Astronaut Andrew Feustel, positioned on a foot restraint on the end of Atlantis' robotic arm, participates in Servicing Mission 4's third spacewalk on May 16, 2009. Over the six-hour, 36-minute spacewalk, Feustel and Astronaut John Grunsfeld removed the Corrective Optics Space Telescope Axial Replacement, installed the new Cosmic Origins Spectrograph, and worked to repair the Advanced Camera for Surveys.
