Venturing into the environment of space can have negative effects on the human body.
Significant adverse effects of long-term
weightlessness
Weightlessness is the complete or near-complete absence of the sensation of weight. It is also termed zero gravity, zero G-force, or zero-G.
Weight is a measurement of the force on an object at rest in a relatively strong gravitational fi ...
include
muscle atrophy
Muscle atrophy is the loss of skeletal muscle mass. It can be caused by immobility, aging, malnutrition, medications, or a wide range of injuries or diseases that impact the musculoskeletal or nervous system. Muscle atrophy leads to muscle weakness ...
and deterioration of the
skeleton
A skeleton is the structural frame that supports the body of an animal. There are several types of skeletons, including the exoskeleton, which is the stable outer shell of an organism, the endoskeleton, which forms the support structure inside ...
(
spaceflight osteopenia
Spaceflight osteopenia refers to the characteristic bone loss that occurs during spaceflight. Astronauts lose an average of more than 1% bone mass per month spent in space. There is concern that during long-duration flights, excessive bone loss ...
).
Other significant effects include a slowing of
cardiovascular system
The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, tha ...
functions, decreased production of
red blood cell
Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek ''erythros'' for "red" and ''kytos'' for "holl ...
s (space anemia),
balance disorders
A balance disorder is a disturbance that causes an individual to feel unsteady, for example when standing or walking. It may be accompanied by feelings of giddiness, or wooziness, or having a sensation of movement, spinning, or floating. Balance ...
,
eyesight disorders and changes in the
immune system
The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splinte ...
.
Additional symptoms include
fluid redistribution (causing the "
moon-face" appearance typical in pictures of astronauts experiencing weightlessness),
loss of
body mass
Human body weight is a person's Mass versus weight, mass or weight.
Strictly speaking, body weight is the measurement of weight without items located on the person. Practically though, body weight may be measured with clothes on, but without shoe ...
,
nasal congestion
Nasal congestion is the blockage of nasal breathing usually due to membranes lining the nose becoming swollen from inflamed blood vessels.
Background
In about 85% of cases, nasal congestion leads to mouth breathing rather than nasal breathing. ...
,
sleep disturbance
A sleep disorder, or somnipathy, is a medical disorder of an individual's sleep patterns. Some sleep disorders are severe enough to interfere with normal physical, mental, social and emotional functioning. Polysomnography and actigraphy are test ...
, and excess
flatulence
Flatulence, in humans, is the expulsion of gas from the intestines via the anus, commonly referred to as farting. "Flatus" is the medical word for gas generated in the stomach or bowels. A proportion of intestinal gas may be swallowed environm ...
. 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").
The engineering problems associated with leaving
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
and developing
space propulsion
Spacecraft propulsion is any method used to accelerate spacecraft and artificial satellites. In-space propulsion exclusively deals with propulsion systems used in the vacuum of space and should not be confused with space launch or atmospheric e ...
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
Space exploration is the use of astronomy and space technology to explore outer space. While the exploration of space is carried out mainly by astronomers with telescopes, its physical exploration though is conducted both by robotic spacec ...
. 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
The NASA Office of Inspector General (NASA OIG or OIG) is the inspector general office in the National Aeronautics and Space Administration, the space agency of the United States. The OIG's stated mission is to "prevent and detect crime, fraud, wa ...
issued a health hazards report related to
space exploration
Space exploration is the use of astronomy and space technology to explore outer space. While the exploration of space is carried out mainly by astronomers with telescopes, its physical exploration though is conducted both by robotic spacec ...
, including a
human mission to Mars
The idea of sending humans to Mars has been the subject of aerospace engineering and scientific studies since the late 1940s as part of the broader exploration of Mars. Some have also considered exploring the Martian moons of Phobos and Deimos. ...
.
On 12 April 2019,
NASA
The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research.
NASA was established in 1958, succeeding t ...
reported medical results, from the
Astronaut Twin Study, where one
astronaut
An astronaut (from the Ancient Greek (), meaning 'star', and (), meaning 'sailor') is a person trained, equipped, and deployed by a human spaceflight program to serve as a commander or crew member aboard a spacecraft. Although generally r ...
twin
Twins are two offspring produced by the same pregnancy.MedicineNet > Definition of TwinLast Editorial Review: 19 June 2000 Twins can be either ''monozygotic'' ('identical'), meaning that they develop from one zygote, which splits and forms two em ...
spent a year in space on the
International Space Station
The International Space Station (ISS) is the largest modular space station currently in low Earth orbit. It is a multinational collaborative project involving five participating space agencies: NASA (United States), Roscosmos (Russia), JAXA ...
, while the other twin spent the year on
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
, which demonstrated several long-lasting changes, including those related to alterations in
DNA and
cognition
Cognition refers to "the mental action or process of acquiring knowledge and understanding through thought, experience, and the senses". It encompasses all aspects of intellectual functions and processes such as: perception, attention, thought, ...
, when one twin was compared with the other.
In November 2019, researchers reported that
astronaut
An astronaut (from the Ancient Greek (), meaning 'star', and (), meaning 'sailor') is a person trained, equipped, and deployed by a human spaceflight program to serve as a commander or crew member aboard a spacecraft. Although generally r ...
s experienced serious
blood flow
Hemodynamics or haemodynamics are the dynamics of blood flow. The circulatory system is controlled by homeostatic mechanisms of autoregulation, just as hydraulic circuits are controlled by control systems. The hemodynamic response continuously m ...
and
clot
A thrombus (plural thrombi), colloquially called a blood clot, is the final product of the blood coagulation step in hemostasis. There are two components to a thrombus: aggregated platelets and red blood cells that form a plug, and a mesh of cr ...
problems while on board the
International Space Station
The International Space Station (ISS) is the largest modular space station currently in low Earth orbit. It is a multinational collaborative project involving five participating space agencies: NASA (United States), Roscosmos (Russia), JAXA ...
, based on a six-month study of 11 healthy astronauts. The results may influence long-term
spaceflight
Spaceflight (or space flight) is an application of astronautics to fly spacecraft into or through outer space, either with or without humans on board. Most spaceflight is uncrewed and conducted mainly with spacecraft such as satellites in or ...
, including a mission to the planet
Mars
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terr ...
, according to the researchers.
Physiological effects
Many of the
environmental conditions experienced by humans during
spaceflight
Spaceflight (or space flight) is an application of astronautics to fly spacecraft into or through outer space, either with or without humans on board. Most spaceflight is uncrewed and conducted mainly with spacecraft such as satellites in or ...
are very different from those in which humans evolved; however, technology such as that offered by a
spaceship or
spacesuit
A space suit or spacesuit is a garment worn to keep a human alive in the harsh environment of outer space, vacuum and temperature extremes. Space suits are often worn inside spacecraft as a safety precaution in case of loss of cabin pressure, ...
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 life-support system is the combination of equipment that allows survival in an environment or situation that would not support that life in its absence. It is generally applied to systems supporting human life in situations where the outsid ...
, a group of devices that allow human beings to survive in outer space. The life support system supplies
air
The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing f ...
,
water
Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...
and
food
Food is any substance consumed by an organism for nutritional support. Food is usually of plant, animal, or fungal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals. The substance is inge ...
. 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
Proprioception ( ), also referred to as kinaesthesia (or kinesthesia), is the sense of self-movement, force, and body position. It is sometimes described as the "sixth sense".
Proprioception is mediated by proprioceptors, mechanosensory neurons ...
, changes in fluid distribution, and deterioration of the
musculoskeletal system
The human musculoskeletal system (also known as the human locomotor system, and previously the activity system) is an organ system that gives humans the ability to move using their muscular and skeletal systems. The musculoskeletal system provid ...
.
On November 2, 2017, scientists reported that significant changes in the position and structure of the
brain
A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a v ...
have been found in
astronaut
An astronaut (from the Ancient Greek (), meaning 'star', and (), meaning 'sailor') is a person trained, equipped, and deployed by a human spaceflight program to serve as a commander or crew member aboard a spacecraft. Although generally r ...
s 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
The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research.
NASA was established in 1958, succeeding t ...
-funded researchers found that lengthy journeys into
outer space
Outer space, commonly shortened to space, is the expanse that exists beyond Earth and its atmosphere and between celestial bodies. Outer space is not completely empty—it is a near-perfect vacuum containing a low density of particles, pred ...
, 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
brain
A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a v ...
s of
astronaut
An astronaut (from the Ancient Greek (), meaning 'star', and (), meaning 'sailor') is a person trained, equipped, and deployed by a human spaceflight program to serve as a commander or crew member aboard a spacecraft. Although generally r ...
s, and age them prematurely.
In March 2019, NASA reported that latent
virus
A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea.
Since Dmitri Ivanovsky's 1 ...
es in humans may be activated during
space missions
Space exploration is the use of astronomy and space technology to explore outer space. While the exploration of space is carried out mainly by astronomers with telescopes, its physical exploration though is conducted both by uncrewed rob ...
, adding possibly more risk to astronauts in future deep-space missions.
Research
Space medicine is a developing
medical practice
Medicine is the science and practice of caring for a patient, managing the diagnosis, prognosis, prevention, treatment, palliation of their injury or disease, and promoting their health. Medicine encompasses a variety of health care practic ...
that studies the
health
Health, according to the World Health Organization, is "a state of complete physical, mental and social well-being and not merely the absence of disease and infirmity".World Health Organization. (2006)''Constitution of the World Health Organiza ...
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
Palliative care (derived from the Latin root , or 'to cloak') is an interdisciplinary medical caregiving approach aimed at optimizing quality of life and mitigating suffering among people with serious, complex, and often terminal illnesses. Wit ...
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
The gravitational force equivalent, or, more commonly, g-force, is a measurement of the type of force per unit mass – typically acceleration – that causes a perception of weight, with a g-force of 1 g (not gram in mass measure ...
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
A g-suit, or anti-''g'' suit, is a flight suit worn by aviators and astronauts who are subject to high levels of acceleration force ( g). It is designed to prevent a black-out and g-LOC (g-induced loss of consciousness) caused by the blood pool ...
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
Ebullism is the formation of gas bubbles in bodily fluids due to reduced environmental pressure, for example at high altitude. It occurs because a system of liquid and gas at equilibrium will see a net conversion of liquid to gas as pressure low ...
,
hypoxia,
hypocapnia
Hypocapnia (from the Greek words υπό meaning ''below normal'' and καπνός ''kapnós'' meaning ''smoke''), also known as hypocarbia, sometimes incorrectly called acapnia, is a state of reduced carbon dioxide in the blood. Hypocapnia usually ...
, and
decompression sickness
Decompression sickness (abbreviated DCS; also called divers' disease, the bends, aerobullosis, and caisson disease) is a medical condition caused by dissolved gases emerging from solution as bubbles inside the body tissues during decompressio ...
. In addition to these, there is also
cellular mutation and
destruction
Destruction may refer to:
Concepts
* Destruktion, a term from the philosophy of Martin Heidegger
* Destructive narcissism, a pathological form of narcissism
* Self-destructive behaviour, a widely used phrase that ''conceptualises'' certain kind ...
from high energy
photons
A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they alway ...
and
sub-atomic particles
In physical sciences, a subatomic particle is a particle that composes an atom. According to the Standard Model of particle physics, a subatomic particle can be either a composite particle, which is composed of other particles (for example, a pro ...
that are present in the surroundings.
Decompression is a serious concern during the
extra-vehicular activities
Extravehicular activity (EVA) is any activity done by an astronaut in outer space outside a spacecraft. In the absence of a breathable Earthlike atmosphere, the astronaut is completely reliant on a space suit for environmental support. EVA inc ...
(EVAs) of astronauts.
[ NASA TP-2001-210196. Retrieved 2012-09-23.] 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
Emus may refer to:
* Emu
The emu () (''Dromaius novaehollandiae'') is the second-tallest living bird after its ratite relative the ostrich. It is endemic to Australia where it is the largest native bird and the only extant member of the g ...
, analogous to the difficulty of deforming an inflated balloon relative to a deflated one) and minimising
decompression risk. Investigators
[Gorguinpour, Camron et al. (2001)]
LPI "Advanced Two-System Space Suit"
University of California, Berkeley
The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California) is a public land-grant research university in Berkeley, California. Established in 1868 as the University of California, it is the state's first land-grant u ...
CB-1106. Retrieved 2012-09-23. 95 KB 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 .
In such a design, pressurization of the torso could be achieved mechanically, avoiding mobility reduction associated with pneumatic pressurization.
Vacuum
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
Gas exchange is the physical process by which gases move passively by Diffusion#Diffusion vs. bulk flow, diffusion across a surface. For example, this surface might be the air/water interface of a water body, the surface of a gas bubble in a liqui ...
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
Aerospace engineering is the primary field of engineering concerned with the development of aircraft and spacecraft. It has two major and overlapping branches: aeronautical engineering and astronautical engineering. Avionics engineering is si ...
and test subject Jim LeBlanc of
NASA
The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research.
NASA was established in 1958, succeeding t ...
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
A vacuum chamber is a rigid enclosure from which air and other gases are removed by a vacuum pump. This results in a low-pressure environment within the chamber, commonly referred to as a vacuum. A vacuum environment allows researchers to con ...
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 to 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
Ebullism is the formation of gas bubbles in bodily fluids due to reduced environmental pressure, for example at high altitude. It occurs because a system of liquid and gas at equilibrium will see a net conversion of liquid to gas as pressure low ...
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.
[ 942 pages.] Technically, ebullism is considered to begin at an elevation of around or pressures less than 6.3
kPa
KPA may refer to:
* Keele Postgraduate Association, Keele University, UK, formerly Keele Research Association (KRA)
* Kensington (Olympia) station, London, England, National Rail station code
* Kenya Ports Authority
* ''Kiln phosphoric acid'', a ...
(47
mm Hg
A millimetre of mercury is a manometric unit of pressure, formerly defined as the extra pressure generated by a column of mercury one millimetre high, and currently defined as exactly pascals. It is denoted mmHg or mm Hg.
Although not an S ...
),
known as the
Armstrong limit
The Armstrong limit or Armstrong's line is a measure of altitude above which atmospheric pressure is sufficiently low that water boils at the normal temperature of the human body. Exposure to pressure below this limit results in a rapid loss of ...
.
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
An evaporative cooler (also known as evaporative air conditioner, swamp cooler, swamp box, desert cooler and wet air cooler) is a device that cools air through the evaporation of water. Evaporative cooling differs from other air conditioning sy ...
. Severe symptoms, such as
loss of oxygen in tissue, followed by
circulatory failure
Shock is the state of insufficient blood flow to the tissues of the body as a result of problems with the circulatory system. Initial symptoms of shock may include weakness, fast heart rate, fast breathing, sweating, anxiety, and increased thir ...
and
flaccid paralysis
Flaccid paralysis is a neurological condition characterized by weakness or paralysis and reduced muscle tone without other obvious cause (e.g., trauma). This abnormal condition may be caused by disease or by trauma affecting the nerves associated ...
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
The respiratory tract is the subdivision of the respiratory system involved with the process of respiration in mammals. The respiratory tract is lined with respiratory epithelium as respiratory mucosa.
Air is breathed in through the nose to th ...
.
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
A flight suit is a full-body garment, worn while flying aircraft such as military airplanes, gliders and helicopters. These suits are generally made to keep the wearer warm, as well as being practical (plenty of pockets), and durable (includi ...
which are necessary to prevent ebullism above 19 km.
During the
Space Shuttle program
The Space Shuttle program was the fourth human spaceflight program carried out by the U.S. National Aeronautics and Space Administration (NASA), which accomplished routine transportation for Earth-to-orbit crew and cargo from 1981 to 2011. Its ...
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
Soyuz 11 (russian: link=no, Союз 11, lit=Union 11) was the only crewed mission to board the world's first space station, Salyut 1 (Soyuz 10 had soft-docked, but had not been able to enter due to latching problems). The crew, Georgy Dobrov ...
'' spacecraft;
Vladislav Volkov
Vladislav Nikolayevich Volkov (russian: Владисла́в Никола́евич Во́лков; 23 November 193529 June 1971) was a Soviet cosmonaut who flew on the Soyuz 7 and Soyuz 11 missions. The second mission terminated fatally. ,
Georgi Dobrovolski
Georgy Timofeyevich Dobrovolsky (russian: Гео́ргий Тимофе́евич Доброво́льский; 1 June 192829 June 1971) was a Soviet Union, Soviet astronaut, cosmonaut who commanded the three-man crew of the Soyuz 11 spacecraft. ...
, and
Viktor Patsayev
Viktor Ivanovich Patsayev (russian: Ви́ктор Ива́нович Паца́ев; 19 June 193329 June 1971) was a Soviet cosmonaut who flew on the Soyuz 11 mission and was part of the third space crew to die during a space flight. On boar ...
. 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 , 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
In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes:
* ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visi ...
of direct, unfiltered
sunlight
Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light. On Earth, sunlight is scattered and filtered through Earth's atmosphere, and is obvious as daylight when t ...
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
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...
rays, however, may cause severe sunburn.
Radiation
![PIA17601-Comparisons-RadiationExposure-MarsTrip-20131209](https://upload.wikimedia.org/wikipedia/commons/e/ef/PIA17601-Comparisons-RadiationExposure-MarsTrip-20131209.png)
Without the protection of Earth's
atmosphere
An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...
and
magnetosphere
In astronomy and planetary science, a magnetosphere is a region of space surrounding an astronomical object in which charged particles are affected by that object's magnetic field. It is created by a celestial body with an active interior dynam ...
astronauts are exposed to high levels of
radiation
In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes:
* ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visi ...
. High levels of radiation damage
lymphocytes
A lymphocyte is a type of white blood cell (leukocyte) in the immune system of most vertebrates. Lymphocytes include natural killer cells (which function in cell-mediated, cytotoxic innate immunity), T cells (for cell-mediated, cytotoxic adap ...
, cells heavily involved in maintaining the
immune system
The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splinte ...
; this damage contributes to the lowered
immunity
Immunity may refer to:
Medicine
* Immunity (medical), resistance of an organism to infection or disease
* ''Immunity'' (journal), a scientific journal published by Cell Press
Biology
* Immune system
Engineering
* Radiofrequence immunity desc ...
experienced by astronauts. Radiation has also recently been linked to a higher incidence of
cataracts
A cataract is a cloudy area in the lens of the eye that leads to a decrease in vision. Cataracts often develop slowly and can affect one or both eyes. Symptoms may include faded colors, blurry or double vision, halos around light, trouble w ...
in astronauts. Outside the protection of low Earth orbit,
galactic cosmic ray
Cosmic rays are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar System in our own ...
s present further challenges to human spaceflight, as the
health threat from cosmic rays
Health threats from cosmic rays are the dangers posed by cosmic rays to astronauts on interplanetary missions or any missions that venture through the Van-Allen Belts or outside the Earth's magnetosphere. They are one of the greatest barriers ...
significantly increases the chances of cancer over a decade or more of exposure. A
NASA
The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research.
NASA was established in 1958, succeeding t ...
-supported study reported that radiation may harm the
brain
A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a v ...
of
astronauts
An astronaut (from the Ancient Greek (), meaning 'star', and (), meaning 'sailor') is a person trained, equipped, and deployed by a human spaceflight program to serve as a commander or crew member aboard a spacecraft. Although generally r ...
and accelerate the onset of
Alzheimer's disease
Alzheimer's disease (AD) is a neurodegeneration, neurodegenerative disease that usually starts slowly and progressively worsens. It is the cause of 60–70% of cases of dementia. The most common early symptom is difficulty in short-term me ...
.
Solar flare
A solar flare is an intense localized eruption of electromagnetic radiation in the Sun's atmosphere. Flares occur in active regions and are often, but not always, accompanied by coronal mass ejections, solar particle events, and other solar phe ...
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
The International Space Station (ISS) is the largest modular space station currently in low Earth orbit. It is a multinational collaborative project involving five participating space agencies: NASA (United States), Roscosmos (Russia), JAXA ...
(ISS) are partially protected from the space environment by Earth's magnetic field, as the
magnetosphere
In astronomy and planetary science, a magnetosphere is a region of space surrounding an astronomical object in which charged particles are affected by that object's magnetic field. It is created by a celestial body with an active interior dynam ...
deflects
solar wind
The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the sola ...
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 crew of
Expedition 10
Expedition 10 (2004–2005) was the tenth expedition to the International Space Station, using the Soyuz TMA-5, which stayed during the expedition for emergency evacuation.
Crew
Mission parameters
*Perigee: 384 km
*Apogee: 396 k ...
took shelter as a precaution in 2005 in a more heavily shielded part of the station designed for this purpose. However, beyond the limited protection of Earth's
magnetosphere
In astronomy and planetary science, a magnetosphere is a region of space surrounding an astronomical object in which charged particles are affected by that object's magnetic field. It is created by a celestial body with an active interior dynam ...
, interplanetary human missions are much more vulnerable. Lawrence Townsend of the University of Tennessee and others have studied
the most powerful solar flare ever recorded. Radiation doses astronauts would receive from a flare of this magnitude could cause acute radiation sickness and possibly even death.
There is scientific concern that extended spaceflight might slow down the body's ability to protect itself against diseases. Radiation can penetrate living tissue and cause both short and long-term damage to the bone marrow stem cells which create the blood and immune systems. In particular, it causes '
chromosomal
A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...
aberrations' in
lymphocyte
A lymphocyte is a type of white blood cell (leukocyte) in the immune system of most vertebrates. Lymphocytes include natural killer cells (which function in cell-mediated, cytotoxic innate immunity), T cells (for cell-mediated, cytotoxic ad ...
s. As these cells are central to the
immune system
The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splinte ...
, any damage weakens the immune system, which means that in addition to increased vulnerability to new exposures,
virus
A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea.
Since Dmitri Ivanovsky's 1 ...
es already present in the body—which would normally be suppressed—become active. In space,
T-cells
A T cell is a type of lymphocyte. T cells are one of the important white blood cells of the immune system and play a central role in the adaptive immune response. T cells can be distinguished from other lymphocytes by the presence of a T-cell rec ...
(a form of lymphocyte) are less able to reproduce properly, and the T-cells that do reproduce are less able to fight off infection. Over time immunodeficiency results in the rapid spread of infection among crew members, especially in the confined areas of space flight systems.
On 31 May 2013, NASA scientists reported that a possible
human mission to Mars
The idea of sending humans to Mars has been the subject of aerospace engineering and scientific studies since the late 1940s as part of the broader exploration of Mars. Some have also considered exploring the Martian moons of Phobos and Deimos. ...
may involve a great
radiation risk based on the amount of
energetic particle radiation detected by the
RAD
RAD or Rad may refer to:
People
* Robert Anthony Rad Dougall (born 1951), South African former racing driver
* Rad Hourani, Canadian fashion designer and artist
* Nickname of Leonardus Rad Kortenhorst (1886–1963), Dutch politician
* Radley R ...
on the
Mars Science Laboratory
Mars Science Laboratory (MSL) is a robotic spacecraft, robotic space probe mission to Mars launched by NASA on November 26, 2011, which successfully landed ''Curiosity (rover), Curiosity'', a Mars rover, in Gale (crater), Gale Crater on August ...
while traveling from the
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
to
Mars
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terr ...
in 2011–2012.
In September 2017, NASA reported
radiation levels
Ionizing radiation (or ionising radiation), including nuclear radiation, consists of subatomic particles or electromagnetic waves that have sufficient energy to ionize atoms or molecules by detaching electrons from them. Some particles can travel ...
on the surface of the planet
Mars
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terr ...
were temporarily
doubled, and were associated with an
aurora
An aurora (plural: auroras or aurorae), also commonly known as the polar lights, is a natural light display in Earth's sky, predominantly seen in high-latitude regions (around the Arctic and Antarctic). Auroras display dynamic patterns of bri ...
25-times brighter than any observed earlier, due to a massive, and unexpected,
solar storm
A solar storm is a disturbance on the Sun, which can emanate outward across the heliosphere, affecting the entire Solar System, including Earth and its magnetosphere, and is the cause of space weather in the short-term with long-term patterns comp ...
in the middle of the month.
Weightlessness
Following the advent of
space station
A space station is a spacecraft capable of supporting a human crew in orbit for an extended period of time, and is therefore a type of space habitat. It lacks major propulsion or landing systems. An orbital station or an orbital space station i ...
s that can be inhabited for long periods of time, exposure to
weightlessness
Weightlessness is the complete or near-complete absence of the sensation of weight. It is also termed zero gravity, zero G-force, or zero-G.
Weight is a measurement of the force on an object at rest in a relatively strong gravitational fi ...
has been demonstrated to have some deleterious effects on human health. Humans are well-adapted to the physical conditions at the surface of the earth, and so in response to weightlessness, various
physiological systems begin to change, and in some cases,
atrophy
Atrophy is the partial or complete wasting away of a part of the body. Causes of atrophy include mutations (which can destroy the gene to build up the organ), poor nourishment, poor circulation, loss of hormonal support, loss of nerve supply t ...
. Though these changes are usually temporary, some do have a long-term impact on human
health
Health, according to the World Health Organization, is "a state of complete physical, mental and social well-being and not merely the absence of disease and infirmity".World Health Organization. (2006)''Constitution of the World Health Organiza ...
.
Short-term exposure to microgravity causes
space adaptation syndrome, self-limiting nausea caused by derangement of the
vestibular system
The vestibular system, in vertebrates, is a sensory system that creates the sense of balance and spatial orientation for the purpose of coordinating movement with balance. Together with the cochlea, a part of the auditory system, it constitutes ...
. Long-term exposure causes multiple health problems, one of the most significant being loss of bone and muscle mass. Over time these
deconditioning Deconditioning is adaptation of an organism to less demanding environment, or, alternatively, the decrease of physiological adaptation to normal conditions. Decondition may result from decreased physical activity, prescribed bed rest, orthopedic cas ...
effects can impair astronauts' performance, increase their risk of injury, reduce their
aerobic capacity
VO2 max (also maximal oxygen consumption, maximal oxygen uptake or maximal aerobic capacity) is the maximum rate of oxygen consumption attainable during physical exertion. The name is derived from three abbreviations: "V̇" for volume (the dot ap ...
, and slow down their
cardiovascular system
The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, tha ...
. As the human body consists mostly of fluids, gravity tends to force them into the lower half of the body, and our bodies have many systems to balance this situation. When released from the pull of gravity, these systems continue to work, causing a general redistribution of fluids into the upper half of the body. This is the cause of the round-faced 'puffiness' seen in astronauts.
Redistributing fluids around the body itself causes balance disorders,
distorted vision
Distorted may refer to:
* Anything subject to distortion
* Distorted (band), a progressive deathdoom metal band from Bat-Yam, Israel
* ''Distorted'' (EP), an extended play by the band Distorted
* ''Distorted'' (film) (2018)
* Distorted Music Fest ...
, and a loss of taste and smell.
A 2006 Space Shuttle experiment found that ''
Salmonella typhimurium
''Salmonella enterica'' subsp. ''enterica'' is a subspecies of ''Salmonella enterica'', the rod-shaped, flagellated, aerobic, Gram-negative bacterium. Many of the pathogenic serovars of the ''S. enterica'' species are in this subspecies, includi ...
'', a bacterium that can cause
food poisoning
Foodborne illness (also foodborne disease and food poisoning) is any illness resulting from the spoilage of contaminated food by pathogenic bacteria, viruses, or parasites that contaminate food,
as well as prions (the agents of mad cow disease) ...
, became more virulent when cultivated in space.
On April 29, 2013, scientists in
Rensselaer Polytechnic Institute
Rensselaer Polytechnic Institute () (RPI) is a private research university in Troy, New York, with an additional campus in Hartford, Connecticut. A third campus in Groton, Connecticut closed in 2018. RPI was established in 1824 by Stephen Van ...
, funded by
NASA
The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research.
NASA was established in 1958, succeeding t ...
, reported that, during
spaceflight
Spaceflight (or space flight) is an application of astronautics to fly spacecraft into or through outer space, either with or without humans on board. Most spaceflight is uncrewed and conducted mainly with spacecraft such as satellites in or ...
on the
International Space Station
The International Space Station (ISS) is the largest modular space station currently in low Earth orbit. It is a multinational collaborative project involving five participating space agencies: NASA (United States), Roscosmos (Russia), JAXA ...
,
microbes
A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...
seem to adapt to the
space environment
Space environment is a branch of astronautics, aerospace engineering and space physics that seeks to understand and address conditions existing in space that affect the design and operation of spacecraft. A related subject, space weather, deals ...
in ways "not observed on Earth" and in ways that "can lead to increases in growth and
virulence
Virulence is a pathogen's or microorganism's ability to cause damage to a host.
In most, especially in animal systems, virulence refers to the degree of damage caused by a microbe to its host. The pathogenicity of an organism—its ability to ca ...
".
More recently, in 2017,
bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
were found to be more resistant to
antibiotic
An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention of ...
s and to thrive in the near-weightlessness of space.
Microorganism
A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...
s have been observed to survive the
vacuum
A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often dis ...
of outer space.
Motion sickness
![Bruce McCandless II during EVA in 1984](https://upload.wikimedia.org/wikipedia/commons/9/91/Bruce_McCandless_II_during_EVA_in_1984.jpg)
The most common problem experienced by humans in the initial hours of weightlessness is known as
space adaptation syndrome or SAS, commonly referred to as space sickness. It is related to
motion sickness
Motion sickness occurs due to a difference between actual and expected motion. Symptoms commonly include nausea, vomiting, cold sweat, headache, dizziness, tiredness, loss of appetite, and increased salivation. Complications may rarely include d ...
, and arises as the
vestibular system
The vestibular system, in vertebrates, is a sensory system that creates the sense of balance and spatial orientation for the purpose of coordinating movement with balance. Together with the cochlea, a part of the auditory system, it constitutes ...
adapts to weightlessness.
Symptoms of SAS include
nausea
Nausea is a diffuse sensation of unease and discomfort, sometimes perceived as an urge to vomit. While not painful, it can be a debilitating symptom if prolonged and has been described as placing discomfort on the chest, abdomen, or back of the ...
and
vomiting
Vomiting (also known as emesis and throwing up) is the involuntary, forceful expulsion of the contents of one's stomach through the mouth and sometimes the Human nose, nose.
Vomiting can be the result of ailments like Food-poisoning, foo ...
,
vertigo
Vertigo is a condition where a person has the sensation of movement or of surrounding objects moving when they are not. Often it feels like a spinning or swaying movement. This may be associated with nausea, vomiting, sweating, or difficulties w ...
,
headache
Headache is the symptom of pain in the face, head, or neck. It can occur as a migraine, tension-type headache, or cluster headache. There is an increased risk of depression in those with severe headaches.
Headaches can occur as a result ...
s,
lethargy
Lethargy is a state of tiredness, sleepiness, weariness, fatigue, sluggishness or lack of energy. It can be accompanied by depression, decreased motivation, or apathy. Lethargy can be a normal response to inadequate sleep, overexertion, overwo ...
, and overall malaise.
[ The first case of SAS was reported by ]cosmonaut
An astronaut (from the Ancient Greek (), meaning 'star', and (), meaning 'sailor') is a person trained, equipped, and deployed by a human spaceflight program to serve as a commander or crew member aboard a spacecraft. Although generally r ...
Gherman Titov
Gherman Stepanovich Titov (russian: Герман Степанович Титов; 11 September 1935 – 20 September 2000) was a Soviet cosmonaut who, on 6 August 1961, became the second human to orbit the Earth, aboard Vostok 2, preceded by Y ...
in 1961. Since then, roughly 45% of all people who have flown in space have suffered from this condition.
Bone and muscle deterioration
A major effect of long-term weightlessness involves the loss of bone
A bone is a Stiffness, rigid Organ (biology), organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red blood cell, red and white blood cells, store minerals, provid ...
and muscle
Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...
mass. Without the effects of gravity, skeletal muscle
Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...
is no longer required to maintain posture and the muscle groups used in moving around in a weightless environment differ from those required in terrestrial locomotion. In a weightless environment, astronauts put almost no weight on the back muscle
Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...
s or leg muscles used for standing up. Those muscles then start to weaken and eventually get smaller. Consequently, some muscles atrophy rapidly, and without regular exercise astronauts can lose up to 20% of their muscle mass in just 5 to 11 days. The types of muscle fibre
A muscle cell is also known as a myocyte when referring to either a cardiac muscle cell (cardiomyocyte), or a smooth muscle cell as these are both small cells. A skeletal muscle cell is long and threadlike with many nuclei and is called a muscl ...
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. Advances in research on exercise, hormone supplements, and medication may help maintain muscle and body mass.
Bone
A bone is a Stiffness, rigid Organ (biology), organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red blood cell, red and white blood cells, store minerals, provid ...
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. Due to microgravity and the decreased load on the bones, there is a rapid increase in bone loss, from 3% cortical bone loss per decade to about 1% every month the body is exposed to microgravity, for an otherwise healthy adult. The rapid change in bone density is dramatic, making bones frail and resulting in symptoms that resemble those of osteoporosis. On Earth, the bones are constantly being shed and regenerated through a well-balanced system which involves signaling of osteoblasts and osteoclasts. These systems are coupled, so that whenever bone is broken down, newly formed layers take its place—neither should happen without the other, in a healthy adult. In space, however, there is an increase in osteoclast activity due to microgravity. This is a problem because osteoclasts break down the bones into minerals that are reabsorbed by the body. Osteoblasts are not consecutively active with the osteoclasts, causing the bone to be constantly diminished with no recovery. This increase in osteoclasts activity has been seen particularly in the pelvic region because this is the region that carries the biggest load with gravity present. A study demonstrated that in healthy mice, osteoclasts appearance increased by 197%, accompanied by a down-regulation of osteoblasts and growth factors that are known to help with the formation of new bone, after only sixteen days of exposure to microgravity. Elevated blood calcium
Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to ...
levels from the lost bone result in dangerous calcification of soft tissues and potential kidney stone
Kidney stone disease, also known as nephrolithiasis or urolithiasis, is a crystallopathy where a solid piece of material (kidney stone) develops in the urinary tract. Kidney stones typically form in the kidney and leave the body in the urine s ...
formation. It is still unknown whether bone recovers completely. Unlike people with osteoporosis, astronauts eventually regain their bone density. After a 3–4 month trip into space, it takes about 2–3 years to regain lost bone density. New techniques are being developed to help astronauts recover faster. Research on diet, exercise, and medication may hold the potential to aid the process of growing new bone.
To prevent some of these adverse physiological
Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical ...
effects, the ISS is equipped with two treadmills (including the COLBERT), and the aRED (advanced Resistive Exercise Device), which enable various weight-lifting exercises which add muscle but do nothing for bone density, and a stationary bicycle; each astronaut spends at least two hours per day exercising on the equipment. Astronauts use bungee cords to strap themselves to the treadmill. Astronauts subject to long periods of weightlessness wear pants with elastic bands attached between waistband and cuffs to compress the leg bones and reduce osteopenia.
Currently, NASA
The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research.
NASA was established in 1958, succeeding t ...
is using advanced computational tools to understand how to best counteract the bone and muscle atrophy experienced by astronauts in microgravity environments for prolonged periods of time. The Human Research Program's Human Health Countermeasures Element chartered the Digital Astronaut Project to investigate targeted questions about exercise countermeasure regimes. NASA is focusing on integrating a model of the advanced Resistive Exercise Device (ARED) currently on board the International Space Station
The International Space Station (ISS) is the largest modular space station currently in low Earth orbit. It is a multinational collaborative project involving five participating space agencies: NASA (United States), Roscosmos (Russia), JAXA ...
with OpenSim musculoskeletal models of humans exercising with the device. The goal of this work is to use inverse dynamics to estimate joint torques and muscle forces resulting from using the ARED, and thus more accurately prescribe exercise regimens for the astronauts. These joint torques and muscle forces could be used in conjunction with more fundamental computational simulations of bone remodeling and muscle adaptation in order to more completely model the end effects of such countermeasures, and determine whether a proposed exercise regime would be sufficient to sustain astronaut musculoskeletal health.
Fluid redistribution
In space, astronauts lose fluid volume—including up to 22% of their blood volume. Because it has less blood to pump, the heart will atrophy
Atrophy is the partial or complete wasting away of a part of the body. Causes of atrophy include mutations (which can destroy the gene to build up the organ), poor nourishment, poor circulation, loss of hormonal support, loss of nerve supply t ...
. A weakened heart results in low blood pressure and can produce a problem with "orthostatic tolerance", or the body's ability to send enough oxygen to the brain without the astronaut's fainting or becoming dizzy. "Under the effects of the earth's gravity
In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...
, blood and other body fluids are pulled towards the lower body. When gravity is taken away or reduced during space exploration, the blood tends to collect in the upper body instead, resulting in facial edema
Edema, also spelled oedema, and also known as fluid retention, dropsy, hydropsy and swelling, is the build-up of fluid in the body's Tissue (biology), tissue. Most commonly, the legs or arms are affected. Symptoms may include skin which feels t ...
and other unwelcome side effects. Upon return to earth, the blood begins to pool in the lower extremities again, resulting in orthostatic hypotension
Orthostatic hypotension, also known as postural hypotension, is a medical condition wherein a person's blood pressure drops when standing up or sitting down. Primary orthostatic hypertension is also often referred to as neurogenic orthostatic hyp ...
."
Disruption of senses
=Vision
=
In 2013 NASA published a study that found changes to the eyes and eyesight of monkeys with spaceflights longer than 6 months. Noted changes included a flattening of the eyeball and changes to the retina. Space traveler's eye-sight can become blurry after too much time in space. Another effect is known as cosmic ray visual phenomena.
Since dust can not settle in zero gravity, small pieces of dead skin or metal can get in the eye, causing irritation and increasing the risk of infection.
Long spaceflights can also alter a space traveler's eye movements (particularly the vestibulo-ocular reflex).
Intracranial pressure
Because weightlessness increases the amount of fluid in the upper part of the body, astronauts experience increased intracranial pressure
Intracranial pressure (ICP) is the pressure exerted by fluids such as cerebrospinal fluid (CSF) inside the skull and on the brain tissue. ICP is measured in millimeters of mercury (mmHg) and at rest, is normally 7–15 Millimeter of mercury, mmHg ...
. This appears to increase pressure on the backs of the eyeballs, affecting their shape and slightly crushing the optic nerve
In neuroanatomy, the optic nerve, also known as the second cranial nerve, cranial nerve II, or simply CN II, is a paired cranial nerve that transmits visual system, visual information from the retina to the brain. In humans, the optic nerve i ...
. This effect was noticed in 2012 in a study using MRI
Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio waves ...
scans of astronauts who had returned to Earth following at least one month in space. Such eyesight problems could be a major concern for future deep space flight missions, including a crewed mission
Human spaceflight (also referred to as manned spaceflight or crewed spaceflight) is spaceflight with a crew or passengers aboard a spacecraft, often with the spacecraft being operated directly by the onboard human crew. Spacecraft can also be ...
to the planet Mars
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terr ...
.
If indeed elevated intracranial pressure is the cause, artificial gravity might present one solution, as it would for many human health risks in space. However, such artificial gravitational systems have yet to be proven. More, even with sophisticated artificial gravity, a state of relative microgravity may remain, the risks of which remain unknown.
=Taste
=
One effect of weightlessness on humans is that some astronauts report a change in their sense of taste
The gustatory system or sense of taste is the sensory system that is partially responsible for the perception of taste (flavor). Taste is the perception produced or stimulated when a substance in the mouth reacts chemically with taste receptor ...
when in space. Some astronauts find that their food is bland, others find that their favorite foods no longer taste as good (one who enjoyed coffee disliked the taste so much on a mission that he stopped drinking it after returning to Earth); some astronauts enjoy eating certain foods that they would not normally eat, and some experience no change whatsoever. Multiple tests have not identified the cause, and several theories have been suggested, including food degradation, and psychological changes such as boredom. Astronauts often choose strong-tasting food to combat the loss of taste.
Additional physiological effects
Within one month the human skeleton fully extends in weightlessness, causing height to increase by an inch. After two months, calluses on the bottoms of feet molt
In biology, moulting (British English), or molting (American English), also known as sloughing, shedding, or in many invertebrates, ecdysis, is the manner in which an animal routinely casts off a part of its body (often, but not always, an outer ...
and fall off from lack of use, leaving soft new skin. Tops of feet become, by contrast, raw and painfully sensitive, as they rub against the handrails feet are hooked into for stability. Tears cannot be shed while crying, as they stick together into a ball. In microgravity odors quickly permeate the environment, and NASA found in a test that the smell of cream sherry
Sherry ( es, jerez ) is a fortified wine made from white grapes that are grown near the city of Jerez de la Frontera in Andalusia, Spain. Sherry is produced in a variety of styles made primarily from the Palomino grape, ranging from light ver ...
triggered the gag reflex. Various other physical discomforts such as back and abdominal pain are common because of the readjustment to gravity, where in space there was no gravity and these muscles could freely stretch. These may be part of the asthenization syndrome reported by cosmonauts
An astronaut (from the Ancient Greek (), meaning 'star', and (), meaning 'sailor') is a person trained, equipped, and deployed by a human spaceflight program to serve as a commander or crew member aboard a spacecraft. Although generally r ...
living in space over an extended period of time, but regarded as anecdotal by astronauts. Fatigue, listlessness, and psychosomatic worries are also part of the syndrome. The data is inconclusive; however, the syndrome does appear to exist as a manifestation of the internal and external stress crews in space must face.
Psychological effects
Research
The psychological effects of living in space have not been clearly analyzed but analogies on Earth do exist, such as Arctic
The Arctic ( or ) is a polar regions of Earth, polar region located at the northernmost part of Earth. The Arctic consists of the Arctic Ocean, adjacent seas, and parts of Canada (Yukon, Northwest Territories, Nunavut), Danish Realm (Greenla ...
research stations and submarine
A submarine (or sub) is a watercraft capable of independent operation underwater. It differs from a submersible, which has more limited underwater capability. The term is also sometimes used historically or colloquially to refer to remotely op ...
s. The enormous stress on the crew, coupled with the body adapting to other environmental changes, can result in anxiety, insomnia and depression.
Stress
There has been considerable evidence that psychosocial stressors are among the most important impediments to optimal crew morale and performance. Cosmonaut Valery Ryumin
Valery Victorovich Ryumin (russian: Валерий Викторович Рюмин; 16 August 1939 – 6 June 2022) was a Soviet cosmonaut.
Biography
In 1958, he graduated from the Kaliningrad Mechanical Engineering Technical College with the ...
, twice Hero of the Soviet Union, quotes this passage from "The Handbook of Hymen" by O. Henry in his autobiographical book about the Salyut 6 mission: "If you want to instigate the art of manslaughter just shut two men up in an eighteen by twenty-foot cabin for a month. Human nature won't stand it."
NASA's interest in psychological stress caused by space travel, initially studied when their crewed missions began, was rekindled when astronauts joined cosmonauts on the Russian space station Mir. Common sources of stress in early American missions included maintaining high performance while under public scrutiny, as well as isolation from peers and family. On the ISS, the latter is still often a cause of stress, such as when NASA Astronaut Daniel Tani
Daniel M. Tani (born February 1, 1961) is an American engineer and retired NASA astronaut. He was born in Ridley Park, Pennsylvania, but considers Lombard, Illinois, to be his hometown.
With Peggy Whitson, Tani conducted the 100th spacewalk on ...
's mother died in a car accident, and when Michael Fincke
Edward Michael "Mike"/"Spanky" Fincke
(born March 14, 1967) is an American astronaut who formerly held the American record for the most time in space (381.6 days). His record was broken by Scott Kelly on October 16, 2015.
Mike Fincke was bor ...
was forced to miss the birth of his second child.
Sleep
The amount and quality of sleep
Sleep is a sedentary state of mind and body. It is characterized by altered consciousness, relatively inhibited sensory activity, reduced muscle activity and reduced interactions with surroundings. It is distinguished from wakefulness by a de ...
experienced in space is poor due to highly variable light and dark cycles on flight decks and poor illumination during daytime hours in the spacecraft. 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
A circadian rhythm (), or circadian cycle, is a natural, internal process that regulates the sleep–wake cycle and repeats roughly every 24 hours. It can refer to any process that originates within an organism (i.e., Endogeny (biology), endogeno ...
have profound effects on the neurobehavioural responses of the crew and aggravate the psychological stresses they already experience. Sleep is disturbed on the ISS
The International Space Station (ISS) is the largest modular space station currently in low Earth orbit. It is a multinational collaborative project involving five participating space agencies: NASA (United States), Roscosmos (Russia), JAXA (J ...
regularly due to mission demands, such as the scheduling of incoming or departing space vehicles. Sound levels in the station are unavoidably high because the atmosphere is unable to thermosiphon
Thermosiphon (or thermosyphon) is a method of passive heat exchange, based on natural convection, which circulates a fluid without the necessity of a mechanical pump. Thermosiphoning is used for circulation of liquids and volatile gases in heat ...
; fans are required at all times to allow processing of the atmosphere, which would stagnate in the freefall (zero-g) environment. Fifty percent of Space Shuttle
The Space Shuttle is a retired, partially reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. Its official program na ...
astronauts took sleeping pills and still got 2 hours less sleep each night in space than they did on the ground. NASA is researching two areas which may provide the keys to a better night's sleep, as improved sleep decreases fatigue and increases daytime productivity. A variety of methods for combating this phenomenon are constantly under discussion.
Duration of space travel
A study of the longest spaceflight concluded that the first three weeks represent a critical period where attention is adversely affected because of the demand to adjust to the extreme change of environment. While Skylab's three crews remained in space 1, 2, and 3 months respectively, long-term crews on Salyut 6, Salyut 7, and the ISS remain about 5–6 months, while MIR expeditions often lasted longer. The ISS working environment includes further stress caused by living and working in cramped conditions with people from very different cultures who speak different languages. First-generation space stations had crews who spoke a single language, while 2nd and 3rd generation stations have crews from many cultures who speak many languages. The ISS is unique because visitors are not classed automatically into 'host' or 'guest' categories as with previous stations and spacecraft, and may not suffer from feelings of isolation in the same way.
Future use
The sum of human experience has resulted in the accumulation of 58 solar years in space and a much better understanding of how the human body adapts. In the future, industrialisation of space and exploration of inner and outer planets will require humans to endure longer and longer periods in space. The majority of current 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
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terr ...
with current technology is estimated to involve at least 18 months in transit alone. Knowing 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 adequate for coping 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 for coping not only with trauma but also with the adaptive responses of the human body in space.
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 very young are completely unknown. On October 29, 1998, John Glenn, one of the original Mercury 7, returned to space at the age of 77. His space flight, which lasted 9 days, provided NASA with important information about the effects of space flight on older people. Factors such as nutritional requirements and physical environments which have so far not been examined will become important. Overall, there is little data on the manifold effects of living in space, and this makes attempts toward mitigating the risks during a lengthy space habitation difficult. Testbed
A testbed (also spelled test bed) is a platform for conducting rigorous, transparent, and replicable testing of scientific theories, computational tools, and new technologies.
The term is used across many disciplines to describe experimental rese ...
s such as the ISS are currently being utilized to research some of these risks.
The environment of space is still largely unknown, and there will likely be as-yet-unknown hazards. Meanwhile, future technologies such as artificial gravity
Artificial gravity is the creation of an inertial force that mimics the effects of a gravitational force, usually by rotation.
Artificial gravity, or rotational gravity, is thus the appearance of a centrifugal force in a rotating frame of re ...
and more complex bioregenerative life support system
A life-support system is the combination of equipment that allows survival in an environment or situation that would not support that life in its absence. It is generally applied to systems supporting human life in situations where the outsid ...
s may someday be capable of mitigating some risks.
See also
* Fatigue and sleep loss during spaceflight
Sleeping in space is an important part of space medicine and mission planning, with impacts on the health, capabilities and morale of astronauts.
Human spaceflight often requires astronaut crews to endure long periods without rest. Studies hav ...
* Food systems on space exploration missions
* Ionizing radiation#Spaceflight
* Intervertebral disc damage and spaceflight Astronauts have expressed an increased incidence of back pain during spaceflight and herniated intervertebral discs (IVD) have been diagnosed upon return of Skylab and Shuttle spaceflight participants.
These conditions and symptoms may be from pr ...
* Locomotion in space
Locomotion in space includes all actions or methods used to move one's body in microgravity conditions through the outer space environment. Locomotion in these conditions is different from locomotion in a gravitational field. There are many facto ...
* Mars Analog Habitats
* Medical treatment during spaceflight
* Overview effect
The overview effect is a cognitive shift reported by some astronauts while viewing the Earth from space. Researchers have characterized the effect as "a state of awe with self-transcendent qualities, precipitated by a particularly striking vis ...
* Reduced muscle mass, strength and performance in space
Even before the very beginning of human space exploration, serious and reasonable concerns were expressed about exposure of humans to the microgravity of space due to the potential systemic effects on terrestrially-evolved life forms adapted to G ...
* Renal stone formation in space
* Environmental control system
In aeronautics, an environmental control system (ECS) of an aircraft is an essential component which provides air supply, Air conditioning, thermal control and cabin pressurization for the Aircrew, crew and passengers. Additional functions incl ...
* Space colonization
Space colonization (also called space settlement or extraterrestrial colonization) is the use of outer space or celestial bodies other than Earth for permanent habitation or as extraterrestrial territory.
The inhabitation and territori ...
* Spaceflight radiation carcinogenesis
* Team composition and cohesion in spaceflight missions Selection, training, cohesion and psychosocial adaptation influence performance and, as such, are relevant factors to consider while preparing for costly, long-duration spaceflight missions in which the performance objectives will be demanding, endu ...
* Visual impairment due to intracranial pressure
Spaceflight-associated neuro-ocular syndrome (SANS), previously known as ''Spaceflight-induced visual impairment'', is hypothesized to be a result of increased intracranial pressure. The study of visual changes and intracranial pressure (ICP) in ...
References
Further reading
* NASA Report: Space Travel 'Inherently Hazardous' to Human Health. Leonard David. 2001
* ''Space Physiology and Medicine''. Third edition. A. E. Nicogossian, C. L. Huntoon and S. L. Pool. Lea & Febiger, 1993.
* L.-F. Zhang. Vascular adaptation to microgravity: What have we learned?. ''Journal of Applied Physiology
The ''Journal of Applied Physiology'' is a monthly peer-reviewed medical journal of physiology published by the American Physiological Society. The journal was established in 1948, and is currently edited by Sue Bodine. According to the ''Journal ...
''. 91(6) (pp 2415–2430), 2001.
* G. Carmeliet, Vico. L, Bouillon R. '' Critical Reviews in Eukaryotic Gene Expression''. Vol 11(1–3) (pp 131–144), 2001.
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* Styf, Jorma R.; Hutchinson, Karen; Carlsson, Sven G. & Hargens, Alan R. (November–December 2001). "Depression, Mood State, and Back Pain During Microgravity Simulated by Bed Rest". ''Psychosomatic Medicine
Psychosomatic medicine is an interdisciplinary medical field exploring the relationships among social, psychological, behavioral factors on bodily processes and quality of life in humans and animals.
The academic forebear of the modern field of ...
''. 63 (6): 862–4.
* Altitude Decompression Sickness Susceptibility, MacPherson, G; ''Aviation, Space, and Environmental Medicine
''Aerospace Medicine and Human Performance'' (''AMHP'') is a peer-reviewed scientific journal in the field of aviation and aerospace medicine. It was founded as the ''Journal of Aviation Medicine'' in 1930 by Louis H. Bauer, M.D., and is publishe ...
'', Volume 78, Number 6, June 2007, pp. 630–631(2)
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