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 KSC-98pc451

The Space Shuttle program was the United States government's manned launch vehicle program from 1981 to 2011, administered by NASA and officially beginning in 1972. The Space Shuttle system—composed of an orbiter launched with two reusable solid rocket boosters and a disposable external fuel tank— carried up to eight astronauts and up to 50,000 lb (23,000 kg) of payload into low Earth orbit (LEO). When its mission was complete, the orbiter would re-enter the Earth's atmosphere and lands as a glider. Although the concept had been explored since the late 1960s, the program formally commenced in 1972 and was the focus of NASA's manned operations after the final Apollo and Skylab flights in the mid-1970s. It started with the launch of the first shuttle Columbia on April 12, 1981, on STS-1. and finished with its last mission, STS-135 flown by Atlantis, in July 2011.