English: Dwarfed by space shuttle Discovery, NASA astronauts Rick Mastracchio (right) and Clayton Anderson, both STS-131 mission specialists, are seen working in Discovery's aft payload bay during the mission's third and final session of extravehicular activity (EVA) as construction and maintenance continue on the International Space Station. During the six-hour, 24-minute space-walk, Mastracchio and Anderson hooked up fluid lines of the new 1,700-pound tank, retrieved some micro-meteoroid shields from the Quest airlock's exterior, relocated a portable foot restraint and prepared cables on the Zenith 1 truss for a spare Space to Ground Ku-Band antenna, two chores required before space shuttle Atlantis' STS-132/ULF-4 mission in May. Earth's horizon and the blackness of space provide the backdrop for the scene.