The joint crew of Endeavour and the station was awakened at 5:03 a.m. EDT by Pink Floyd’s “Wish You Were Here,” played for lead spacewalker Dave Wolf.

Spacewalkers Chris Cassidy and Tom Marshburn will head outside at 9:58 a.m. to swap out all four of the remaining P6 truss batteries, a task that is expected to take about seven and a half hours. Two of the six original P6 batteries were changed out during the mission’s third spacewalk on Wednesday, but work was stopped when carbon dioxide levels in Cassidy’s suit began to rise, unexpectedly.

Battery Replacements During Fourth Spacewalk

STS-127 Mission Specialists Chris Cassidy and Tom Marshburn will tackle a challenging 7 ½-hour spacewalk today to finish swapping out batteries for the International Space Station’s oldest set of solar arrays.

Their outing will be devoted entirely to finishing the work started on the third spacewalk of the mission – removing old batteries from the Port 6 truss structure and transferring new batteries from the Integrated Cargo Carrier on the end of the station’s robotic arm to the empty sockets on the truss.

Pilot Doug Hurley and Mission Specialist Julie Payette will position Canadarm2 near the truss for the spacewalk and, once all of the battery swaps are complete, maneuver the carrier back into Endeavour’s cargo bay. That maneuver will require them to hand off the carrier to the shuttle’s arm for re-berthing by Hurley and Commander Mark Polansky.