(03/23/1998) --- The Space Shuttle Columbia continues up the ramp to Launch Pad 39B in its morning rollout prior to STS-90. Leveling systems within the crawler-transporter underneath the Shuttle keep the platform level while negotiating the five percent ramp leading up to the pad surface. The top of the orbiter is kept vertical within plus or minus 10 minutes of arc, about the diameter of a basketball during the journey. The Neurolab experiments are the primary payload on this nearly 17-day space flight. Investigations during the Neurolab mission will focus on the effects of microgravity on the nervous system. The crew of STS-90, slated for launch April 16 at 2:19 p.m. EDT, includes Commander Richard Searfoss, Pilot Scott Altman, Mission Specialists Richard Linnehan, Dafydd (Dave) Williams, M.D., and Kathryn (Kay) Hire, and Payload Specialists Jay Buckey, M.D., and James Pawelczyk, Ph.D