Space adaptation syndrome
Space adaptation syndrome (SAS) or space sickness is a condition experienced by around half of space travelers during adaptation to weightlessness
Weightlessness is the condition that exists for an object or person when they experience little or no acceleration except the acceleration that defines their inertial trajectory, or the trajectory of pure free-fall...

. It is related to motion sickness
Motion sickness
Motion sickness or kinetosis, also known as travel sickness, is a condition in which a disagreement exists between visually perceived movement and the vestibular system's sense of movement...

, as the vestibular system
Vestibular system
The vestibular system, which contributes to balance in most mammals and to the sense of spatial orientation, is the sensory system that provides the leading contribution about movement and sense of balance. Together with the cochlea, a part of the auditory system, it constitutes the labyrinth of...

 adapts to weightlessness.

Cause and remedy

Space sickness is caused by changes in g-force
The g-force associated with an object is its acceleration relative to free-fall. This acceleration experienced by an object is due to the vector sum of non-gravitational forces acting on an object free to move. The accelerations that are not produced by gravity are termed proper accelerations, and...

s, which affect spatial orientation in humans. According to Science Daily
Science Daily
Science Daily is a news website for topical science articles. It features articles on a wide variety of science topics including: astronomy, exoplanets, computer science, nanotechnology, medicine, psychology, sociology, anthropology, biology, geology, climate, space, physics, mathematics,...

, "Gravity plays a major role in our spatial orientation. Changes in gravitational forces, such as the transition to weightlessness during a space voyage, influence our spatial orientation and require adaptation by many of the physiological processes in which our balance system plays a part. As long as this adaptation is incomplete, this can be coupled to motion sickness (nausea), visual illusions and disorientation." One understanding of motion sickness is that nausea is a pro-survival evolutionary adaptation, because the sensory stimulation of a maladapted high acceleration environment that the body is not accustomed to is recognized by the brain as being similar to the sensory conflict from eating a poisonous plant, in which case vomiting is a helpful reaction.

Modern motion-sickness medications can counter space sickness but are rarely used because it is considered better to allow space travelers to adapt naturally over the first day or two than to suffer the drowsiness and other side effects of medication. However, transdermal
Transdermal patch
A transdermal patch is a medicated adhesive patch that is placed on the skin to deliver a specific dose of medication through the skin and into the bloodstream. Often, this promotes healing to an injured area of the body. An advantage of a transdermal drug delivery route over other types of...

Dimenhydrinate is an over-the-counter drug used to prevent nausea and motion sickness...

 anti-nausea patches are typically used whenever space suits are worn because vomiting into a space suit could be fatal. Space suits are generally worn during launch and landing by NASA crew members and always for extra-vehicular activities (EVAs). EVAs are consequently not usually scheduled for the first days of a mission to allow the crew to adapt, and transdermal dimenhydrinate patches are typically used as an additional backup measure.


Space sickness was effectively unknown during the earliest spaceflights as these were undertaken in very cramped conditions; it seems to be aggravated by being able to freely move around and so is more common in larger spacecraft. After the Apollo 8
Apollo 8
Apollo 8, the second manned mission in the American Apollo space program, was the first human spaceflight to leave Earth orbit; the first to be captured by and escape from the gravitational field of another celestial body; and the first crewed voyage to return to Earth from another celestial...

and Apollo 9
Apollo 9
Apollo 9, the third manned mission in the American Apollo space program, was the first flight of the Command/Service Module with the Lunar Module...

flights, where astronauts reportedly reported space sickness to Mission Control and then were subsequently removed from the flight list, astronauts (e.g. the Skylab 4 crew) attempted to prevent Mission Control from learning about their own SAS experience, apparently out of concern for their future flight assignment potential.

As with motion sickness, symptoms can vary from mild nausea and disorientation, to vomiting and intense discomfort; headaches and nausea are often reported in varying degrees. About half of sufferers experience mild symptoms; only around 10% suffer severely. The most extreme reaction yet recorded was that felt by Senator Jake Garn
Jake Garn
Edwin Jacob "Jake" Garn is an American politician, a member of the Republican Party, and served as a U.S. Senator representing Utah from 1974 to 1993...

 in 1985. After his flight NASA astronauts began using the informal "Garn scale" to measure reactions to space sickness. In most cases, symptoms last from 2–4 days. In an interview with Carol Butler, when asked about the origins of "Garn" Robert E. Stevenson was quoted as saying:

See also

  • Human adaptation to spaceflight
  • Human spaceflight
    Human spaceflight
    Human spaceflight is spaceflight with humans on the spacecraft. When a spacecraft is manned, it can be piloted directly, as opposed to machine or robotic space probes and remotely-controlled satellites....

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