A rationale for space motion sickness.

Space motion sickness (SMS) still remains a problematic nuisance for a majority of fliers during their first 1 to 3 days in space and is an enigma to all concerned after almost half a century of spaceflight and extensive ground and in-flight studies. There is no known etiology consistent with observed signs and symptoms, and attempts to produce pre- and in-flight countermeasures have largely failed. Some medications for motion sickness (MS) have been partially effective, but must be used with caution due to their side effects. A hypothesis regarding SMS that is consistent with current knowledge of vestibular physiology and with observed and measured phenomena during SMS is presented.