Space Motion Sickness (SMS) is an operationally significant problem during Space Shuttle Missions. Symptoms of SMS include loss of appetite, malaise, lethargy, retching, vomiting, a strong desire to keep the head still, and decrements in performance. The most severe levels of SMS include multiple incidents of retching or vomiting and performance decrements that last as long as 72 hours. NASA research has found that through 34 missions (STS-l through STS-34) 67% of Shuttle crew members experienced some degree of SMS during their fITst mission (Davis, Vanderploeg, Santy, Jennings, & Stewart, 1988; Davis & Beck, 1990). 48% of these astronauts experienced "mild" SMS, 34% experienced "moderate" SMS, and 17% experienced "severe" levels of SMS. Since STS-26 (Challenger) 26 crew members have been involved in subsequent missions. Twelve of these 26 crew members (46%) showed symptoms of SMS. Fifteen crew members reported no change in their symptomology, while nine indicated that their symptoms were less severe. Two reported that symptoms were worse in subsequent missions. Incidence of SMS among "experienced" crew members (those who flew subsequent missions) was not statistically different from the incidence among crew members on their first flight (Davis & Beck, 1990).