KENNEDY SPACE CENTER, FLA. -- STS-90 Mission Specialist Dafydd (Dave) Williams, M.D., with the Canadian Space Agency is assisted by NASA and United Space Alliance closeout crew members immediately preceding launch for the nearly 17-day Neurolab mission. Investigations during the Neurolab mission will focus on the effects of microgravity on the nervous system. Seen behind Williams also in an orange launch and re-entry suit is Mission Specialist Richard Linnehan, D.V.M. Williams and six fellow crew members will shortly enter the orbiter at KSC's Launch Pad 39B, where the Space Shuttle Columbia will lift off during a launch window that opens at 2:19 p.m. EDT, April 17 KSC-98pc508

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.