Effect of spaceflight on the human body

From Wikipedia, the free encyclopedia

 

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

This painting, An Experiment on a Bird in the Air Pump depicts an experiment performed by Robert Boyle in 1660 to test the effect of a vacuum on a living system.

Human physiology is adapted to living within the atmosphere of Earth, and a certain amount of oxygen is required in the air we breathe. If the body does not get enough oxygen, then the astronaut is at risk of becoming unconscious and dying from hypoxia. In the vacuum of space, gas exchange in the lungs continues as normal but results in the removal of all gases, including oxygen, from the bloodstream. After 9 to 12 seconds, the deoxygenated blood reaches the brain, and it results in the loss of consciousness.^[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]

Play media

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

Bruce McCandless floating free in orbit with a space suit and Manned Maneuvering Unit.

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.

— NASA^[74]

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.

Mars to Stay

From Wikipedia, the free encyclopedia

Concept for NASA Design Reference Mission Architecture 5.0 (2009)

Mars to Stay missions propose astronauts sent to Mars for the first time should intend to stay. Unused emergency return vehicles would be recycled into settlement construction as soon as the habitability of Mars becomes evident to the initial pioneers. Mars to Stay missions are advocated both to reduce cost and to ensure permanent settlement of Mars. Among many notable Mars to Stay advocates, former Apollo astronaut Buzz Aldrin has been particularly outspoken, suggesting in numerous forums "Forget the Moon, Let’s Head to Mars!"^[1] and, in June 2013, Aldrin promoted a manned mission "to homestead Mars and become a two-planet species".^[2] In August 2015, Aldrin, in association with the Florida Institute of Technology, presented a "master plan", for NASA consideration, for astronauts, with a "tour of duty of ten years", to colonize Mars before the year 2040.^[3] The Mars Underground, Mars Homestead Foundation, Mars One, and Mars Artists Community advocacy groups and business organizations have also adopted Mars to Stay policy initiatives.^[4]

The earliest formal outline of a Mars to Stay mission architecture was given at the Case for Mars VI Workshop in 1996, during a presentation by George Herbert titled "One Way to Mars".^[5]

Proposals

Arguments for settlement missions

Since returning the astronauts from the surface of Mars is one of the most difficult parts of a Mars mission, the idea of a one-way trip to Mars has been proposed several times. Space activist Bruce Mackenzie, for example, proposed a one-way trip to Mars in a presentation "One Way to Mars – a Permanent Settlement on the First Mission" at the 1998 International Space Development Conference,^[6] arguing that since the mission could be done with less difficulty and expense if the astronauts were not required to return to Earth, the first mission to Mars should be a settlement, not a visit.

Paul Davies, writing in the New York Times in 2004, made similar arguments.^[7] Under Davies' plan, an initial colony of four astronauts equipped with a small nuclear reactor and a couple of rover vehicles would make their own oxygen, grow food, and even initiate building projects using local raw materials. Supplemented by food shipments, medical supplies, and replacement gadgets from Earth, the colony would be indefinitely sustained.

Original Aldrin plan

Under Mars to Stay mission architectures, the first humans to travel to Mars would typically be in six-member teams. After this initial landing, subsequent missions would raise the number of persons on Mars to 30, thereby beginning a Martian settlement. Since the Martian surface offers all the natural resources and elements necessary to sustain a robust, mature, industrialized human settlement^[8]—unlike, for example the Moon^[9]—a permanent Martian settlement is thought to be the most effective way to ensure that humanity becomes a space-faring, multi-planet species.^[10] Through the use of digital fabricators and in vitro fertilisation it is assumed a permanent human settlement on Mars can grow organically from an original thirty to forty pioneers.^[11]

A Mars to Stay mission following Aldrin's proposal would enlist astronauts in the following timeline:

• Age 30: an offer to help settle Mars is extended to select pioneers
• Age 30–35: training and social conditioning for long-duration isolation and time-delay communications
• Age 35: launch three married couples to Mars; followed in subsequent years by a dozen or more couples
• Age 35–65: development of sheltered underground living spaces; artificial insemination ensures genetic diversity
• Age 65: an offer to return to Earth or retire on Mars is given to first-generation settlers

As Aldrin has said, "who knows what advances will have taken place. The first generation can retire there, or maybe we can bring them back."^[11]

"To Boldly Go: A One-Way Human Mission to Mars"

An article by Dirk Schulze-Makuch (Washington State University) and Paul Davies (Arizona State University) from the book The Human Mission to Mars: Colonizing the Red Planet^[12] highlights their mission plans as:

• No base on the Moon is needed. Given the broad variety of resources available on Mars, the long-term survival of Martian settlers is much more feasible than Lunar settlers.
• Since Mars affords neither an ozone shield nor magnetospheric protection, robots would prepare a basic modular base inside near-surface lava tubes and ice caves for the human settlers.
• A volunteer signing up for a one-way mission to Mars would do so with the full understanding that they will not return to Earth; Mars exploration would proceed for a long time on the basis of outbound journeys only.
• The first human contingent would consist of a crew of four, ideally (if budget permits) distributed between two two-man spacecraft for mission redundancy.
• Over time humans on Mars will increase with follow-up missions. Several subsurface biospheres would be created until there were 150+ individuals in a viable gene pool. Genetic engineering would further contribute to the health and longevity of settlers.

The astronauts would be sent supplies from Earth regularly. This proposal was picked up for discussion in a number of public sources.^[13]

Mars One

A proposal for a one-way human settlement mission to Mars was put forward in 2012 by the Mars One, a private spaceflight project led by Dutch entrepreneur Bas Lansdorp to establish a permanent human colony on Mars.^[14] Mars One is a Dutch not-for-profit foundation, a Stichting.^[15][16] The proposal is to send a communication satellite and path finder lander to the planet by 2018 and, after several stages, land four humans on Mars for permanent settlement in 2027.^[17] A new set of four astronauts would then arrive every two years.^[18] 200,000 applications were started; about 2,500 were complete enough for consideration, from which one hundred applicants have been chosen so far. Further selections are planned to narrow this down to six groups of four before training begins in 2016.^{[19][needs update]} It is hoped their reality television show, participant fees, and donations will generate the funding for the project.^[20]

The project has been criticized by experts as a 'scam'^{[21][22][23][24][25]} and as 'delusional'.^{[26][27][20][28]}

Strive to Stay: Emergency Return Only

In response to feedback following the EarthLight Institute's "Mars Colony 2030" project at NewSpace 2012 and the announcement of Mars One, Eric Machmer proposed conjunction-class missions be planned with a bias to stay (if low gravity, radiation, and other factors present no pressing health issues),^[29][30] so that, if at the end of each 550-day period during a conjunction-class launch window no adverse health effects were observed, settlers would continue research and construction through another 550-day period. In the meantime, additional crews and supplies would continue to arrive, starting their own 550-day evaluation periods. Health tests would be repeated during subsequent 550-day periods until the viability of human life on Mars was proven. Once settlers determine that humans can live on Mars without negative health effects, emergency return vehicles would be recycled into permanent research bases.

Initial and permanent settlement

Initial explorers leave equipment in orbit and at landing zones scattered considerable distances from the main settlement. Subsequent missions therefore are assumed to become easier and safer to undertake, with the likelihood of back-up equipment being present if accidents in transit or landing occur.

Large subsurface, pressurized habitats would be the first step toward human settlement; as Dr. Robert Zubrin suggests in the first chapter of his book Mars Direct, these structures can be built as Roman-style atria in mountainsides or underground with easily produced Martian brick. During and after this initial phase of habitat construction, hard-plastic radiation and abrasion-resistant geodesic domes could be deployed on the surface for eventual habitation and crop growth. Nascent industry would begin using indigenous resources: the manufacture of plastics, ceramics and glass could be easily achieved.

The longer-term work of terraforming Mars requires an initial phase of global warming to release atmosphere from the Martian regolith and to create a water-cycle. Three methods of global warming are described by Zubrin, who suggests they are best deployed in tandem: orbital mirrors to heat the surface; factories on the ground to pump halocarbons into the atmosphere; and the seeding of bacteria that can metabolize water, nitrogen and carbon to produce ammonia and methane (these gases would aid in global warming). While the work of terraforming Mars is on-going, robust settlement of Mars would continue.

Zubrin, in his 1996 book (revised 2011) The Case for Mars, acknowledges any Martian colony will be partially Earth-dependent for centuries. However, Zubrin suggests Mars may be profitable for two reasons. First, it may contain concentrated supplies of metals equal to or of greater value than silver, which have not been subjected to millennia of human scavenging; it is suggested such ores may be sold on Earth for profit. Secondly, the concentration of deuterium—an extremely expensive but essential fuel for the as-yet non-existent nuclear fusion power industry—is five times greater on Mars. Humans emigrating to Mars, under this paradigm, are presumed to have an industry; it is assumed the planet will be a magnet for settlers as wage costs will be high. Because of the labor shortage on Mars and its subsequent high pay-scale, Martian civilization and the value placed upon each individual's productivity is proposed as a future engine of both technological and social advancement.

Risks

Artist's conception of a human mission on Mars
1989 painting by Les Bossinas of Lewis Research Center for NASA

In the fifth chapter of "Mars Direct", Zubrin addresses the idea that radiation and zero-gravity are unduly hazardous. He claims cancer rates do increase for astronauts who have spent extensive time in space, but only marginally. Similarly, while zero-gravity presents challenges, near total recovery of musculature and immune system vitality is presumed by all Mars to Stay mission plans once settlers are on the Martian surface. Several experiments, such as the Mars Gravity Biosatellite, have been proposed to test this hypothetical assumption, but until humans have lived in Martian gravity conditions (38% of Earth's), human long-term viability in such low gravity will remain only a working assumption. Back-contamination—humans acquiring and spreading hypothetical Martian viruses—is described as "just plain nuts", because there are no host organisms on Mars for disease organisms to have evolved.

In the same chapter, Zubrin rejects suggestions the Moon should be used as waypoint to Mars or as a preliminary training area. "It is ultimately much easier to journey to Mars from low Earth orbit than from the Moon and using the latter as a staging point is a pointless diversion of resources." While the Moon may superficially appear a good place to perfect Mars exploration and habitation techniques, the two bodies are radically different. The Moon has no atmosphere, no analogous geology and a much greater temperature range and rotational period of illumination. It is argued Antarctica, deserts of Earth, and precisely controlled chilled vacuum chambers on easily accessible NASA centers on Earth provide much better training grounds at lesser cost.

Public reception

Artist's conception of a Mars Habitat
1993 by John Frassanito and Associates for NASA

"Should the United States space program send a mission to Mars, those astronauts should be prepared to stay there," said Lunar astronaut Buzz Aldrin during an interview on "Mars to Stay" initiative.^[31] The time and expense required to send astronauts to Mars, argues Aldrin, "warrants more than a brief sojourn, so those who are on board should think of themselves as pioneers. Like the Pilgrims who came to the New World or the families who headed to the Wild West, they should not plan on coming back home." The Moon is a shorter trip of two or three days, but according to Mars advocates it offers virtually no potential for independent settlements. Studies have found that Mars, on the other hand, has vast reserves of frozen water, all of the basic elements, and more closely mimics both gravitational (roughly ​¹⁄₃ of Earth's while the moon is ​¹⁄₆) and illumination conditions on Earth. "It is easier to subsist, to provide the support needed for people there than on the Moon." In an interview with reporters, Aldrin said Mars offers greater potential than Earth's satellite as a place for habitation:

If we are going to put a few people down there and ensure their appropriate safety, would you then go through all that trouble and then bring them back immediately, after a year, a year and a half? ... They need to go there more with the psychology of knowing that you are a pioneering settler and you don't look forward to go back home again after a couple of years.^[32]

A comprehensive statement of a rationale for "Mars to Stay" was laid out by Dr. Aldrin in a May 2009 Popular Mechanics article, as follows:

The agency's current Vision for Space Exploration will waste decades and hundreds of billions of dollars trying to reach the Moon by 2020—a glorified rehash of what we did 40 years ago. Instead of a steppingstone to Mars, NASA's current lunar plan is a detour. It will derail our Mars effort, siphoning off money and engineering talent for the next two decades. If we aspire to a long-term human presence on Mars—and I believe that should be our overarching goal for the foreseeable future—we must drastically change our focus. Our purely exploratory efforts should aim higher than a place we've already set foot on six times. In recent years my philosophy on colonizing Mars has evolved. I now believe that human visitors to the Red Planet should commit to staying there permanently. One-way tickets to Mars will make the missions technically easier and less expensive and get us there sooner. More importantly, they will ensure that our Martian outpost steadily grows as more homesteaders arrive. Instead of explorers, one-way Mars travelers will be 21st-century pilgrims, pioneering a new way of life. It will take a special kind of person. Instead of the traditional pilot/scientist/engineer, Martian homesteaders will be selected more for their personalities—flexible, inventive and determined in the face of unpredictability. In short, survivors.^[33]

The Mars Artists Community has adopted Mars to Stay as their primary policy initiative.^[34] During a 2009 public hearing of the U.S. Human Space Flight Plans Committee at which Dr. Robert Zubrin presented a summary of the arguments in his book The Case for Mars, dozens of placards reading "Mars Direct Cowards Return to the Moon" were placed throughout the Carnegie Institute.^[35] The passionate uproar among space exploration advocates—both favorable and critical—resulted in the Mars Artists Community creating several dozen more designs, with such slogans as, "Traitors Return to Earth" and "What Would Zheng He Do?"

Mars Artists design, August 2009.

In October 2009, Eric Berger of the Houston Chronicle wrote of "Mars to Stay" as perhaps the only program that can revitalize the United States' space program:

What if NASA could land astronauts on Mars in a decade, for not ridiculously more money than the $10 billion the agency spends annually on human spaceflight? It's possible ... relieving NASA of the need to send fuel and rocketry to blast humans off the Martian surface, which has slightly more than twice the gravity of the moon, would actually reduce costs by about a factor of 10, by some estimates.^[36]

Hard Science Fiction writer Mike Brotherton has found "Mars to Stay" appealing for both economic and safety reasons, but more emphatically, as a fulfillment of the ultimate mandate by which "our manned space program is sold, at least philosophically and long-term, as a step to colonizing other worlds". Two-thirds of the respondents to a poll on his website expressed interest in a one-way ticket to Mars "if mission parameters are well-defined" (not suicidal).^[37]

In June 2010, Buzz Aldrin gave an interview to Vanity Fair in which he restated "Mars to Stay":

Did the Pilgrims on the Mayflower sit around Plymouth Rock waiting for a return trip? They came here to settle. And that's what we should be doing on Mars. When you go to Mars, you need to have made the decision that you're there permanently. The more people we have there, the more it can become a sustaining environment. Except for very rare exceptions, the people who go to Mars shouldn't be coming back. Once you get on the surface, you're there.^[38]

An article by Dirk Schulze-Makuch (Washington State University) and Paul Davies (Arizona State University) from the book The Human Mission to Mars: Colonizing the Red Planet^[12] summarizes their rationale for Mars to Stay:

[Mars to stay] would obviate the need for years of rehabilitation for returning astronauts, which would not be an issue if the astronauts were to remain in the low-gravity environment of Mars. We envision that Mars exploration would begin and proceed for a long time on the basis of outbound journeys only.^[12]

In November 2010, Keith Olbermann started an interview with Derrick Pitts, Planetarium Director at the Franklin Institute in Philadelphia, by quoting from the Dirk Schulze-Makuch and Paul Davies article, saying, "The Astronauts would go to Mars with the intention of staying for the rest of their lives, as trailblazers of a permanent human Mars colony." In response to Olbermann's statement that "the authors claim a one-way ticket to Mars is no more outlandish than a one-way ticket to America was in 1620", Pitts defends Mars to Stay initiatives by saying "they begin to open the doors in a way that haven't been opened before".^[39]

In a January 2011 interview, X Prize founder Peter Diamandis expressed his preference for Mars to Stay research settlements:

Privately funded missions are the only way to go to Mars with humans because I think the best way to go is on "one-way" colonization flights and no government will likely sanction such a risk. The timing for this could well be within the next 20 years. It will fall within the hands of a small group of tech billionaires who view such missions as the way to leave their mark on humanity.^[40]

In March 2011, Apollo 14 pilot Edgar Mitchell and Apollo 17's geologist Harrison Schmitt, among other noted Mars exploration advocates published an anthology of Mars to Stay architectures titled, A One Way Mission to Mars: Colonizing the Red Planet". From the publisher's review:

Answers are provided by a veritable who's who of the top experts in the world. And what would it be like to live on Mars? What dangers would they face? Learn first hand, in the final, visionary chapter about life in a Martian colony, and the adventures of a young woman, Aurora, who is born on Mars. Exploration, discovery, and journeys into the unknown are part of the human spirit. Colonizing the cosmos is our destiny. The Greatest Adventure in the History of Humanity awaits us. Onward to Mars!^[41]

August 2011, Professor Paul Davies gave a plenary address to the opening session of the 14th Annual International Mars Society Convention on cost-effective human mission plans for Mars titled "One-Way Mission to Mars".^[42]

New York Times op-eds

"Mars to Stay" has been explicitly proposed by two op-ed pieces in the New York Times.^[7][43]

Following a similar line of argument to Buzz Aldrin, Lawrence Krauss asks in an op-ed, "Why are we so interested in bringing the Mars astronauts home again?".^[43] While the idea of sending astronauts aloft never to return may be jarring upon first hearing, the rationale for one-way exploration and settlement trips has both historical and practical roots. For example, colonists and pilgrims seldom set off to the New World with the expectation of a return trip. As Lawrence Krauss writes, "To boldly go where no one has gone before does not require coming home again."

If it sounds unrealistic to suggest that astronauts would be willing to leave home never to return ... consider the results of several informal surveys I and several colleagues have conducted recently. One of my peers in Arizona recently accompanied a group of scientists and engineers from the Jet Propulsion Laboratory on a geological survey. He asked how many would be willing to go on a one-way mission into space. Every member of the group raised their hand.^[43]

Additional immediate and pragmatic reasons to consider one-way human space exploration missions are explored by Krauss. Since much of the cost of a voyage to Mars will be spent on returning to Earth, if the fuel for the return is carried on board, this greatly increases the mission mass requirement – that in turn requires even more fuel. According to Krauss, "Human space travel is so expensive and so dangerous ... we are going to need novel, even extreme solutions if we really want to expand the range of human civilization beyond our own planet." Delivering food and supplies to pioneers via unmanned spacecraft is less expensive than designing an immediate return trip.

In an earlier 2004 op-ed for the New York Times, Paul Davies says motivation for the less expensive, permanent "one-way to stay option" arises from a theme common in "Mars to Stay" advocacy: "Mars is one of the few accessible places beyond Earth that could have sustained life [... and] alone among our sister planets, it is able to support a permanent human presence."^[7]

Why is going to Mars so expensive? ... It takes a lot of fuel to blast off Mars and get back home. If the propellant has to be transported there from Earth, costs of a launching soar.
Without some radical improvements in technology, the prospects for sending astronauts on a round-trip to Mars any time soon are slim, whatever the presidential rhetoric. What's more, the president's suggestion of using the Moon as a base — a place to assemble equipment and produce fuel for a Mars mission less expensively — has the potential to turn into a costly sideshow. There is, however, an obvious way to slash the costs and bring Mars within reach of early manned exploration. The answer lies with a one-way mission.^[7]

Davies argues that since "some people gleefully dice with death in the name of sport or adventure [and since] dangerous occupations that reduce life expectancy through exposure to hazardous conditions or substances are commonplace", we ought to not find the risks involved in a Mars to Stay architecture unusual. "A century ago, explorers set out to trek across Antarctica in the full knowledge that they could die in the process, and that even if they succeeded their health^[29] might be irreversibly harmed. Yet governments and scientific societies were willing sponsors of these enterprises." Davies then asks, "Why should it be different today?"^[7]

In situ resource utilization

From Wikipedia, the free encyclopedia

ISRU reverse water gas shift testbed (NASA KSC)

In space exploration, in situ resource utilization (ISRU) is defined as "the collection, processing, storing and use of materials encountered in the course of human or robotic space exploration that replace materials that would otherwise be brought from Earth."^[1] ISRU is the practice of leveraging resources found or manufactured on other astronomical objects (the Moon, Mars, asteroids, etc.) to fulfill or enhance the requirements and capabilities of a space mission.

ISRU can provide materials for life support, propellants, construction materials, and energy to a spacecraft payloads or space exploration crews. It is now very common for spacecraft and robotic planetary surface mission to harness the solar radiation found in situ in the form of solar panels. The use of ISRU for material production has not yet been implemented in a space mission, though several field tests in the late 2000s demonstrated various lunar ISRU techniques in a relevant environment.^[2]

ISRU has long been considered as a possible avenue for reducing the mass and cost of space exploration architectures, in that it may be a way to drastically reduce the amount of payload that must be launched from Earth in order to explore a given planetary body. According to NASA, "in-situ resource utilisation will enable the affordable establishment of extraterrestrial exploration and operations by minimizing the materials carried from Earth."^[3]

Uses

Water

In the context of ISRU water is most often sought directly as fuel or as feedstock for fuel production. Applications include its use in life support either directly by drinking, for growing food, producing oxygen, or numerous other industrial processes. All of which require a ready supply of water in the environment and the equipment to extract it. Such extraterrestrial water has been discovered in a variety of forms throughout the solar system, and a number of potential water extraction technologies have been investigated. For water that is chemically bound to regolith, solid ice, or some manner of permafrost, sufficient heating can recover the water. However this is not as easy as it appears because ice and permafrost can often be harder than plain rock, necessitating laborious mining operations. Where there is some level of atmosphere, such as on Mars, water can be extracted directly from the air using a simple process such as WAVAR. Another possible source of water is deep aquifers kept warm by Mars's latent geological heat, which can be tapped to provide both water and geothermal power.

Rocket propellant

Rocket propellant from water ice has also been proposed for the Moon, mainly from ice that has been found at the poles. The likely difficulties include working at extremely low temperatures and extraction from the regolith. Most schemes electrolyse the water and form hydrogen and oxygen and liquify and cryogenically store them. This requires large amounts of equipment and power to achieve. Alternatively it is possible to simply heat the water in a nuclear or solar thermal rocket,^[4] which seems to give very much more mass delivered to low Earth orbit (LEO) in spite of the much lower specific impulse, for a given amount of equipment.^[5]

The monopropellant hydrogen peroxide (H₂O₂) can be made from water on Mars and the Moon.^[6]

Aluminum as well as other metals have been proposed for use as rocket propellant made using lunar resources,^[7] and proposals include reacting the aluminum with water.^[8] For Mars, methane propellant can be manufactured via the Sabatier process.

Solar cell production

It has long been suggested that solar cells could be produced from the materials present in lunar soil. Silicon, aluminium, and glass, three of the primary materials required for solar cell production, are found in high concentrations in lunar soil and can be utilised to produce solar cells.^[9] In fact, the native vacuum on the lunar surface provides an excellent environment for direct vacuum deposition of thin-film materials for solar cells.^[10]

Solar arrays produced on the lunar surface can be used to support lunar surface operations as well as satellites off the lunar surface. Solar arrays produced on the lunar surface may prove more cost effective than solar arrays produced and shipped from Earth, but this trade depends heavily on the location of the particular application in question.

Another potential application of lunar-derived solar arrays is providing power to Earth. In its original form, known as the solar power satellite, the proposal was intended as an alternate power source for Earth. Solar cells would be shipped to Earth orbit and assembled, the power being transmitted to Earth via microwave beams.^[11] Despite much work on the cost of such a venture, the uncertainty lay in the cost and complexity of fabrication procedures on the lunar surface.

Metals for construction or return to Earth

Asteroid mining could also involve extraction of metals for construction material in space, which may be more cost-effective than bringing such material up out of Earth's deep gravity well, or that of any other large body like the Moon or Mars. Metallic asteroids contain huge amounts of siderophilic metals, including precious metals.

Building materials

The colonisation of planets or moons will require to obtain local building materials, such as regolith. For example, studies employing artificial Mars soil mixed with epoxy resin and tetraethoxysilane, produce high enough values of strength, resistance, and flexibility parameters.^[12]

Locations

Mars

ISRU research for Mars is focused primarily on providing rocket propellant for a return trip to Earth — either for a manned or a sample return mission — or for use as fuel on Mars. Many of the proposed techniques utilise the well-characterised atmosphere of Mars as feedstock. Since this can be easily simulated on Earth, these proposals are relatively simple to implement, though it is by no means certain that NASA or the ESA will favour this approach over a more conventional direct mission.^[13]

A typical proposal for ISRU is the use of a Sabatier reaction, CO₂ + 4H₂ → CH₄ + 2H₂O, in order to produce methane on the Martian surface, to be used as a propellant. Oxygen is liberated from the water by electrolysis, and the hydrogen recycled back into the Sabatier reaction. The usefulness of this reaction is that—as of 2008, when the availability of water on Mars was less scientifically demonstrated—only the hydrogen (which is light) was thought to need to be brought from Earth.^[14]

As of 2016, SpaceX is currently developing the technology for a Mars propellant plant that will use a variation on what is described in the previous paragraph. Rather than transporting hydrogen from Earth to use in making the methane and oxygen, they intend to mine the requisite water from subsurface water ice that is now known to be abundant across much of the Martian surface, produce and then store the post-Sabatier reactants, and then use it as propellant for return flights of their Interplanetary Spaceship no earlier than 2023.^[15][16]

A similar reaction proposed for Mars is the reverse water gas shift reaction, CO₂ + H₂ → CO + H₂O. This reaction takes place rapidly in the presence of an iron-chrome catalyst at 400 Celsius,^[17] and has been implemented in an Earth-based testbed by NASA.^[18] Again, oxygen is recycled from the water by electrolysis, and the reaction only needs a small amount of hydrogen from Earth. The net result of this reaction is the production of oxygen, to be used as the oxidizer component of rocket fuel.

Another reaction proposed for the production of oxygen and fuel^[19] is the electrolysis of the atmospheric carbon dioxide,

${\displaystyle {\ce {{\overset {atmospheric \atop {carbon\ dioxide}}{2CO2}}->[energy]{2CO}+O2}}}$.^[20]

More recently, it has been proposed the in situ production of oxygen, hydrogen and CO from the martian hematite deposits via a two-step thermochemical CO₂/H₂O splitting process, and specifically in the magnetite/wustite redox cycle.^[21] Although thermolysis is the most direct, one-step process for splitting molecules, it is neither practical nor efficient in the case of either H₂O or CO₂. This is because the process requires a very high temperature (> 2500 C) to achieve a meaningful dissociation fraction.^[22] This poses problems in finding suitable reactor materials, losses due to vigorous product recombination, and excessive aperture radiation losses when concentrated solar heat is used. The magnetite/wustite redox cycle was first proposed for solar application on earth by Nakamura,^[23] and was one of the first used for solar-driven two-step water splitting. In this cycle, water reacts with wustite (FeO) to form magnetite (Fe₃O₄) and hydrogen. The summarised reactions in this two-step splitting process are as follows:

${\displaystyle {\ce {Fe3O4->[energy]{3FeO}+\overbrace {1/2O2} ^{\underset {(\operatorname {by-product} )}{oxygen}}}}}$.

and the obtained FeO is used for the thermal splitting of water or CO₂ :

3FeO + H₂O → Fe₃O₄ + H₂

3FeO + CO₂ → Fe₃O₄ + CO

This process is repeated cyclically. The above process results in a substantial reduction in the thermal input of energy if compared with the most direct, one-step process for splitting molecules.^[24]

However, the process needs wustite (Fe₃O₄) to start the cycle, but on Mars there is no wustite or at least not in significant amounts. Nevertheless, wustite can be easily obtained by reduction of hematite (Fe₂O₃) which is an abundant material on Mars, being specially conspicuous the strong hematite deposits located at Terra Meridiani.^[25] The intention of wustite from the hematite -abundantly available on Mars, is an industrial process well-known on earth, and us performed by the following two main reduction reactions, namely:

3Fe₂O₃ + H₂ → 2Fe₃O₄ + H₂O

3Fe₂O₃ + CO → 2Fe₃O₄ + CO₂

Mars Surveyor 2001 Lander MIP (Mars ISPP Precursor) was to demonstrate manufacture of oxygen from the atmosphere of Mars,^[26] and test solar cell technologies and methods of mitigating the effect of Martian dust on the power systems.^[27] The proposed Mars 2020 rover mission might include ISRU technology demonstrator that would extract CO₂ from the atmosphere and produce O₂ for rocket fuel.^[28]

It has been suggested that buildings on Mars could be made from basalt as it has good insulating properties. An underground structure of this type would be able to protect life forms against radiation exposure.^[29]

All of the resources required to make plastics exist on Mars.^[30][31] Many of these complex reactions are able to be completed from the gases harvested from the martian atmosphere. Traces of free oxygen, carbon monoxide, water and methane are all known to exist.^[32][33] Hydrogen and oxygen can be made by the electrolysis of water, carbon monoxide and oxygen by the electrolysis of carbon dioxide and methane by the Sabatier reaction of carbon dioxide and hydrogen. These basic reactions provide the building blocks for more complex reaction series which are able to make plastics.  Ethylene is used to make plastics such as polyethylene and polypropylene and can be made from carbon monoxide and hydrogen,^[34]

2CO + 4H₂ → C₂H₄ + 2H₂O.

Moon

Footprint in lunar regolith.

The Moon possesses abundant raw materials that are potentially relevant to a hierarchy of future applications, beginning with the use of lunar materials to facilitate human activities on the Moon itself and progressing to the use of lunar resources to underpin a future industrial capability within the Earth-Moon system.^[35]

The lunar highland material anorthite can be used as aluminium ore. Smelters can produce pure aluminium, calcium metal, oxygen and silica glass from anorthite. Raw anorthite is also good for making fiberglass and other glass and ceramic products.^[36] One particular processing technique is to use fluorine brought from Earth as potassium fluoride to separate the raw materials from the lunar rocks.^[37]

Over twenty different methods have been proposed for oxygen extraction on the Moon.^[7] Oxygen is often found in iron rich lunar minerals and glasses as iron oxide. The oxygen can be extracted by heating the material to temperatures above 900 °C and exposing it to hydrogen gas. The basic equation is: FeO + H₂ → Fe + H₂O. This process has recently been made much more practical by the discovery of significant amounts of hydrogen-containing regolith near the Moon's poles by the Clementine spacecraft.^[38]

Lunar materials may also be valuable for other uses. It has also been proposed to use lunar regolith as a general construction material,^[39] through processing techniques such as sintering, hot-pressing, liquification, and the cast basalt method. Cast basalt is used on Earth for construction of, for example, pipes where a high resistance to abrasion is required. Cast basalt has a very high hardness of 8 Mohs (diamond is 10 Mohs) but is also susceptible to mechanical impact and thermal shock^[40] which could be a problem on the Moon.

Glass and glass fiber are straightforward to process on the Moon and Mars, and it has been argued that the glass is optically superior to that made on the Earth because it can be made anhydrous.^[36] Successful tests have been performed on Earth using two lunar regolith simulants MLS-1 and MLS-2.^[41] Basalt fibre has also been made from lunar regolith simulators.

In August 2005, NASA contracted for the production of 16 tonnes of simulated lunar soil, or "Lunar Regolith Simulant Material."^[42] This material is now commercially available for research on how lunar soil could be utilized in situ.^[43]

Martian moons, Ceres, asteroids

Other proposals^[44] are based on Phobos and Deimos. These moons are in reasonably high orbits above Mars, have very low escape velocities, and unlike Mars have return delta-v's from their surfaces to LEO which are less than the return from the Moon.

Ceres is further out than Mars, with a higher delta-v, but launch windows and travel times are better, and the surface gravity is just 0.028 g, with a very low escape velocity of 510 m/s. Researchers have speculated that the interior configuration of Ceres includes a water-ice-rich mantle over a rocky core.^[45]

Near Earth Asteroids and bodies in the asteroid belt could also be sources of raw materials for ISRU.

Planetary atmospheres

Proposals have been made for "mining" for rocket propulsion, using what is called a Propulsive Fluid Accumulator. Atmospheric gases like oxygen and argon could be extracted from the atmosphere of planets like the Earth, Mars, and the outer Gas Giants by Propulsive Fluid Accumulator satellites in low orbit.^[46]

ISRU capability classification (NASA)

In October 2004, NASA’s Advanced Planning and Integration Office commissioned an ISRU capability roadmap team. The team's report, along with those of 14 other capability roadmap teams, were published May 22, 2005.^[47] The report identifies seven ISRU capabilities:^[47]:278 (i) resource extraction, (ii) material handling and transport, (iii) resource processing, (iv) surface manufacturing with in situ resources, (v) surface construction, (vi) surface ISRU product and consumable storage and distribution, and (vii) ISRU unique development and certification capabilities.

The report focuses on lunar and martian environments. It offers a detailed timeline^[47]:274 and capability roadmap to 2040^[47]:280-281 but it assumes lunar landers in 2010 and 2012.^[47]:280

ISRU technology demonstrators and prototypes

The Mars Surveyor 2001 Lander was intended to carry to Mars a test payload, MIP (Mars ISPP Precursor), that was to demonstrate manufacture of oxygen from the atmosphere of Mars,^[48] but the mission was cancelled.

The Mars Oxygen ISRU Experiment (MOXIE) is a 1% scale prototype model aboard the planned Mars 2020 rover that will produce oxygen from Martian atmospheric carbon dioxide (CO₂) in a process called solid oxide electrolysis.^{[49][50][51][52]}