Space adaptation syndrome (SAS) or space sickness is a condition experienced by as many as half of all space travelers during their adaptation to weightlessness once in orbit. It is the opposite of terrestrial motion sickness since it occurs when the environment and the person appear visually to be in motion relative to one another even though there is no corresponding sensation of bodily movement originating from the vestibular system.
Presentation
Space motion sickness can lead to degraded astronaut performance. SMS threatens operational requirements, reduces situational awareness, and threatens the safety of those exposed to micro-g environments. Lost muscle mass leads to difficulty with movement, especially when astronauts return to Earth. This can pose a safety issue if the need for emergency egress were to arise. Loss of muscle power makes it extremely difficult, if not impossible, for astronauts to climb through emergency egress hatches or create unconventional exit spaces in the case of a crash upon landing. Additionally, bone resorption and inadequate hydration in space can lead to the formation of kidney stones, and subsequent sudden incapacitation due to pain. If this were to occur during critical phases of flight, a capsule crash leading to worker injury and/or death could result. Short-term and long-term health effects have been seen in the cardiovascular system from exposure to the micro-g environment that would limit those exposed after they return to Earth or a regular gravity environment. Steps need to be taken to ensure proper precautions are taken into consideration when dealing a micro-g environment for worker safety. Orthostatic intolerance can lead to temporary loss of consciousness due to the lack of pressure and stroke volume. This loss of consciousness inhibits and endangers those affected and can lead to deadly consequences.
Cause
When the vestibular system and the visual system report incongruous states of motion, the result is often nausea and other symptoms of disorientation known as motion sickness. According to contemporary sensory conflict theory, such conditions happen when the vestibular system and the visual system do not present a synchronized and unified representation of one's body and surroundings. This theory is also known as neural mismatch, implying a mismatch occurring between ongoing sensory experience and long-term memory rather than between components of the vestibular and visual systems, emphasizing "the limbic system in integration of sensory information and long-term memory, in the expression of the symptoms of motion sickness, and the impact of anti-motion-sickness drugs and stress hormones on limbic system function. The limbic system may be the neural mismatch center of the brain." At present a "fully adequate theory of motion sickness is not presently available" but at present the sensory conflict theory, referring to "a discontinuity between either visual, proprioceptive, and somatosensory input, or semicircular canal and otolith input", may be the best available.
Space adaptation syndrome or space sickness is a kind of motion sickness that can occur when one's surroundings visually appear to be in motion, but without a corresponding sense of bodily motion. This incongruous condition can occur during space travel when changes in g-forces compromise one's spatial orientation.
Garn's purpose on the mission was in part to subject him to experiments on space motion sickness. Predicting whether someone will experience space sickness is not possible. Someone who suffers from car sickness may not suffer from space sickness, and vice versa. In excellent physical condition, Garn did not become sick on the vomit comet before STS-51-D. All three astronauts on Skylab 3 suffered from nausea, although the three on Skylab 2 had not; the illness affected their work during the first few days, worrying NASA doctors.
Experienced aviators and space travelers can suffer from space sickness. Garn began piloting at the age of 16 and piloted a variety of military aircraft for 17,000 hours—more than any NASA astronaut—before STS-51-D. Charles D. Walker became ill on the same flight despite having flown on the shuttle before. While the Skylab 3 crew quickly recovered—whether by eating six smaller meals instead of three larger ones, or just by becoming used to space—one of the Skylab 4 crew became sick despite anti-nausea medication. Steven Smith estimated that on four shuttle flights he threw up 100 times.
Space sickness that occurs during space flight can also continue for days after landing, until the vestibular system has again adapted to gravity.
History
In August 1961, Soviet cosmonaut Gherman Titov became the first human to experience space sickness on Vostok 2; he was the first person to vomit in space.
Apart from that record, space motion sickness was effectively unknown during the earliest spaceflights (Mercury, Gemini series) probably because these missions were undertaken in spacecraft providing very cramped conditions and permitting very little room for head movements; space sickness seems to be aggravated by being able to freely move around, especially in regard to head movement, and so is more common in larger spacecraft.