Third Spacewalk Begins at 10:32 a.m. EDT

Spacewalkers Dave Wolf and Chris Cassidy began the STS-127 mission’s third spacewalk about 30 minutes ahead of schedule, at 10:32 a.m. EDT.

Wolf and Cassidy first will remove multilayer insulation from the Kibo module and prepare the Japanese Exposed Section payloads for their transfer from the Exposed Section to the Exposed Facility on Thursday. Then they will focus on battery replacements. The space station power system is a photovoltaic system that gathers solar power and stores it in batteries. Wolf and Cassidy will replace four of six old batteries in one of the six station power channels, channel 2B. In preparation for the task, the old batteries have been drained and the electrical loads normally handled by 2B have been placed on different power channels.

The new batteries are stored on the Integrated Cargo Carrier – Vertical Light Deployable, or ICC-VLD. Endeavour astronauts Doug Hurley and Julie Payette are using the space station robotic arm to move the ICC-VLD to the spacewalk worksite area near the Port 6 truss. Wolf and Cassidy will work together in a carefully rehearsed process to remove insulation from the old Port 6 batteries, install scoops to gently remove them, pass the batteries back and forth to a stowage location on the ICC-VLD, and repeat the process to replace them with the new batteries.

Each new battery assembly consists of 38 lightweight Nickel Hydrogen cells and associated electrical and mechanical equipment. Two battery assemblies connected in series are capable of storing a total of 8 kW of electrical power. This power is fed to the space station via the Battery Charge/Discharge Unit and Direct Current Switching Unit respectively. The batteries have a design life of 6.5 years and can exceed 38,000 charge/discharge cycles at 35% depth of discharge. Each battery measures 40” by 36” by 18” and weighs 375 pounds.

During today's spacewalk mission specialists Dave Wolf and Chris Cassidy will focus on the first set of battery replacements for the oldest solar array assembly on the International Space Station. The spacewalkers also will remove multilayer insulation from the Kibo module and prepare the Japanese Exposed Section payloads for transfer from the Japanese cargo carrier to the scientific front porch.

Shuttle pilot Doug Hurley and Canadian Space Agency astronaut Julie Payette will use the station’s Canadarm2 to assist Wolf and Cassidy during the mission's third spacewalk.