Effect of spaceflight on the human body

Common questions

What brain changes occur in astronauts after spaceflight?

Significant changes in the position and structure of the brain have been found in astronauts who have taken trips in space. These findings came from MRI studies comparing crew members after their missions. Astronauts who took longer space trips were associated with greater brain changes than those on shorter flights.

How does weightlessness affect astronaut eyesight and vision?

Redistributing fluids around the body causes balance disorders and distorted vision which leads to a loss of taste and smell for many crew members. Noted changes included a flattening of the eyeball and changes to the retina that can make space travelers' eyesight blurry after too much time in space. This condition contributes to observations of altered speech motor control in astronauts.

Why do astronauts lose bone density during long spaceflights?

In a microgravity environment there is very little mechanical stress which results in a loss of bone tissue approximately 1.5% per month especially from the lower vertebrae hip and femur. There is an increase in osteoclast activity due to microgravity causing the bone to be constantly diminished with no recovery. The rapid change in bone density is dramatic making bones frail and resulting in symptoms that resemble those of osteoporosis.

What radiation risks do astronauts face outside Earth's magnetosphere?

High levels of radiation damage lymphocytes cells heavily involved in maintaining the immune system and contribute to the lowered immunity experienced by astronauts. Galactic cosmic rays present further challenges to human spaceflight as the health threat from cosmic rays significantly increases the chances of cancer over a decade or more of exposure. Solar flare events though rare can give a fatal radiation dose in minutes.

How does vacuum exposure affect human physiology and consciousness?

The only humans known to have died of exposure to vacuum in space are the three crew-members of the Soyuz 11 spacecraft who perished during preparations for re-entry from orbit on the 30th of June 1971. Jim LeBlanc remained conscious for about 14 seconds before losing consciousness due to hypoxia when his suit pressure dropped in less than 10 seconds. As he stumbled backwards he could feel the saliva on his tongue starting to bubble just before he went unconscious.

Bones Break And Muscles Fade

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 without regular exercise. Astronauts can lose up to 20% of their muscle mass in just five to eleven days. The types of muscle fiber prominent in muscles also change during this process. Slow-twitch endurance fibers used to maintain posture are replaced by fast-twitch rapidly contracting fibers that are insufficient for any heavy labor. Bone metabolism also changes when gravity disappears. Normally bone is laid down in the direction of mechanical stress. However in a microgravity environment there is very little mechanical stress. This results in a loss of bone tissue approximately 1.5% per month especially from the lower vertebrae hip and femur. Due to microgravity and the decreased load on the bones there is a rapid increase in bone loss from three percent cortical bone loss per decade to about one percent every month the body is exposed to microgravity for an otherwise healthy adult. The rapid change in bone density is dramatic making bones frail and resulting in symptoms that resemble those of osteoporosis. On Earth the bones are constantly being shed and regenerated through a well-balanced system which involves signaling of osteoblasts and osteoclasts. These systems are coupled so that whenever bone is broken down newly formed layers take its place neither should happen without the other in a healthy adult. In space however there is an increase in osteoclast activity due to microgravity. This is a problem because osteoclasts break down the bones into minerals that are reabsorbed by the body. Osteoblasts are not consecutively active with the osteoclasts causing the bone to be constantly diminished with no recovery. This increase in osteoclasts activity has been seen particularly in the pelvic region because this is the region that carries the biggest load with gravity present. A study demonstrated that in healthy mice osteoclasts appearance increased by 197% accompanied by a down-regulation of osteoblasts and growth factors that are known to help with the formation of new bone after only sixteen days of exposure to microgravity. Elevated blood calcium levels from the lost bone result in dangerous calcification of soft tissues and potential kidney stone formation. It is still unknown whether bone recovers completely. Unlike people with osteoporosis astronauts eventually regain their bone density. After a three to four month trip into space it takes about two to three years to regain lost bone density.

Radiation Threatens DNA And Immunity

Without the protection of Earth's atmosphere and magnetosphere astronauts are exposed to high levels of radiation. High levels of radiation damage lymphocytes cells heavily involved in maintaining the immune system. This damage contributes to the lowered immunity experienced by astronauts. Radiation has also recently been linked to a higher incidence of cataracts in astronauts. Outside the protection of low Earth orbit galactic cosmic rays present further challenges to human spaceflight as the health threat from cosmic rays significantly increases the chances of cancer over a decade or more of exposure. A NASA-supported study reported that radiation may harm the brain of astronauts and accelerate the onset of Alzheimer's disease. Solar flare events though rare can give a fatal radiation dose in minutes. It is thought that protective shielding and protective drugs may ultimately lower the risks to an acceptable level. Crew living on the International Space Station ISS are partially protected from the space environment by Earth's magnetic field as the magnetosphere deflects solar wind around the Earth and the ISS. Nevertheless solar flares are powerful enough to warp and penetrate the magnetic defenses 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. However beyond the limited protection of Earth's magnetosphere interplanetary human missions are much more vulnerable. Lawrence Townsend of the University of Tennessee and others have studied the most powerful solar flare ever recorded. Radiation doses astronauts would receive from a flare of this magnitude could cause acute radiation sickness and possibly even death. On the 31st of May 2013 NASA scientists reported that a possible human mission to Mars 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. 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. There is scientific concern that extended spaceflight might slow down the body's ability to protect itself against diseases. Radiation can penetrate living tissue and cause both short and long-term damage to the bone marrow stem cells which create the blood and immune systems. In particular it causes chromosomal aberrations in lymphocytes. As these cells are central to the immune system any damage weakens the immune system which means 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.

Twin Study And Soyuz Tragedy

On the 12th of April 2019 NASA reported medical results from the Astronaut Twin Study where one astronaut twin spent a year in space on the International Space Station while the other spent the year on Earth. This comparison demonstrated several long-lasting changes including those related to alterations in DNA and cognition after the twins were compared. The study provided critical data on how space travel affects human biology over extended periods. Another historical event illustrates the lethal nature of vacuum exposure. The only humans known to have died of exposure to vacuum in space are the three crew-members of the Soyuz 11 spacecraft. Vladislav Volkov Georgi Dobrovolski and Viktor Patsayev perished during preparations for re-entry from orbit on the 30th of June 1971. A pressure-equalisation valve in the spacecraft's descent module unexpectedly opened at an altitude causing rapid depressurization and the subsequent death of the entire crew. In December 1966 aerospace engineer and test subject Jim LeBlanc of NASA was participating in a test to see how well a pressurized space suit prototype would perform in vacuum conditions. To simulate the effects of space NASA constructed a massive vacuum chamber from which all air could be pumped. At some point during the test LeBlanc's pressurization hose became detached from the space suit. Even though this caused his suit pressure to drop in less than 10 seconds LeBlanc remained conscious for about 14 seconds before losing consciousness due to hypoxia. As he stumbled backwards he could feel the saliva on his tongue starting to bubble just before he went unconscious and that is the last thing he remembers. A colleague entered the chamber within 25 seconds and gave LeBlanc oxygen. The chamber was repressurized in one minute instead of the normal 30 minutes. LeBlanc recovered almost immediately with just an earache and no permanent damage. On the 2nd of 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.

Exercise And Countermeasures

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 and a stationary bicycle. Each astronaut spends at least two hours per day exercising on the equipment. Astronauts use bungee cords to strap themselves to the treadmill. Astronauts subject to long periods of weightlessness wear pants with elastic bands attached between waistband and cuffs to compress the leg bones and reduce osteopenia. Currently NASA is using advanced computational tools to understand how to best counteract the bone and muscle atrophy experienced by astronauts in microgravity environments for prolonged periods of time. The Human Research Program's Human Health Countermeasures Element chartered the Digital Astronaut Project to investigate targeted questions about exercise countermeasure regimes. NASA is focusing on integrating a model of the advanced Resistive Exercise Device ARED currently on board the International Space Station with OpenSim musculoskeletal models of humans exercising with the device. The goal of this work is to use inverse dynamics to estimate joint torques and muscle forces resulting from using the ARED and thus more accurately prescribe exercise regimens for the astronauts. These joint torques and muscle forces could be used in conjunction with more fundamental computational simulations of bone remodeling and muscle adaptation in order to more completely model the end effects of such countermeasures and determine whether a proposed exercise regime would be sufficient to sustain astronaut musculoskeletal health. Advances in research on exercise hormone supplements and medication may help maintain muscle and body mass. New techniques are being developed to help astronauts recover faster from bone loss. Research on diet exercise and medication may hold the potential to aid the process of growing new bone.

Mental Strain And Sleep Loss

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. There has been considerable evidence that psycho social stressors are among the most important impediments to optimal crew morale and performance. 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 an eighteen by twenty-foot cabin for a month Human nature won't stand it. NASA's interest in psychological stress caused by space travel initially studied when their crewed missions began was rekindled when astronauts joined cosmonauts on the Russian space station Mir. Common sources of stress in early American missions included maintaining high performance while under public scrutiny as well as isolation from peers and family. On the ISS the latter is still often a cause of stress such as when NASA Astronaut Daniel Tani's mother died in a car accident and when Michael Fincke was forced to miss the birth of his second child. 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 spacecraft. Even the habit of looking out of the window before retiring can send the wrong messages to the brain resulting in poor sleep patterns. These disturbances in circadian rhythm have profound effects on the neurobehavioural responses of the 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 took sleeping pills and still got two hours less sleep each night in space than they did on the ground. 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.

Mars And Future Unknowns

A round trip to Mars 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. 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. 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 the 29th of October 1998 John Glenn one of the original Mercury 7 returned to space at the age of 77. His space flight which lasted nine days provided NASA with important information about the effects of space flight on older people. Factors such as nutritional requirements and physical environments which have so far not been examined will become important. Overall there is little data on the manifold effects of living in space and this makes attempts toward mitigating the risks during a lengthy space habitation difficult. Testbeds 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.

Effect of spaceflight on the human body.

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