Animation shows the Pressurized Mating Adapter No. 2 docking port being removed from the station's Unity node by Atlantis' robot arm and temporarily stored on the Z1 truss. The PMA has to be removed to make way for Destiny's attachment to the station. Lead Flight Director Bob Castle explains the process, which occurs on Flight Day 4 during the mission's first spacewalk. Source video: NASA TV (340k, 42sec QuickTime file).