home on the space station, as well as installation of the Materials International Space Station Experiment-6 (MISSE-6) and inspection of the station's right Solar Alpha Rotary Joint (SARJ).
This was the 109th dedicated to the assembly of the space station. Because the two made quick work of the major tasks, they also were able to remove trunnion covers on the Japanese Logistics Pressurized Module.
Behnken and Foreman, on the third spacewalk for each, first stored the Orbiter Boom Sensor System -- or OBSS -- on the station's truss. Normally, the OBSS is returned on the space shuttle but this time it is being left on the station because there is not enough room in the cargo bay of space shuttle Discovery to house the next Japanese component to the station -the massive Kibo science laboratory. Discovery will bring the OBSS back to Earth at the end of the STS-124 mission.
After the OBSS was stored, the two spacewalkers split up for other tasks. Behnken installed the MISSE-6 on the outside of the Columbus laboratory while Foreman inspected the SARJ.
The 10-foot-wide, 2,500-pound joint, which rotates the station's starboard solar arrays to track the sun, began showing increased vibrations and power usage last fall. Previous inspections have found metal shavings under the rotary joint's insulation covers, and Foreman again looked at an area previously photographed to better characterize an apparent pockmark.
This time around Behnken had no trouble with MISSE-6 thanks to a few troubleshooting methods developed by engineers on the ground. He and Mission Specialist Rick Linnehan had attempted to install the MISSE-6 experiment during the mission's third spacewalk, but were unable to engage latching pins used to hold the experiment packages onto the hull of Columbus.