EARTH Aboard the International Space Station -- 08 Jul 2006 -- Astronaut Piers J Sellers, STS-121 mission specialist, participates in the mission's third and final session of extravehicular activity (EVA). The demonstration of orbiter heat shield repair techniques was the objective of the 7-hour, 11-minute excursion outside Space Shuttle Discovery and the International Space Station -- Picture by Lightroom Photos / NASA