(05/07/1998) --- STS-91 Mission Specialist Franklin Chang-Diaz, Ph.D., pauses on the 217-foot level of Launch Complex 39A after the completion of Terminal Countdown Demonstration Test (TCDT) activities. Behind him, the Space Shuttle Discovery is being prepared for flight. The TCDT is held at KSC prior to each Space Shuttle flight to provide crews with an opportunity to participate in simulated countdown activities. STS-91 is scheduled to be launched on June 2 with a launch window opening around 6:10 p.m. EDT. The mission will feature the ninth Shuttle docking with the Russian Space Station Mir, the first Mir docking for Discovery, the conclusion of Phase I of the joint U.S.-Russian International Space Station Program, and the first flight of the new Space Shuttle super lightweight external tank. The STS-91 flight crew also includes Commander Charles Precourt; Pilot Dominic Gorie; and Mission Specialists Wendy B. Lawrence; Janet Kavandi, Ph.D.; and Valery Ryumin, with the Russian Space Agency. Andrew Thomas, Ph.D., will be returning to Earth with the crew after living more than four months aboard Mir