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*Station’s First Module Reaches Orbital Milestone*

ISS's robotic arm, Orbital Boom Sensor System and Endeavour's robotic armImage above: The International Space Station's robotic arm prepares to hand off the Orbiter Boom Sensor System (OBSS) to shuttle Endeavour's robotic arm. Image credit: NASA TV TO VIEW IMAGE GO TO:http://www.nasa.gov/mission_pages/station/main/index.html

Zarya, the International Space Station’s first component to go into space, passed the 50,000th orbit mark at 11:17 a.m. EDT today. Zarya, which is Russian for “Sunrise”, was funded by the United States and built by Russia. It launched atop a Proton rocket from Baikonur Cosmodrome in Kazakhstan on Nov. 20, 1998.

Just before Zarya made its mark in the history books, STS-118 and Expedition 15 crew members used Canadian-built robotic arms to attach a third stowage platform on to the international outpost’s exterior. They used Space Shuttle Endeavour’s robotic arm to lift external stowage platform-3 out of the orbiter payload bay and hand it off to the station arm for installation on the Port 3 truss segment.

The new platform is the second component attached to the station since Endeavour and the STS-118 crew arrived Aug. 10. STS-118 spacewalkers installed the Starboard 5 (S5) truss segment on to the end of the Starboard 4 (S4) truss segment on Saturday. The S5 will serve as a spacer segment between the S4 and Starboard 6 (S6) segments. The S6 and its solar arrays will be attached during a future shuttle mission.

During the second STS-118 spacewalk, astronauts replaced a failed control moment gyroscope in the Z1 truss. The station has four gyroscopes that control its orientation in orbit.

Two more spacewalks are slated for the remainder of STS-118’s stay. The next is slated to take place Wednesday and will focus on preparing the Port 6 truss for relocation from atop the Destiny laboratory module to the end of the Port 5 truss when STS-120 visits later this year.

In other activities, the two crews have been transferring cargo between Endeavour and the station. STS-118’s stay at the station is slated to wrap up when Endeavour undocks Aug. 20.