(03/31/1998) --- STS-90 Mission Specialists Dafydd (Dave) Williams with the Canadian Space Agency and Kathryn (Kay) Hire participate in Terminal Countdown Demonstration Test (TCDT) activities at KSC's Launch Pad 39B. The TCDT is held at KSC prior to each Space Shuttle flight to provide crews with the opportunity to participate in simulated countdown activities. The Space Shuttle Columbia is targeted for launch of STS-90 on April 16 at 2:19 p.m. EDT and will be the second mission of 1998. The mission is scheduled to last nearly 17 days