(06/21/1999) --- STS-93 Mission Specialist Catherine G. Coleman (Ph.D.) grins on her arrival at KSC's Shuttle Landing Facility aboard a T-38 jet to participate in Terminal Countdown Demonstration Tests (TCDT) this week. TCDT activities familiarize the crew with the mission, provide training in emergency exit from the orbiter and launch pad, and include a launch-day dress rehearsal culminating with a simulated main engine cut-off. Joining Coleman are Commander Eileen M. Collins, Pilot Jeffrey S. Ashby and Mission Specialists Steven A. Hawley (Ph.D.) and Michel Tognini of France, who is with the Centre National d'Etudes Spatiales (CNES). Collins is the first woman to serve as mission commander. The primary mission of STS-93 is the release of the Chandra X-ray Observatory, which will allow scientists from around the world to obtain unprecedented X-ray images of exotic environments in space to help understand the structure and evolution of the universe. Chandra is expected to provide unique and crucial information on the nature of objects ranging from comets in our solar system to quasars at the edge of the observable universe. Since X-rays are absorbed by the Earth's atmosphere, space-based observatories are necessary to study these phenomena and allow scientists to analyze some of the greatest mysteries of the universe