On July 22, 2009 mission specialists D.Wolf and C.Cassidy began the STS-127 mission’s third spacewalk at 14.32 UTC and ended it at 20.31 UTC when Cassidy’s CO2 levels increased more than expected as the two were in the midst of installing six new batteries used to absorb solar energy for electricity production when the station is not in sunlight. They completed two battery installations before ending the spacewalk. The remainder will be installed during the fourth spacewalk Friday.

While there was no immediate danger to Cassidy, rules called for termination of the spacewalk. This was the third of five spacewalks planned while Endeavour is docked to the station.