Human physiological adaptation to the conditions of space is a challenge faced in the development of human spaceflight. Layers of Atmosphere - not to scale (NOAA)[1] Outer space, sometimes simply called space, refers to the relatively empty regions of the universe outside the atmospheres of celestial bodies. ... Edward White on a spacewalk during the Gemini 4 mission. ...

The fundamental engineering problems of escaping Earth's gravity well and developing systems for in-space propulsion have been examined for well over a century, and millions of man-hours of research have been spent on them. In recent years there has been an increase in research into the issue of how humans can actually stay in space and will actually survive and work in space for long periods of time. This question requires input from the whole gamut of physical and biological sciences and has now become the greatest challenge, other than funding, to human space exploration. A fundamental step in overcoming this challenge is trying to understand the effects and the impact long space travel has on the human body. This article is about Earth as a planet. ... Gravity is a force of attraction that acts between bodies that have mass. ... A remote camera captures a close-up view of a Space Shuttle Main Engine during a test firing at the John C. Stennis Space Center in Hancock County, Mississippi Spacecraft propulsion is used to change the velocity of spacecraft and artificial satellites, or in short, to provide delta-v. ... Space exploration is the physical exploration of outer space, both by human spaceflights and by robotic spacecraft. ...

Importance of subject

Space colonization efforts must take into account the effects of space on the body

The sum of mankind's experience has resulted in the accumulation of 58 man-years in space and a much better understanding of how the human body adapts. However, in the future, industrialisation of space and exploration of inner and outer planets will require humans to endure longer and longer periods in space. A recent report has highlighted the limits to the quality and quantity of current data, which make it difficult for scientists to extrapolate all the effects of living in space long term.^{[citation needed]} The majority of the data comes from missions of short duration and so some of the long-term physiological effects of living in space are still unknown. A round trip to Mars with current technology is estimated to involve at least 18 months in transit alone. How the human body reacts to such time periods in space is a vital part of the preparation for such journeys. On-board medical facilities need to be able to cope with any type of trauma or emergency as well as contain a huge variety of diagnostic and medical instruments in order to keep a crew healthy over a long period of time, as these will be the only facilities available on board a spacecraft to cope with not only trauma, but also the adaptive responses of the human body in space. Image File history File links Download high-resolution version (1800x1404, 1161 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Stanford torus Human adaptation to space User talk:Exodio Wikipedia talk:WikiProject Space Colonization Template:WPSpaceColonization User:Zakpaz... Image File history File links Download high-resolution version (1800x1404, 1161 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Stanford torus Human adaptation to space User talk:Exodio Wikipedia talk:WikiProject Space Colonization Template:WPSpaceColonization User:Zakpaz... Space manufacturing is the production of manufactured goods in an environment outside a planetary atmosphere. ... Artists conception of a space habitat called the Stanford torus, by Don Davis Space colonization (also called space settlement, space humanization, space habitation, etc. ... Adjectives: Martian Atmosphere Surface pressure: 0. ...

Public perception of issues

Public perception of living in space is generally skewed towards the TV sci-fi of Star Trek where gravity is artificially produced and journeys to distant stars take less than a day.^[1] The real-world difficulties of extended space travel are far more complex than those presented in most science fiction novels or movies. TV redirects here. ... Science fiction is a form of speculative fiction principally dealing with the impact of imagined science and technology, or both, upon society and persons as individuals. ... This article is about the entire Star Trek franchise. ...

Effects on humans

The effects of space conditions on humans can be separated into two areas, the physical and the psychological.

Unprotected effects

See also: Explosive decompression and Space exposure

The environment of space is highly dangerous without appropriate protection. The greatest threat is from the lack of pressure in the vacuum environment, while temperature and radiation effects also have an influence. Explosive decompression (ED) is a sudden drop in pressure that occurs in 0. ... Space exposure is in reference to the exposure of a human, without protective clothing and beyond the Earth’s atmosphere in a vacuum. ...

Contrary to imagery in the public media (as in such films as Outland, Total Recall, and Event Horizon), a short term exposure to vacuum of up to 30 seconds is unlikely to cause permanent physical damage.^[2] Outland is a 1981 science fiction movie starring Sean Connery. ... For other uses, see Total recall (disambiguation). ... Event Horizon is a 1997 science fiction horror film that was directed by Paul W. S. Anderson and written by Philip Eisner (with an uncredited rewrite by Andrew Kevin Walker). ...

Gases in the body will expand. If the victim attempts to hold his breath then the expanding air in the lungs will be unable to escape and will inflate the lungs to the point of rupturing them. Perforated eardrums may result if pressure cannot be equalized fast enough (similar to the problems that occur in scuba diving). The gastric system also contains a certain amount of gas, and that will expand as well.

Liquids inside the body - including water - will not boil. At body temperature the vapour pressure of water is 47mm Hg,^[3] or 1/16 of normal atmospheric pressure. Skin is a very strong substance well able to exert a much higher pressure on expanding body contents. Exposed liquids will boil (see the reference to saliva, below).

Dissolved gases in the blood may come out of solution, and after 10 seconds or so, decompression sickness (the bends) may result. Decompression sickness (DCS), the diver’s disease, the bends, or caisson disease is the name given to a variety of symptoms suffered by a person exposed to a decrease (nearly always after a big increase) in the pressure around his body. ...

In a vacuum there is no medium for removing heat from the body by conduction or convection. Loss of heat is by radiation from the 310 K person to the 3 K of outer space. This is a slow process, especially in a clothed person, so there is no danger of immediately freezing. (Evaporation of skin moisture in the vacuum would cause immediate cooling but only by a very small amount).

Exposure to the 6000 K radiation from the sun would lead to local heating that would be well distributed by the body's conductivity and blood circulation. Other solar radiation, particularly ultraviolet rays may cause severe sunburn in a few seconds. For other uses, see Radiation (disambiguation). ... For other uses, see Ultraviolet (disambiguation). ...

However, the primary threat is of asphyxiation. In the low pressure environment, gas exchange in the lungs would continue as normal but would result in the removal of all gases, including oxygen, from the bloodstream. After up to 15 seconds, the deoxygenated blood would reach the brain, and loss of consciousness would result. Death would gradually follow after two minutes of exposure - though the limits are uncertain. If actions are taken quickly, and normal pressure restored within around 90 seconds, the victim may well make a full recovery. ^[4] Asphyxia is a condition of severely deficient supply of oxygen to the body. ...

As well as experimentation with humans and monkeys, a few cases of loss of pressure have occurred in the past, especially in experimentation on spaceflight projects. One such case is discussed in a NASA technical report: Rapid (Explosive) Decompression Emergencies in Pressure-Suited Subjects: NASA Logo Listen to this article · (info) This audio file was created from the revision dated 2005-09-01, and does not reflect subsequent edits to the article. ...

"At NASA's Manned Spacecraft Center (now renamed Johnson Space Center) we had a test subject accidentally exposed to a near vacuum (less than 1 psi) [7 kPa] in an incident involving a leaking space suit in a vacuum chamber back in '65. He remained conscious for about 14 seconds, which is about the time it takes for O₂ deprived blood to go from the lungs to the brain. The suit probably did not reach a hard vacuum, and we began repressurizing the chamber within 15 seconds. The subject regained consciousness at around 15,000 feet [4600 m] equivalent altitude. The subject later reported that he could feel and hear the air leaking out, and his last conscious memory was of the water on his tongue beginning to boil."

There has been one recorded incident of death from decompression in spaceflight, the Soyuz 11 decompression accident, in 1971. An aerial view of the complete Johnson Space Center facility in Houston, Texas in 1989. ... Pounds-force per square inch (lbf/in²) is a non-SI unit of pressure. ... The pascal (symbol Pa) is the SI unit of pressure. ... Year 1965 (MCMLXV) was a common year starting on Friday (link will display full calendar) of the 1965 Gregorian calendar. ... This article is about the unit of length. ... Soyuz 11 was the first successful visit to the worlds first space station, Salyut 1, but ended in disaster when an air leak killed the three-man crew during preparations for re-entry. ...

See also: Spacesuit and Vacuum

• External link: Human Exposure to Vacuum

Apollo 15 space suit A spacesuit is a complex system of garments, equipment, and environmental systems designed to keep a person alive and comfortable in the harsh environment of outer space. ... Look up Vacuum in Wiktionary, the free dictionary. ...

Protected effects

See also: Space adaptation syndrome

Despite modern technology, some hazards still prove impossible to remove. The most important factor affecting human physical well being in space is weightlessness, more accurately defined as microgravity environments. Living in this type of environment impacts on 3 types of human tissue: Space adaptation syndrome, or space sickness, is what astronauts go through during adaptation to zero gravity. ... Astronauts on the International Space Station display an example of weightlessness Weightlessness is the experience (by people and objects) during freefall, of having no weight. ...

• gravity receptors
• fluids
• weight bearing structures

Gravity receptors

Main article: Spacesickness

2001: A Space Odyssey boasted an unusually realistic portrayal of spaceflight, including a centrifuge-like living chamber to generate artificial gravity

Living on earth we constantly feel the gravitational pull and our bodies react automatically to maintain posture and locomotion in a downward pulling world. In microgravity environments, these constant signals the body is adapted to are absent. The otolith organs in the middle ear sensitive to linear accelerations no longer perceive a downwards bias, muscles are no longer required to contract to maintain posture and pressure receptors in the feet and ankles no longer signal the direction of down. These changes can immediately result in visual-orientation illusions where the astronaut feels he has flipped 180 degrees. Over time however the brain adapts and although these illusions can still occur most astronauts begin to see "down" as where the feet are. People returning to Earth after extended weightless periods initially have great difficulty maintaining their balance but recover the ability very quickly, highlighting the remarkable ability of the human body to adapt. Over half of astronauts also experience symptoms of motion sickness for the first three days of travel due to the conflict between what the body expects and what the body actually perceives.^[5] This article or section does not cite its references or sources. ... The control room in Discovery in 2001: A Space Odyssey. ... The control room in Discovery in 2001: A Space Odyssey. ... An otolith, (oto-, ear + lithos, a stone), also called statoconium[1] or otoconium is a structure in the saccule or utricle of the inner ear, specifically in the vestibular labyrinth. ... For other uses, see Ear (disambiguation). ... Motion sickness or kinetosis is a condition in which a disagreement exists between visually perceived movement and the vestibular systems sense of movement. ...

Fluids

The second effect of weightlessness takes place in human fluids. The body is made up of 60% water, much of it intra-vascular and inter-cellular. Within a few moments of entering a microgravity environment, fluid is immediately re-distributed to the upper body resulting in bulging neck veins, puffy face and sinus and nasal congestion which can last throughout the duration of the trip and is very much like the symptoms of the common cold. In space the autonomic reactions of the body to maintain blood pressure are not required and fluid is distributed more widely around the whole body. This results in a decrease in plasma (water in the blood stream) volume of around 20%. These fluid shifts initiate a cascade of adaptive systemic effects that can be dangerous upon return to earth. Orthostatic intolerance results in astronauts returning to Earth after extended space missions being unable to stand unassisted for more than 10 minutes at a time without fainting. This is due in part to changes in the autonomic regulation of blood pressure and the loss of plasma volume. Although this effect becomes worse the longer the time spent in space, as yet all individuals have returned to normal within at most a few weeks of landing.^{[citation needed]} Blood plasma is the liquid component of blood, in which the blood cells are suspended. ... Orthostatic intolerance is the failure of the body to properly adjust to an upright position, especially with respect to blood flow, heart rate, and blood pressure. ...

Weight bearing structures

The third and most worrying effect of long-term weightlessness involves bones and muscles. Without the effects of gravity, skeletal muscle is no longer required to maintain our posture and the muscle groups used in moving around in a weightless environment are very different to those required in terrestrial locomotion.^{[citation needed]} Consequently some muscles atrophy rapidly. The types of muscle fibre prominent in muscles also change. Slow twitch endurance fibres used to maintain posture are replaced by fast twitch rapidly contracting fibres that are insufficient for any heavy labour. Bone metabolism also changes. Normally bone is laid down in the direction of mechanical stress, however in a microgravity environment there is very little mechanical stress. This results in a loss of bone tissue approximately 1.5% per month especially from the lower vertebrae, hip and femur. Elevated blood calcium levels from the lost bone result in dangerous calcification of soft tissues and potential kidney stone formation. It is still unknown whether bone recovers completely. Loss of bone and muscle make it very difficult for humans to move and even breathe under the weight of Earth's pull upon their return. The longer the flight, the more loss will occur until it may become impossible for the individual to survive the pull of Earth's gravity for any extended period of time.^{[citation needed]} This article is about the skeletal organs. ... For other uses of Muscles, see Muscles (disambiguation). ... A top-down view of skeletal muscle Skeletal muscle is a type of striated muscle, usually attached to the skeleton. ... A muscle fiber (American usage) or muscle fibre (British usage) is a single cell of a muscle. ... This article is about the skeletal organs. ... For other uses, see Calcium (disambiguation). ... “Bladder stone” redirects here. ...

Effects of radiation

Weightlessness is not the only factor to affect the human body in space. Without the protection of the Earth's atmosphere and magnetosphere astronauts are exposed to high levels of radiation through a steady flux of cosmic rays. A year in even low-earth orbit results in a dose of radiation 10 times that of the annual dose on earth resulting in a high risk of astronauts developing cancer. High levels of radiation can create 'chromosomal aberrations' in blood lymphocytes. These cells are heavily involved in the immune system and so any damage may contribute to the lowered immunity experienced by astronauts. Over time immunodeficiency results in the rapid spread of infection between crewmembers, especially in such confined areas. Radiation has also recently been linked to a higher incidence of cataracts in astronauts. Protective shielding and protective drugs may lower the risks to astronauts to an acceptable level, but data is scarce and longer-term exposure will result in greater risks.^{[citation needed]} A magnetosphere is the region around an astronomical object in which phenomena are dominated or organized by its magnetic field. ... For other uses, see Radiation (disambiguation). ... Cosmic rays can loosely be defined as energetic particles originating outside of the Earth. ... This article is about the biological chromosome. ... A lymphocyte is a type of white blood cell involved in the human bodys immune system. ... A scanning electron microscope image of a single neutrophil (yellow), engulfing anthrax bacteria (orange). ... Immunity is a medical term that describes a state of having sufficient biological defenses to avoid infection, disease, or other unwanted biological invasion. ... Cataract is also used to mean a waterfall or where the flow of a river changes dramatically. ...

Sense of taste

One effect of weightlessness on humans is that some astronauts report a change in their sense of taste in space^[6]. Some astronauts find that their food is bland, others find that their favorite foods no longer tastes as good, some astronauts enjoy eating certain foods that they would not normally eat and some find no change whatsoever. The reason for this is uncertain, and several theories have been suggested:

• Congestion - Microgravity may cause fluid buildup in the sinuses, changing the taste in a similar fashion to holding one's nose while eating.
• Physical food degradation - Food in orbit is often stored for some months before being consumed. This and the stellar radiation may cause a breakdown in the groups of chemicals that give food its taste, resulting in bland food.
• Boredom - Menus for the ISS astronauts are planned on a repeating 8-day cycle, which are selected from a menu designed by NASA, and taken into space with the astronaut. This constant repetition may lead to some astronauts getting tired of food that they had previously liked.
• Psychological changes - The loss of taste may be purely psychological.

Astronauts often choose strongly tasting food such as salsa or shrimp cocktail. Nasal congestion is the blockage of the nasal passages usually due to membranes lining the nose becoming swollen from inflamed blood vessels. ... Note: This page or section contains IPA phonetic symbols in Unicode. ... Description An appetizer typically consisting of cooked, peeled, chilled shrimp or prawns and cocktail sauce. ...

Other physical effects

Much data on long-term effects derive from studies of Russian cosmonauts, such as on Mir.

Other physical discomforts such as back and abdominal pain are commonly experienced with no clear cause. These may be part of the asthenia syndrome reported by cosmonauts living in space over an extended period of time, but seen as anecdotal by astronauts.^{[citation needed]} Fatigue, listlessness, and psychosomatic worries are also part of the syndrome. Data is inconclusive, however the syndrome does appear to exist as a manifestation of all the internal and external stress crews in space must face. The amount and quality of sleep experienced in space is poor due to highly variable light and dark cycles on flight decks and poor illumination during daytime hours in the space craft. Even the habit of looking out of the window before retiring can send the wrong messages to the brain resulting in poor sleep patterns. These disturbances in circadian rhythm have profound effects on the neurobehavioral responses of crew and aggravate the psychological stresses they already experience.^{[citation needed]} Download high resolution version (639x601, 263 KB) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Download high resolution version (639x601, 263 KB) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... For other uses, see Mir (disambiguation). ... Asthenia (Greek: ασθένεια, lit. ... U.S. Space Shuttle astronaut Bruce McCandless II using a manned maneuvering unit. ... For other uses, see Sleep (disambiguation). ... A circadian rhythm is a roughly-24-hour cycle in the physiological processes of living beings, including plants, animals, fungi and cyanobacteria. ...

It has been reported that on returning to Earth from space, some subjects continue with conduct that suits the zero-gravity environment of space for example, throwing objects like pencils to another person as one would do in zero gravity, only for it to drop on the floor with the effect of gravity on Earth.

Psychological effects

The psychological effects of living in space have not been clearly analyzed but analogies on Earth do exist, such as Arctic research stations and submarines. The enormous stress on the crew, coupled with the body adapting to other environmental changes, can result in anxiety, insomnia and depression. According to current data^{[citation needed]} however astronauts and cosmonauts seem extremely resilient to psychological stresses. Interpersonal issues can have an enormous influence on a human's well being and yet little research has been undertaken to examine crew selection issues in relation to this. The Mars Arctic Research Station and Mars Desert Research Station have examined the influence of different crew selections when living in a completely isolated environment and may provide vital data for future experiences.^{[citation needed]} The red line indicates the 10°C isotherm in July, commonly used to define the Arctic region border Artificially coloured topographical map of the Arctic region The Arctic is the region around the Earths North Pole, opposite the Antarctic region around the South Pole. ... For other uses, see Submarine (disambiguation). ...

Future prospects

At the moment only rigorously tested humans have experienced the conditions of space. If off-world colonization someday begins, many types of people will be exposed to these dangers, and the effects on the elderly and on the very young are completely unknown. Factors such as nutritional requirements and physical environments which have not been examined here will become important. Over all, there is little data on the manifold effects of living in space and this makes working to mitigate the risks during a lengthy space habitation difficult. Test beds such as the International Space Station (ISS) are presently being utilized to research some of these risks. Artists conception of a space habitat called the Stanford torus, by Don Davis Space colonization (also called space settlement, space humanization, space habitation, etc. ... A testbed is a platform for experimentation for large development projects. ... ISS redirects here. ...

The environment of space is still largely unknown, and there will be hazards of which we are not currently aware. Meanwhile, future technologies such as artificial gravity and more complex bioregenerative life support systems may someday be capable of mitigating some hazards. Artificial gravity is a simulation of gravity in outer space or free-fall. ... In human spaceflight, the life support system is a group of devices that allow a human being to survive in outer space. ...

See also

• Space colonization
• Space adaptation syndrome

Artists conception of a space habitat called the Stanford torus, by Don Davis Space colonization (also called space settlement, space humanization, space habitation, etc. ... Space adaptation syndrome, or space sickness, is what astronauts go through during adaptation to zero gravity. ...

References

Sources

1. Nasa Report: Space Travel 'Inherently Hazardous' to Human Health. Leonard David. 2001
2. Space Physiology and Medicine. Third edition. A. E. Nicogossian, C. L. Huntoon and S. L. Pool. Lea & Febiger, 1993.
3. L.-F. Zhang. Vascular adaptation to microgravity: What have we learned?. Journal of Applied Physiology. 91(6) (pp 2415-2430), 2001.
4. G. Carmeliet, Vico. L, Bouillon R. Critical Reviews in Eukaryotic Gene Expression. Vol 11(1-3) (pp 131-144), 2001.
5. F.A. Cucinotta et al Space radiation cancer risks and uncertainties for Mars missions. Radiation Research. Vol 156:5 II;pp 682-688, 2001.
6. F.A. Cucinotta et al. Space radiation and cataracts in astronauts. Radiation Research. Vol 156(5 I) (pp 460-466), 2001.
7. Styf, Jorma R. MD; Hutchinson, Karen BS; Carlsson, Sven G. PhD, and; Hargens, Alan R. Ph.D. Depression, Mood State, and Back Pain During