Image: Mission Specialist Heide Stefanyshyn-Piper egresses the airlock at the beginning of the third spacewalk of the STS-115 mission. Photo Credit: NASA TV

Astronauts Joe Tanner and Heidemarie Stefanyshyn-Piper are rolling through STS-115's third spacewalk. They are performing a wide-range of activities during the excursion, which is slated to wrap up about 12:20 p.m. EDT.

As of 9:05 a.m., the duo retrieved a materials exposure experiment from the exterior of the station and performed maintenance on the P6 truss.

The spacewalkers also performed tasks that allowed flight controllers to deploy the radiator located on the newly installed P3/P4 truss. The radiator will remove heat from the station. The P3/P4 was attached to the station on Tuesday and its solar arrays were unfurled Thursday.

Still on tap for the spacewalkers is the installation of a wireless TV antenna and replacement of an antenna assembly on the S1 truss. Near the end of the spacewalk, Tanner and Piper will conduct a test to evaluate infrared video of Space Shuttle Atlantis' wing leading edge.

Mission Specialist Dan Burbank is coordinating the spacewalk's activities, and Mission Specialist Steve MacLean is overseeing station robotic arm operations. During this mission, MacLean became the first Canadian astronaut to operate the arm built by his home country.

The start of the spacewalk was delayed due to a tripped circuit breaker that caused an airlock depressurization pump to lose power. After assessing the problem, flight controllers concluded that the issue was caused by a momentary electrical spike and that the pump did not have a short circuit. The spacewalk began at 6 a.m.