Mission Specialist Steven Smith waits his turn at driving the M-113 carrier part of Terminal Countdown Demonstration Test activities.

STS-110 Mission Specialist Steven Smith waits his turn at driving the M-113 armored personnel carrier, part of Terminal Countdown Demonstration Test activities. TCDT includes emergency egress training and a simulated launch countdown, and is held at KSC prior to each Space Shuttle flight. Scheduled for launch April 4, the 11-day mission will feature Shuttle Atlantis docking with the International Space Station (ISS) and delivering the S0 truss, the centerpiece-segment of the primary truss structure that will eventually extend over 300 feet