Image: Mission Specialist Steve MacLean works on a task during the second spacewalk of the STS-115 mission. Photo Credit: NASA TV

STS-115's spacewalkers Dan Burbank and Steve MacLean continue work to prepare the International Space Station's P3/P4 integrated truss for operation. The spacewalk began at 5:05 a.m. EDT and is slated to end about 11:25 a.m.

The 17.5-ton, 45-foot truss, which contains a set of solar arrays, was attached to the station Tuesday. The P3/P4 will provide power, data and communication services for the station. The arrays will be unfurled to a full length of 240 feet Thursday and will eventually double the station's power capabilities.

Burbank and MacLean removed 14 launch locks before turning their attention to six launch restraints on the Solar Alpha Rotary Joint, which will allow the arrays to track the sun.

About 7:10 a.m. EDT, MacLean reported that one of the four bolts on the cover to SARJ launch lock 8 was missing. The bolt had been there when he removed the cover to access the lock. MacLean reported he did not see the bolt in the SARJ mechanism. The cover is secure with three of the four bolts in place.

The duo is also scheduled to tackle tasks that were added due the success of the mission's first spacewalk. One of the get-ahead tasks is the preparation of the P3 truss for use by the Mobile Transporter – a platform that allows the station's robotic arm, Canadarm2, to move along the Integrated Truss Structure.

Mission Specialist Joe Tanner is serving as spacewalk coordinator. Mission Specialist Heidemarie Stefanyshyn-Piper is assisting Tanner and operating Canadarm2. Tanner and Piper conducted the first spacewalk and will perform the third Friday.

Meanwhile, the Expedition 13 crew is transferring cargo between Space Shuttle Atlantis and the station.