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KENNEDY SPACE CENTER, FLA. - In the pre-dawn hours, STS-121 Commander Steven Lindsey walks across the Shuttle Landing Facility to the Shuttle Training Aircraft (STA). Lindsey and Pilot Mark Kelly will be making practice landings in preparation for the July 1 launch of Space Shuttle Discovery. The STA is a Grumman American Aviation-built Gulf Stream II jet that was modified to simulate an orbiter’s cockpit, motion and visual cues, and handling qualities. In flight, the STA duplicates the orbiter’s atmospheric descent trajectory from approximately 35,000 feet altitude to landing on a runway. Because the orbiter is unpowered during re-entry and landing, its high-speed glide must be perfectly executed the first time. Photo credit: NASA/Kim Shiflett