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KENNEDY SPACE CENTER, FLA. - In the White Room on Launch Pad 39B, STS-121 Mission Specialists Michael Fossum (center) and Piers Sellers have their launch suits checked by the closeout crew before entering Space Shuttle Discovery. They are connected to portable cooling units keeping them cool while waiting to enter Space Shuttle Discovery. The crew is taking part in a full dress rehearsal for launch, including countdown and culminating in main engine cutoff. The rehearsal is the final part of Terminal Countdown Demonstration Test (TCDT) activities that the crew has been involved in for two days. TCDT provides the crew of each mission an opportunity to participate in various simulated countdown activities, including equipment familiarization and emergency egress training. Mission STS-121 is scheduled to be launched July 1. Photo credit: NASA/Amanda Diller