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KENNEDY SPACE CENTER, FLA. -- STS-123 Pilot Gregory H. Johnson tests the communications in his helmet before the launch dress rehearsal, culmination of the terminal countdown demonstration test, or TCDT. The TCDT provides astronauts and ground crews with an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency training. Space shuttle Endeavour is targeted to launch March 11 at 2:28 a.m. EDT on the 16-day STS-123 mission to the International Space Station. Endeavour and its crew will deliver the first section of the Japan Aerospace Exploration Agency's Kibo laboratory and the Canadian Space Agency's two-armed robotic system, Dextre. Photo credit: NASA/Kim Shiflett