(04/07/2000) -- STS-101 Mission Specialists Mary Ellen Weber (left) and Jeffrey N. Williams (right) happily settle into their seats inside Space Shuttle Atlantis for a simulated launch countdown. The countdown is part of Terminal Countdown Demonstration Test (TCDT) activities that also include emergency egress training and familiarization with the payload. Other crew members taking part are Commander James D. Halsell Jr., Pilot Scott J. 'Doc' Horowitz and Mission Specialists James Voss, Susan Helms and Yury Usachev of Russia. During their mission to the International Space Station, the STS-101 crew will be delivering logistics and supplies, plus preparing the Station for the arrival of the Zvezda Service Module, expected to be launched by Russia in July 2000. Also, the crew will conduct one space walk to perform maintenance on the Space Station. This will be the third assembly flight for the Space Station. STS-101 is scheduled to launch April 24 at 4:15 p.m. from Launch Pad 39A