Space adaptation syndrome
Space sickness affects up to half of space travelers during weightlessness adaptation.
Space adaptation syndrome (SAS), or space sickness, affects up to half of everyone who travels into orbit as their bodies adjust to weightlessness. Unlike motion sickness on Earth, it happens when what a person sees appears to be moving relative to their surroundings, yet their vestibular system reports no corresponding physical motion.
The condition can seriously impair an astronaut’s performance. It interferes with mission tasks, reduces awareness of one’s surroundings, and endangers safety in microgravity. Lost muscle mass makes movement difficult, especially after returning to Earth, and could become a safety hazard if an emergency exit is needed—climbing through hatches or creating escape routes after a crash landing may become impossible. Bone loss and poor hydration in space raise the risk of kidney stones, which can cause sudden, incapacitating pain. If that occurs during a critical phase of flight, it could lead to a capsule crash and injuries or death. Short- and long-term cardiovascular effects from microgravity also limit what astronauts can do once back in a normal gravity environment. Proper precautions are essential for worker safety in microgravity. Orthostatic intolerance—a drop in blood pressure and stroke volume—can cause temporary loss of consciousness, which endangers those affected and could be deadly.
The human body simply isn’t built for zero gravity, and there is no way to predict how an individual will react. Someone prone to car sickness might be fine in space, or the opposite. The cause lies in a mismatch between the vestibular system and the visual system. When these systems report conflicting states of motion, nausea and disorientation—motion sickness—often result. The leading explanation, sensory conflict theory (also called neural mismatch), holds that this mismatch occurs between ongoing sensory input and long-term memory, rather than just between the vestibular and visual systems. It emphasizes the limbic system’s role in integrating sensory information and memory, expressing symptoms, and responding to anti-motion-sickness drugs and stress hormones. The limbic system may be the brain’s neural mismatch center. No fully adequate theory of motion sickness exists yet, but sensory conflict—a discontinuity between visual, proprioceptive, somatosensory, or semicircular canal and otolith input—is currently the best available.
Quick Facts
- Causes
- <!-- or
- Prevalence
- 50% of individuals
Facts from the source article.
Lore & Background
Space adaptation syndrome 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. According to sensory conflict theory, this happens when the vestibular system and the visual system do not present a synchronized and unified representation of one's body and surroundings, also known as neural mismatch. The limbic system may be the neural mismatch center of the brain, though a fully adequate theory of motion sickness is not presently available. Sleep deprivation can increase susceptibility to space sickness, making symptoms worse and longer-lasting.
Symptoms can vary from mild nausea and disorientation to vomiting and intense discomfort; headaches and nausea are often reported in varying degrees. The most extreme reaction recorded was that felt by Senator Jake Garn in 1985 on Space Shuttle flight STS-51-D, leading to the informal 'Garn scale' to measure reactions. Experienced aviators and space travelers can suffer from space sickness; Garn began piloting at age 16 and piloted military aircraft for 17,000 hours, yet became severely ill. Charles D. Walker became ill on the same flight despite having flown on the shuttle before, and 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. 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. All three astronauts on Skylab 3 suffered from nausea, although the three on Skylab 2 had not, and the illness affected their work during the first few days.
Reader's Guide
Space adaptation syndrome is significant because it can lead to degraded astronaut performance, threatening operational requirements, reducing situational awareness, and threatening the safety of those exposed to micro-g environments. Lost muscle mass leads to difficulty with movement, especially when astronauts return to Earth, posing a safety issue if emergency egress were needed. Bone resorption and inadequate hydration can lead to kidney stones and sudden incapacitation due to pain, which could cause a capsule crash during critical phases of flight. Orthostatic intolerance can lead to temporary loss of consciousness, endangering those affected with potentially deadly consequences. Short-term and long-term health effects have been seen in the cardiovascular system from micro-g exposure, limiting those exposed after they return to a regular gravity environment.
Management involves restricting vision to a small area such as a book or small screen, or closing one's eyes until the nauseated feeling is reduced during the adjustment period. Contemporary motion sickness medications can counter space sickness by temporarily suppressing the vestibular system, but are rarely used for space travel because it is considered better to allow natural adaptation over the first one to seven days rather than suffer drowsiness and other side effects. However, transdermal dimenhydrinate anti-nausea patches are typically used whenever space suits are worn because vomiting into a space suit could be fatal by obscuring vision or blocking airflow. Extra-vehicular activities are consequently not usually scheduled for the first days of a mission to allow the crew to adapt, with transdermal dimenhydrinate patches used as an additional backup measure.
Did You Know?
- Space adaptation syndrome is the opposite of terrestrial motion sickness: in space, surroundings appear to move while the body feels still.
- The informal 'Garn scale' measures space sickness severity, named after Senator Jake Garn who experienced the most extreme reaction on STS-51-D.
- Transdermal dimenhydrinate patches are used when space suits are worn because vomiting into a suit could be fatal by obscuring vision or blocking airflow.
- Experienced aviators with thousands of flight hours, such as Senator Jake Garn (17,000 hours), can still suffer severe space sickness.
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