During the second spacewalk of the STS-115 mission, first-time spacewalkers Dan Burbank and Steve MacLean devoted the day to the final tasks required for activation of the Solar Alpha Rotary Joint (SARJ). The SARJ is an automobile-sized joint that will allow the station's solar arrays to turn and point toward the sun. Burbank and MacLean released locks that had held the joint secure during its launch to orbit aboard Atlantis. As they worked, the spacewalkers overcame several minor problems, including a malfunctioning helmet camera, a broken socket tool, a stubborn bolt and a bolt that came loose from the mechanism designed to hold it captive. The stubborn bolt required the force of both spacewalkers to finally remove it.
Burbank and MacLean spent seven hours and 11 minutes outside the station, beginning their spacewalk at 4:05 a.m. CDT and completing it at 11:16 a.m. CDT. In addition to the SARJ work, they completed several "get-ahead" tasks during their time outside.
Once the spacewalk was completed, Mission Control began a planned four-hour activation and checkout of the SARJ. The checkout is designed to ensure all primary and backup systems on the mechanism are operating well. Early in the checkout, controllers engaged the first of two drive lock assemblies, DLA-1, and rotated the massive joint 180 degrees.
Later in the checkout, the procedure called for engaging a second drive lock assembly, DLA-2, and rotating the joint again 360 degrees. When controllers commanded DLA-2 to engage, they did not get an indication the drive assembly had properly engaged. Controllers then sent commands for a procedure designed to correct any poor engagement of the mechanism, but still did not receive an indication it had properly engaged.
Engineers are evaluating the concern and have temporarily delayed starting the deployment of the new solar arrays pending further work and checkout of the SARJ. The timeline allows ample time to continue working on the problem during the night and still complete the deploy of the arrays on Thursday as scheduled.