On July 12, 2011 American astronauts Ronald Garan and Michael Fossum performed a 6 hours and 31 minute EVA.
The space walkers packed a failed ammonia coolant pump into Atlantis' payload bay for return to Earth and unloaded a satellite servicing demonstrator carried to orbit aboard the visiting space shuttle. The spacewalkers also deployed a new materials science experiment, fixed a snagged wire in a base for the station's robot arm and wrapped a vacant docking port with a thermal cover.
Because Atlantis was launched with a reduced crew of four to accommodate possible rescue scenarios, the spacewalk was carried out by station’s flight engineers R.Garan and M.Fossum to reduce training time for the shuttle crew. As such, the EVA was considered an Expedition 28 spacewalk, but it was the final outing by any astronauts with a space shuttle in orbit.