effect of spaceflight on the human body effect of spaceflight on the human body venturing into the environment of space can have negative effects on the human body. significant adverse effects of long-term weightlessness include muscle atrophy and deterioration of the skeleton (spaceflight osteopenia). other significant effects include a slowing of cardiovascular system functions, decreased production of red blood cells (space anemia), balance disorders, eyesight disorders and changes in the immune system. additional symptoms include fluid redistribution (causing the "moon-face" appearance typical in pictures of astronauts experiencing weightlessness), loss of body mass, nasal congestion, sleep disturbance, and excess flatulence. overall, nasa refers to the various deleterious effects of spaceflight on the human body by the acronym ridge (i.e., "space radiation, isolation and confinement, distance from earth, gravity fields, and hostile and closed environments"). american astronaut marsha ivins demonstrates the effects of microgravity on her hair in space the engineering problems associated with leaving earth and developing space propulsion systems have been examined for over a century, and millions of hours of research have been spent on them. in recent years there has been an increase in research on the issue of how humans can survive and work in space for extended and possibly indefinite periods of time. this question requires input from the physical and biological sciences and has now become the greatest challenge (other than funding) facing human space exploration. a fundamental step in overcoming this challenge is trying to understand the effects and impact of long-term space travel on the human body. in october 2015, the nasa office of inspector general issued a health hazards report related to space exploration, including a human mission to mars. on 12 april 2019, nasa reported medical results, from the astronaut twin study, where one astronaut twin spent a year in space on the international space station, while the other twin spent the year on earth, which demonstrated several long-lasting changes, including those related to alterations in dna and cognition, when one twin was compared with the other. in november 2019, researchers reported that astronauts experienced serious blood flow and clot problems while on board the international space station, based on a six-month study of 11 healthy astronauts. the results may influence long-term spaceflight, including a mission to the planet mars, according to the researchers. physiological effects many of the environmental conditions experienced by humans during spaceflight are very different from those in which humans evolved; however, technology such as that offered by a spaceship or spacesuit is able to shield people from the harshest conditions. the immediate needs for breathable air and drinkable water are addressed by a life support system, a group of devices that allow human beings to survive in outer space. the life support system supplies air, water and food. it must also maintain temperature and pressure within acceptable limits and deal with the body's waste products. shielding against harmful external influences such as radiation and micro-meteorites is also necessary. some hazards are difficult to mitigate, such as weightlessness, also defined as a microgravity environment. living in this type of environment impacts the body in three important ways: loss of proprioception, changes in fluid distribution, and deterioration of the musculoskeletal system. on november 2, 2017, scientists reported that significant changes in the position and structure of the brain have been found in astronauts who have taken trips in space, based on mri studies. astronauts who took longer space trips were associated with greater brain changes. in october 2018, nasa-funded researchers found that lengthy journeys into outer space, including travel to the planet mars, may substantially damage the gastrointestinal tissues of astronauts. the studies support earlier work that found such journeys could significantly damage the brains of astronauts, and age them prematurely. in march 2019, nasa reported that latent viruses in humans may be activated during space missions, adding possibly more risk to astronauts in future deep-space missions. research main article: space medicine space medicine is a developing medical practice that studies the health of astronauts living in outer space. the main purpose of this academic pursuit is to discover how well and for how long people can survive the extreme conditions in space, and how fast they can re-adapt to the earth's environment after returning from space. space medicine also seeks to develop preventive and palliative measures to ease the suffering caused by living in an environment to which humans are not well adapted. ascent and re-entry during takeoff and re-entry space travelers can experience several times normal gravity. an untrained person can usually withstand about 3g, but can black out at 4 to 6g. g-force in the vertical direction is more difficult to tolerate than a force perpendicular to the spine because blood flows away from the brain and eyes. first the person experiences a temporary loss of vision and then at higher g-forces loses consciousness. g-force training and a g-suit which constricts the body to keep more blood in the head can mitigate the effects. most spacecraft are designed to keep g-forces within comfortable limits. space environments the environment of space is lethal without appropriate protection: the greatest threat in the vacuum of space derives from the lack of oxygen and pressure, although temperature and radiation also pose risks. the effects of space exposure can result in ebullism, hypoxia, hypocapnia, and decompression sickness. in addition to these, there is also cellular mutation and destruction from high energy photons and sub-atomic particles that are present in the surroundings. decompression is a serious concern during the extra-vehicular activities (evas) of astronauts. current extravehicular mobility unit (emu) designs take this and other issues into consideration, and have evolved over time. a key challenge has been the competing interests of increasing astronaut mobility (which is reduced by high-pressure emus, analogous to the difficulty of deforming an inflated balloon relative to a deflated one) and minimising decompression risk. investigators have considered pressurizing a separate head unit to the regular 71 kpa (10.3 psi) cabin pressure as opposed to the current whole-emu pressure of 29.6 kpa (4.3 psi). in such a design, pressurization of the torso could be achieved mechanically, avoiding mobility reduction associated with pneumatic pressurization. vacuum this 1768 painting, an experiment on a bird in the air pump by joseph wright of derby, depicts an experiment performed by robert boyle in 1660 to test the effect of a vacuum on a living system. human physiology is adapted to living within the atmosphere of earth, and a certain amount of oxygen is required in the air we breathe. if the body does not get enough oxygen, then the astronaut is at risk of becoming unconscious and dying from hypoxia. in the vacuum of space, gas exchange in the lungs continues as normal but results in the removal of all gases, including oxygen, from the bloodstream. after 9 to 12 seconds, the deoxygenated blood reaches the brain, and it results in the loss of consciousness. exposure to vacuum for up to 30 seconds is unlikely to cause permanent physical damage. animal experiments show that rapid and complete recovery is normal for exposures shorter than 90 seconds, while longer full-body exposures are fatal and resuscitation has never been successful. there is only a limited amount of data available from human accidents, but it is consistent with animal data. limbs may be exposed for much longer if breathing is not impaired. in december 1966, aerospace engineer and test subject jim leblanc of nasa was participating in a test to see how well a pressurized space suit prototype would perform in vacuum conditions. to simulate the effects of space, nasa constructed a massive vacuum chamber from which all air could be pumped. at some point during the test, leblanc's pressurization hose became detached from the space suit. even though this caused his suit pressure to drop from 3.8 psi (26.2 kpa) to 0.1 psi (0.7 kpa) in less than 10 seconds, leblanc remained conscious for about 14 seconds before losing consciousness due to hypoxia; the much lower pressure outside the body causes rapid de-oxygenation of the blood. "as i stumbled backwards, i could feel the saliva on my tongue starting to bubble just before i went unconscious and that's the last thing i remember", recalls leblanc. a colleague entered the chamber within 25 seconds and gave leblanc oxygen. the chamber was repressurized in 1 minute instead of the normal 30 minutes. leblanc recovered almost immediately with just an earache and no permanent damage. another effect from a vacuum is a condition called ebullism which results from the formation of bubbles in body fluids due to reduced ambient pressure, the steam may bloat the body to twice its normal size and slow circulation, but tissues are elastic and porous enough to prevent rupture. technically, ebullism is considered to begin at an elevation of around 19 kilometres (12 mi) or pressures less than 6.3 kpa (47 mm hg), known as the armstrong limit. experiments with other animals have revealed an array of symptoms that could also apply to humans. the least severe of these is the freezing of bodily secretions due to evaporative cooling. severe symptoms, such as loss of oxygen in tissue, followed by circulatory failure and flaccid paralysis would occur in about 30 seconds. the lungs also collapse in this process, but will continue to release water vapour leading to cooling and ice formation in the respiratory tract. a rough estimate is that a human will have about 90 seconds to be recompressed, after which death may be unavoidable. swelling from ebullism can be reduced by containment in a flight suit which are necessary to prevent ebullism above 19 km. during the space shuttle program astronauts wore a fitted elastic garment called a crew altitude protection suit (caps) which prevented ebullism at pressures as low as 2 kpa (15 mm hg). the only humans known to have died of exposure to vacuum in space are the three crew-members of the soyuz 11 spacecraft; vladislav volkov, georgi dobrovolski, and viktor patsayev. during preparations for re-entry from orbit on june 30, 1971, a pressure-equalisation valve in the spacecraft's descent module unexpectedly opened at an altitude of 168 kilometres (551,000 ft), causing rapid depressurisation and the subsequent death of the entire crew. temperature 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 temperature of a 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. rapid evaporative cooling of skin moisture in a vacuum may create frost, particularly in the mouth, but this is not a significant hazard. exposure to the intense radiation of direct, unfiltered sunlight would lead to local heating, though that would likely be well distributed by the body's conductivity and blood circulation. other solar radiation, particularly ultraviolet rays, however, may cause severe sunburn. radiation main article: health threat from cosmic rays comparison of radiation doses – includes the amount detected on the trip from earth to mars by the rad on the msl (2011–2013). without the protection of earth's atmosphere and magnetosphere astronauts are exposed to high levels of radiation. high levels of radiation damage lymphocytes, cells heavily involved in maintaining the immune system; this damage contributes to the lowered immunity experienced by astronauts. radiation has also recently been linked to a higher incidence of cataracts in astronauts. outside the protection of low earth orbit, galactic cosmic rays present further challenges to human spaceflight, as the health threat from cosmic rays significantly increases the chances of cancer over a decade or more of exposure. a nasa-supported study reported that radiation may harm the brain of astronauts and accelerate the onset of alzheimer's disease. solar flare events (though rare) can give a fatal radiation dose in minutes. it is thought that protective shielding and protective drugs may ultimately lower the risks to an acceptable level. crew living on the international space station (iss) are partially protected from the space environment by earth's magnetic field, as the magnetosphere deflects solar wind around the earth and the iss. nevertheless, solar flares are powerful enough to warp and penetrate the magnetic defences, and so are still a hazard to the crew. the