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Astronaut
Marsha Ivins demonstrates the effects of zero-G on her hair in space
Humans
venturing into the environment of space can have negative effects on the body.
[1] Significant adverse effects of long-term
weightlessness include
muscle atrophy and deterioration of the
skeleton (
spaceflight osteopenia).
[2] Other significant effects include a slowing of
cardiovascular system functions, decreased production of
red blood cells,
balance disorders,
eyesight disorders and a weakening of the
immune system. Additional symptoms include
fluid redistribution (causing the "moon-face" appearance typical in pictures of astronauts experiencing weightlessness),
[3][4] loss of
body mass,
nasal congestion,
sleep disturbance, and excess
flatulence.
The engineering problems associated with leaving
Earth and developing
space propulsion
systems have been examined for over a century, and millions of
man-hours of research have been spent on them. In recent years there has
been an increase in research 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.
[5][6]
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.
[7] 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.
Of course, it is not possible to remove all hazards; the most
important factor affecting human physical well-being in space is
weightlessness, more accurately defined as
Micro-g 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 2 November 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.
[8][9]
Research
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
preventative and
palliative measures to ease the suffering caused by living in an environment to which humans are not well adapted.
Ascent and reentry
During takeoff and reentry space travelers can experience several
times normal gravity. An untrained person can usually withstand about
3g, but can blackout 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 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.
[10] Decompression is a serious concern during the
extra-vehicular activities (EVAs) of astronauts.
[11] Current EMU designs take this and other issues into consideration, and have evolved over time.
[12][13] 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
[14]
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).
[13][15]
In such a design, pressurization of the torso could be achieved
mechanically, avoiding mobility reduction associated with pneumatic
pressurization.
[14]
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
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.
[16] Exposure to vacuum for up to 30 seconds is unlikely to cause permanent physical damage.
[17]
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.
[18][19]
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.
[20]
In December 1966,
aerospace engineer and test subject Jim LeBlanc of
NASA was partaking 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.
[21] At some point during the test, LeBlanc's pressurization hose became detached from the space suit.
[22]
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.
[23]
The chamber was rapidly pressurized and LeBlanc was given emergency
oxygen 25 seconds later. He recovered almost immediately with just an
earache and no permanent damage.
[24][25]
Another effect from a vacuum is a condition is 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.
[26] 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),
[27] known as the
Armstrong limit.
[10]
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.
[10] The
lungs also collapse in this process, but will continue to release water vapour leading to cooling and ice formation in the
respiratory tract.
[10] A rough estimate is that a human will have about 90 seconds to be recompressed, after which death may be unavoidable.
[26][28] Swelling from ebullism can be reduced by containment in a
flight suit which are necessary to prevent ebullism above 19 km.
[20] 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 Torr).
[29]
The only known humans to have died of space exposure are the three crew members of the
Soyuz 11 spacecraft:
Vladislav Volkov,
Georgi Dobrovolski and
Viktor Patsayev. During re-entry on June 30, 1971, the ship's depressurization resulted in the death of the entire crew.
[30][31]
Two other people were decompressed accidentally during space mission
training programs on the ground, but both incidents were less than 5
minutes in duration, and both victims survived.
[10]
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.
[32]
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
Comparison of Radiation Doses – includes the amount detected on the trip from Earth to Mars by the
RAD on the
MSL (2011–2013).
[33][34][35]
Without the protection of Earth's
atmosphere and
magnetosphere astronauts are exposed to high levels of
radiation. A year in
low Earth orbit results in a dose of radiation 10 times that of the annual dose on earth.
[citation needed] 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,
[36] as the
health threat from cosmic rays significantly increases the chances of cancer over a decade or more of exposure.
[37] A
NASA-supported study reported that radiation may harm the
brain of
astronauts and accelerate the onset of
Alzheimer's disease.
[38][39][40][41] 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.
[42]
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 crew of
Expedition 10 took shelter as a precaution in 2005 in a more heavily shielded part of the station designed for this purpose.
[43][44] However, beyond the limited protection of Earth's
magnetosphere,
interplanetary manned 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.
[45]
A video made by the crew of the International Space Station showing the
Aurora Australis, which is caused by high-energy particles in the space environment.
There is scientific concern that extended spaceflight might slow down the body's ability to protect itself against diseases.
[46]
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 aberrations' in
lymphocytes. As these cells are central to the
immune system, any damage weakens the immune system, which means that in addition to increased vulnerability to new exposures,
viruses already present in the body—which would normally be suppressed—become active. In space,
T-cells
(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, The NASA scientists reported that a possible
manned mission to Mars[47] may involve a great
radiation risk based on the amount of
energetic particle radiation detected by the
RAD on the
Mars Science Laboratory while traveling from the
Earth to
Mars in 2011–2012.
[33][34][35]
In September 2017, NASA reported
radiation levels on the surface of the planet
Mars were temporarily
doubled, and were associated with an
aurora 25-times brighter than any observed earlier, due to a massive, and unexpected,
solar storm in the middle of the month.
[48]
Weightlessness
Astronauts on the
ISS in weightless conditions.
Michael Foale can be seen exercising in the foreground.
Following the advent of
space stations that can be inhabited for long periods of time, exposure to
weightlessness
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. Though these changes are usually temporary, some do have a long-term impact on human
health.
Short-term exposure to microgravity causes
space adaptation syndrome, a self-limiting nausea caused by derangement of the
vestibular system.
Long-term exposure causes multiple health problems, one of the most
significant being loss of bone and muscle mass. Over time these
deconditioning effects can impair astronauts' performance, increase their risk of injury, reduce their
aerobic capacity, and slow down their
cardiovascular system.
[49]
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.
[42] Redistributing fluids around the body itself causes balance disorders,
distorted vision, and a loss of taste and smell.
A 2006 Space Shuttle experiment found that
Salmonella typhimurium, a bacterium that can cause
food poisoning, became more virulent when cultivated in space.
[50] On April 29, 2013, scientists in Rensselaer Polytechnic Institute, funded by
NASA, reported that, during
spaceflight on the
International Space Station,
microbes seem to adapt to the
space environment in ways "not observed on Earth" and in ways that "can lead to increases in growth and
virulence".
[51] More recently, in 2017,
bacteria were found to be more resistant to
antibiotics and to thrive in the near-weightlessness of space.
[52] Microorganisms have been observed to survive the
vacuum of outer space.
[53][54]
Motion sickness
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, and arises as the
vestibular system adapts to weightlessness.
[55] Symptoms of SAS include
nausea and
vomiting,
vertigo,
headaches,
lethargy, and overall malaise.
[2] The first case of SAS was reported by
cosmonaut Gherman Titov
in 1961. Since then, roughly 45% of all people who have flown in space
have suffered from this condition. The duration of space sickness
varies, but rarely has it lasted for more than 72 hours, after which the
body adjusts to the new environment.
On Earth, our bodies react automatically to gravity, maintaining both
posture and locomotion in a downward pulling world. In microgravity
environments, these constant signals are absent: the
otolith organs in the inner
ear
are sensitive to linear acceleration and no longer perceive a downwards
bias; muscles are no longer required to contract to maintain posture,
and pressure receptors in the feet and ankles no longer signal the
direction of "down". These changes can immediately result in
visual-orientation illusions where the astronaut feels he has flipped
180 degrees. Over half of astronauts also experience symptoms of
motion sickness for the first three days of travel due to the conflict between what the body expects and what the body actually perceives.
[56]
Over time however the brain adapts and although these illusions can
still occur, most astronauts begin to see "down" as where the feet are.
People returning to Earth after extended weightless periods have to
readjust to the force of gravity and may have problems standing up,
focusing their gaze, walking and turning. This is just an initial
problem, as they recover these abilities quickly.
[vague]
NASA jokingly measures SAS using the "Garn scale", named for
United States Senator Jake Garn, whose sickness during
STS-51-D was the worst on record. Accordingly, one "Garn" is equivalent to the most severe possible case of space sickness.
[57]
By studying how changes can affect balance in the human body—involving
the senses, the brain, the inner ear, and blood pressure—NASA hopes to
develop treatments that can be used on Earth and in space to correct
balance disorders. Until then, astronauts rely on medication, such as
midodrine and
dimenhydrinate anti-nausea patches, as required (such as when
space suits are worn, because vomiting into a space suit could be fatal).
Bone and muscle deterioration
Aboard the International Space Station, astronaut
Frank De Winne is attached to the
COLBERT with bungee cords
A major effect of long-term weightlessness involves the loss of
bone and
muscle mass. Without the effects of gravity,
skeletal muscle
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
muscles
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
[58] The types of
muscle fibre
prominent in muscles also change. Slow twitch endurance fibres used to
maintain posture are replaced by fast twitch rapidly contracting fibres
that are insufficient for any heavy labour. Advances in research on
exercise, hormone supplements and medication may help maintain muscle
and body mass.
Bone
metabolism also changes. Normally, bone is laid down in the direction of
mechanical stress. However, in a microgravity environment there is very
little mechanical stress. This results in a
loss of bone tissue approximately 1.5% per month especially from the lower vertebrae, hip and femur.
[59]
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.
[60]
The rapid change in bone density is dramatic, making bones frail and
resulting in symptoms which 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.
[61]
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.
[62] Osteoblasts are not consecutively active with the osteoclasts, causing the bone to be constantly diminished with no recovery.
[63]
This increase in osteoclasts activity has been seen particularly in the
pelvic region, because this is the region which 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 levels from the lost bone result in dangerous calcification of soft tissues and potential
kidney stone formation.
[59]
It is still unknown whether bone recovers completely. Unlike people
with osteoporosis, astronauts eventually regain their bone density.
[citation needed] After a 3–4 month trip into space, it takes about 2–3 years to regain lost bone density.
[citation needed]
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 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,
[64] and a stationary bicycle; each astronaut spends at least two hours per day exercising on the equipment.
[65][66] Astronauts use bungee cords to strap themselves to the treadmill.
[67][68]
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.
[3]
Currently,
NASA
is using advanced computational tools to understand the how to best
counteract the bone and muscle atrophy experienced by astronauts in
microgravity environments for prolonged periods of time.
[69]
The Human Research Program's Human Health Countermeasures Element
chartered the Digital Astronaut Project to investigate targeted
questions about exercise countermeasure regimes.
[70][71] NASA is focusing on integrating a model of the advanced Resistive Exercise Device (ARED) currently on board the
International Space Station with
OpenSim [72]
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
The effects of microgravity on fluid distribution around the body (greatly exaggerated).
Astronaut
Clayton Anderson observes as a water bubble floats in front of him on the Discovery. Water
cohesion plays a bigger role in microgravity than on Earth
The second effect of weightlessness takes place in human fluids. The
body is made up of 60% water, much of it intra-vascular and
inter-cellular. Within a few moments of entering a microgravity
environment, fluid is immediately re-distributed to the upper body
resulting in bulging neck veins, puffy face and sinus and nasal
congestion which can last throughout the duration of the trip and is
very much like the symptoms of the common cold. In space the autonomic
reactions of the body to maintain blood pressure are not required and
fluid is distributed more widely around the whole body. This results in a
decrease in
plasma
volume of around 20%. These fluid shifts initiate a cascade of adaptive
systemic effects that can be dangerous upon return to earth.
Orthostatic intolerance
results in astronauts returning to Earth after extended space missions
being unable to stand unassisted for more than 10 minutes at a time
without fainting. This is due in part to changes in the autonomic
regulation of blood pressure and the loss of plasma volume. Although
this effect becomes worse the longer the time spent in space, as yet all
individuals have returned to normal within at most a few weeks of
landing.
[citation needed]
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.
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,
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 and other unwelcome side effects. Upon return to earth, the blood begins to pool in the lower extremities again, resulting in
orthostatic hypotension."
[73]
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.
[74] Noted changes included a flattening of the eyeball and changes to the retina.
[74] Space traveler's eye-sight can become blurry after too much time in space.
[75][76] Another effect is known as
Cosmic ray visual phenomena
...[a] NASA survey of 300 male and female astronauts, about 23
percent of short-flight and 49 percent of long-flight astronauts said
they had experienced problems with both near and distance vision during
their missions. Again, for some people vision problems persisted for
years afterward.
- Intracranial pressure
Because weightlessness increases the amount of fluid in the upper part of the body, astronauts experience increased
intracranial pressure. This appears to increase pressure on the backs of the eyeballs, affecting their shape and slightly crushing the
optic nerve.
[1][77][78][79][80][81] This effect was noticed in 2012 in a study using
MRI scans of astronauts who had returned to Earth following at least one month in space.
[82] Such eyesight problems could be a major concern for future deep space flight missions, including a
manned mission to the planet
Mars.
[47][77][78][79][80]
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.
[83]
Taste
One effect of weightlessness on humans is that some astronauts report a change in their sense of
taste when in space.
[84]
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,
[85]
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
After two months, calluses on the bottoms of feet
molt and fall off from lack of use, leaving soft new skin. Tops of feet become, by contrast, raw and painfully sensitive.
[86] Tears cannot be shed while crying, as they stick together into a ball.
[87] In microgravity odors quickly permeate the environment, and NASA found in a test that the smell of
cream sherry triggered the gag reflex.
[85]
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.
[88] These may be part of the
asthenization syndrome reported by
cosmonauts living in space over an extended period of time, but regarded as anecdotal by astronauts.
[89]
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 all the internal and external stress crews
in space must face.
[citation needed]
Astronauts may not be able to quickly return to Earth or receive
medical supplies, equipment or personnel if a medical emergency occurs.
The astronauts may have to rely for long periods on their limited
existing resources and medical advice from the ground.
Psychological effects
Studies of Russian cosmonauts, such as those on
Mir, provide data on the long-term effects of space on the human body.
Research
The psychological effects of living in space have not been clearly analyzed but analogies on Earth do exist, such as
Arctic research stations and
submarines.
The enormous stress on the crew, coupled with the body adapting to
other environmental changes, can result in anxiety, insomnia and
depression.
[90]
Stress
There has
been considerable evidence that psychosocial stressors are among the
most important impediments to optimal crew morale and performance.
[91] Cosmonaut
Valery Ryumin, 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 a eighteen
by twenty-foot cabin for a month. Human nature won't stand it."
[92]
NASA's interest in psychological stress caused by space travel,
initially studied when their manned 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's mother died in a car accident, and when
Michael Fincke was forced to miss the birth of his second child.
[citation needed]
Sleep
The amount and quality of
sleep
experienced in space is poor due to highly variable light and dark
cycles on flight decks and poor illumination during daytime hours in the
space craft. Even the habit of looking out of the window before
retiring can send the wrong messages to the brain, resulting in poor
sleep patterns. These disturbances in
circadian rhythm
have profound effects on the neurobehavioural responses of crew and
aggravate the psychological stresses they already experience. Sleep is disturbed on the
ISS
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;
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
astronauts take sleeping pills and still get 2 hours less sleep each
night in space than they do 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.
[93]
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.
[94]
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 a
crew 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
Space colonization efforts must take into account the effects of space on the human body.
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[47]
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 in 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.
Test beds 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 and more complex bioregenerative
life support systems may someday be capable of mitigating some risks.
, where Fγ(L) is the fluence of particles with LET=L, traversing the organ,
![q(E,a_{E},a)={\frac {M(a)+m(E,a_{E},a)}{1+{\frac {1}{2}}\left[M(a)+m(E,a_{E},a)\right]}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/4518a8b09c1f86bb627f173dc5d743b59bf837ab)
![S(E,a_{E},a)=\prod _{{u=a_{E}}}^{{a-1}}\left[1-q(E,a_{E},u)\right]](https://wikimedia.org/api/rest_v1/media/math/render/svg/7130183dbc3d154a69b8782aed4d919bdadf15e4)
![ELR=\sum _{{a=a_{E}}}^{\infty }\left[M(a)+m(E,a_{E},a)\right]S(E,a_{E},a)-\sum _{{a=a_{E}}}^{\infty }M(a)S(0,a_{E},a)](https://wikimedia.org/api/rest_v1/media/math/render/svg/ee601de8daa87f8a72fd39b01835b1f680b507e5)
represents the folding of predictions of tissue-weighted LET spectra
behind spacecraft shielding with the radiation mortality rate to form a
rate for trial J.
..
![m(E,a_{E},a)=\left[ERR(a_{E},a)M_{c}(a)+(1-v)EAR(a_{E},a)\right]{{\frac {\sum _{L}Q(L)F(L)L}{DDREF}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/515cc797e69fc722ecc2c98e29a2b10fbca4513f)
