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CAPE CANAVERAL, Fla. - STS-125 Pilot Gregory C. Johnson walks toward the shuttle training aircraft on the Shuttle Landing Facility at NASA's Kennedy Space Center in Florida. He will practice shuttle landings on the runway. The STA is a Grumman American Aviation-built Gulf Stream II jet that was modified to simulate a shuttle’s cockpit, motion and visual cues, and handling qualities. In flight, the aircraft duplicates the shuttle’s atmospheric descent trajectory from approximately 35,000 feet altitude to landing on a runway. The practice is part of a terminal countdown demonstration test, or TCDT, to prepare for launch. TCDT provides astronauts and ground crews with an opportunity to participate in various simulated countdown activities, including equipment familiarization, emergency training and a simulated launch countdown. Space shuttle Atlantis’ STS-125 mission to service NASA’s Hubble Space Telescope is targeted to launch Oct. 10. Photo credit: NASA/Kim Shiflett