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STS-125 Mission Specialist Michael Good is helped by suit technicians to don a harness over his launch and entry suit before entering space shuttle Atlantis for a simulated launch countdown. The countdown is the culmination of terminal countdown demonstration test, or TCDT, activities as preparation before launch. TCDT provides astronauts and ground crews with an opportunity to participate in various launch activities, including equipment familiarization, emergency training and the countdown. Atlantis’ STS-125 mission to service NASA’s Hubble Space Telescope is targeted for launch Oct. 14.