(04/17/1998) --- STS-90 Mission Specialist Dafydd (Dave) Williams, M.D., with the Canadian Space Agency sits in a chair during suitup activities in the Operations and Checkout Building. Williams and the rest of the STS-90 crew will shortly depart for Launch Pad 39B, where the Space Shuttle Columbia awaits a second liftoff attempt at 2:19 p.m. EDT. His first trip into space, Williams is participating in this life sciences research flight that will focus on the most complex and least understood part of the human body the nervous system. Neurolab will examine the effects of spaceflight on the brain, spinal cord, peripheral nerves and sensory organs in the human body