Biological and Psychological Effects of Human Space Flight

In 2010, Barack Obama passed a bill that will have important ramifications for American space flight in the near future. The bill was called the NASA Authorization Act and introduced several budgetary reforms to the organization, including the cancellation of the program Constellation, which would have expanded the technology necessary for human space exploration. Nonetheless, international investment in human space exploration persists, especially in agencies such as the Russian Roscosmos and European ESA. Considering this enduring global interest in manned missions, it is relevant to explore the effects of space travel on astronauts—both physiological and psychological. These discoveries, in turn, can help us develop adequate preparations for sending humans into space in the future.

One of the most prevalent physical ramifications of living in space is tissue loss; notably, bone decay, occurring at rates up to 1.5% loss per month in orbit1. Why does this occur? Existing literature about osteoporosis does not yet hold the full answer, but may be somewhat informative. Osteoporosis may be defined as the gradual bone loss that occurs when the rate of bone mineral resorption (the transfer of calcium from bone fluid to the blood) is greater than the rate of bone mineral deposition (the deposit of calcium compounds into the bone)2. Amongst the numerous risk factors for this condition, the primary factor related to space flight appears to be lack of exercise.  While mitigating benefits have been shown from regular exercise on a treadmill with resistance-inducing elastic straps, these benefits are just that—mitigating, and not yet fully protective. The same is applicable to muscle tissue, which tends to atrophy under the decreased demands of a zero-gravity environment. Take cardiac muscle as an example. Under normal conditions, gravitational pressure makes it necessary for the heart to pump faster to sustain blood flow. In absence of gravity, this pace is not sustained and decreases, with important consequences for readjustment upon return to Earth6.

The immune system is another biological structure affected by weightlessness. First, for a little background information. Monocytes, a type of white blood cell, play crucial functions in the immune system. Some of their roles include producing macrophages (infection killers), dendritic cells (immune system messengers), and cytokines (that respond to inflammation signals). Now, scientists often run experiments in microgravity conditions on Earth before attempting them in space, often inducing artificial microgravity by using magnetic fields9, 10. In one of these experiments, researchers observed that monocytes do not appear to fully mature into their subsequent forms (macrophages, dendritic cells, cytokines) in microgravity conditions8, 11, 12. Based on this discovery, scientists sent monocyte cultures into space and found similar results13,14,15. Adding to the problem, large infectious particles that would normally settle to the ground in a gravity-bound environment are free to float around the cabin in space16. All these factors combined result in an especially high prevalence of space infections and more minor conditions such as nasal congestion and puffiness in the face6.

Another important, if slightly less tangible, risk factor for astronauts is space radiation— that is to say, energy or matter that is not attenuated by the earth’s atmosphere. Said radiation can come from sources such as sunlight, subatomic matter moving through space, and matter-less particles (neutrinos)3. If enough radiation is present (i.e. during a solar storm), then it can be absorbed into the body of an astronaut, where it has adverse effects. Much like targeted radiation therapy in cancer treatment, general radiation results in the destruction of cells by damaging their DNA4. Radiation energy can displace electrons from atoms that had previously used them to form bonds with other atoms within a larger molecule5. According to NASA3, astronauts on the International Space Station experience what amounts to 8 chest X-rays of radiation per day.

There are also several neurologic consequences to space flight. In one notable experiment, the brains of rats sent to space aboard space shuttle Columbia were examined. Compared to the ground controls, space rats’ brains had significantly fewer connections between neurons18. This finding might help to explain the slower reaction times of astronauts in space in a series of tests19. Another rather dramatic effect of space travel is a disruption of the vestibular system, which is in charge of providing balance and spatial orientation. Under normal conditions, the gravity-sensitive otolith within the inner ear works in conjunction with sensory systems to provide feedback about a person’s position in the world. Now imagine you are floating in space. Your visual system detects an up and a down direction, but you feel no weight associated with your limbs to substantiate the perception.17 This perceptual contradiction results in space motion sickness, part of the constellation of symptoms under the general umbrella of space adaptation syndrome.

The psychological implications of space travel are just as significant as the physical ones. This is particularly true in long trips, where complications are more likely to arise. A mission to and from Mars, for example, would require crewmembers to cohabit in close quarters for approximately three years. Research has been conducted on somewhat analogous situations, such as extended Antarctic expeditions. Here, typical behavioral patterns have been uncovered—notably, a half-point surge of depression in travelers who realize how much of the journey there is still left22. In other relevant research, scientists investigated the properties of successful leaders and found that in the long run, leaders who focused on how people felt were more successful than task-oriented leaders- a principle that would be useful when applied to managing crewmember interactions on long duration space flights. Last but not least, studies have been conducted on the importance of astronaut-ground crew interactions, and have been applied to subsequent training of both astronauts in orbit and ground personnel23. In the end, it takes a specific kind of person to make a good astronaut—in particular, one with an elevated capacity to regulate stress, temporarily displace emotions, and filter out preoccupying thoughts20. In addition, astronauts must be highly resilient to environmental sources of psychological distress including isolation, interrupted sleep cycles, the hyperarousal caused by excitement, intense work schedules, and the absence of day and night in space21.

With all these possible outcomes in mind, is it still worth it to send astronauts into space? Given the redeeming scientific boons of space exploration and progress made in solving problems related to it, the answer is, increasingly, yes. Seeing as efforts to minimize the impact of zero gravity (i.e. exercise treadmills with heavy straps to exert tension on muscles and bones) have proven somewhat inadequate, the ideal answer might be to induce artificial gravity. One suggestion for doing this is to rotate the vehicle itself. Unfortunately, approaches such as this one are currently expensive and would require much attention to various engineering and safety issues.1. Until a more feasible solution is found, training and medical screenings remain simple but important ways to predict and minimize harmful side effects. Another simple preventative measure is to forecast environmental conditions before launch. While the radiation levels astronauts have been exposed to in space are high, they cannot compare to the deadly doses emitted by a solar flare. Scientists have now refined their detection techniques enough to predict solar flare onset two to three days in advance, by focusing on magnetic fields below the surface of the sun25. Besides this, research on effective measures to counteract Space Motion Sickness is being conducted and includes anti-motion sickness drugs, autogenic feedback training, and mechanical restraints (eg: neck braces) to prevent excessive activity. International research continues to progress, and will increasingly allow us to extract important functional practices to improve astronaut living conditions during space travel, which ultimately represents a crucial way to learn about our universe.


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  15. Czarnik, Tamarack. “Medical Emergencies in Space.” Mars Society
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  19. Mason, Stephen. “How do Astronauts Remain Calm During Blast Off.” Psychology Today
  20. Sharke, Stephanie. “Psychological and Physiological Barriers of a Mission to Mars.”
  21. “How Astronauts Get Along.” NASA.
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  24. “NOAA Scientist Finds Clue to Predicting Solar Flares.” National Oceanic and Atmospheric Administration.
  25. Space Shuttle Columbia Launching.
  26. Astronaut EVA.

Isabelle is a fourth-year student at the University of Chicago majoring in Biology and Psychology. Follow The Triple Helix Online on Twitter and join us on Facebook.