Many things we take for granted on Earth are radically altered in the space environment. For instance, the zero-gravity environment deprives astronauts of the cues they rely on to balance, navigate, and understand their relative position in space (e.g., gravity). The otolith organs (the main gravity sensors), semicircular canals, eyes and proprioception (position senses) make up the vestibular (balance) system. In space, the otolith organs and position senses are affected the most, as they rely most heavily on gravity. When these systems are thrown awry, the others are affected too, as input to the integrative centers does not agree. In this instance, visual cues carry more weight as astronauts learn to adapt to conflicting sensory input.
Astronauts adapt quickly in space. They begin to rely more heavily upon visual cues, as input from the otolith organs is suspect, altering sensory integration. They develop a new sense of tilt, as motion can be hard to sense in weightlessness. In a few instances, certain individuals find adaptation difficult and suffer chronic motion sickness, but such reactions are rare due to pre-flight screening. There are several tests – rotational testing, vestibular-ocular testing, posturography – that can assess the ability of an individual’s vestibular system to adapt. Such tests are useful in screening out susceptible individuals, as is key to Astro-Omics.
The effects of the space environment on the vestibular system are most evident right after astronauts switch from one environment to the other. When they arrive in the space environment, they often suffer from motion sickness, and have trouble sensing position and movement. Once they adapt, though, they are able to avoid these symptoms. Similarly, they have trouble balancing and walking once they return to Earth.
Currently, one of the most considered countermeasures is artificial gravity. Because artificial gravity systems increase the spacecraft’s size, mass and complexity, continuous gravity would be hard to accomplish. A more likely solution would be using intermittent artificial gravity before landing to reintroduce gravitational stimuli. Another option would be intermittent centrifugation of the body, using an off-axis rotator, or short-axis centrifuge. Such a countermeasure could be useful not only for the vestibular system (by creating simulated G forces), but also for the cardiovascular and musculoskeletal system.
The Astro-Omics approach to this situation would involve a careful analysis of the candidates for the mission. Testing would screen out those with vestibular systems completely unable to adapt to the space environment, and screen in those with extremely adaptable vestibular systems (this is not to say that those with minor vestibular issues would be overlooked as candidates). Such adaptability would decrease adaptation time and increase team effectiveness.