotic arm to grapple it ten minutes later and slowly carry it over to station.
There are several ammonia tanks located on the outpost, and they provide cooling to the avionics and electronic systems.
As the Canadian-built robotic arm moved the ammonia tank over to a storage platform on the space station, Mastracchio and Anderson translated over to the Japanese Kibo module to retrieve a science experiment for it's return home to earth in one week.
A navigation aid known as the Rate Gyro Assembly was next on the crew's wrist-cuff checklist.
Mastracchio, performing his fourth spacewalk, unbolted the old gyro assembly and after a slight delay to free it, removed it at just before 6AM to allow for the new one to be installed on the starboard one truss.
Minutes after the installation of the new gyro, it was started by ground controllers and passed several aliveness tests.
The spacewalkers closed out a successful six hour, 28 minute spacewalk at 7:58 am, following the space duo's return to the airlock and suits placed on external power.
Today's orbital walk in space was Anderson's fourth, and he has now totaled 24 hours and 38 minutes of spacewalking time. Mastracchio has a combined spacewalking time which is two minutes more than his crew mate.
The combined orbital construction time outside the space station during the 141 'walks is now nearly 880 hours.
Anderson and Mastracchio will return out into the open vacuum of space on Sunday morning, and will replace the old ammonia tank with the new one.