Applications of Vestibular System Response to Mission Risk Mitigation Factors and Spacecraft Design Requirements

Forty to seventy percent of astronauts and cosmonauts reportedly exhibit undesirable vestibular disturbances during the first few days of exposure to weightlessness, including Space Motion Sickness (SMS) and perceptual illusions. While SMS is the primary concern for short-duration missions, the effect of perceptual illusions during landing may be particularly problematic following long-duration missions such as returning from the International Space Station (ISS), or a Mars mission, where vestibular, perceptual and sensorimotor adaptation to 1g, to 0g, to 0.38g has occurred. The longer the mission, the more complete the adaptation is to hypogravity and the more severe the perceptual errors and sensorimotor control disturbances. In addition, it is likely that the varying g-loads experienced during landing maneuvers will produce an even more pronounced response than might normally be experienced, as adaptation of the vestibular system may lead to hypersensitivity and/or sensory reinterpretation. This could, in a worst-case scenario, lead to difficulty controlling a piloted return vehicle. The current method for preventing and treating the detrimental effects of SMS for short-duration flights is pharmacological intervention. However, this approach has not yet proven fully effective, and the side effects of drowsiness and lack of concentration are undesirable in any mission phase. Pre-flight adaptation techniques may help to alleviate the concern in transitioning from 1g to 0g. In order to reduce vestibular disturbances during landing, the numerous orientation cues should be made as familiar and intuitive as possible to the pilot, thereby maintaining an effective “seat of the pants” tactile sense, as well as keeping other inputs in agreement with the vestibular system. However, even a normally familiar orientation will likely be unfamiliar to someone whose vestibular system has adapted to a different g-environment, so pre-landing adaptation training may be valuable in this phase. Therefore, it is logical that vestibular effects be considered for developing pre-flight and pre-landing adaptation training techniques, as well as for providing guidelines for future reentry vehicle design requirements.