(06/24/1999) --- STS-93 Commander Eileen M. Collins sits on the flight deck of the orbiter Columbia during Terminal Countdown Demonstration Test (TCDT) activities that include emergency exit training and a launch-day dress rehearsal culminating with a simulated main engine cut-off. Other crew members participating are Pilot Jeffrey S. Ashby, and Mission Specialists Catherine G. Coleman (Ph.D.), Steven A. Hawley (Ph.D.) and Michel Tognini of France, who represents the Centre National d'Etudes Spatiales (CNES). Collins is the first woman to serve as a Shuttle 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. The targeted launch date for STS-93 is no earlier than July 20 at 12:36 a.m. EDT from Launch Pad 39B