Impacts+of+Space+Travel+on+Human+Body

=**Introduction **=

Space travel is a dream that has become true in recent decades. Not only is it a dream anymore, but a toc source of aspirations and ambitions for human development such as mining meteors, harnessing sun’s energy and exploring new planets. Companies like SpaceX have proposed plans to allow public to travel to the moon for tourism in as soon as 2018. As much excitement about this idea, it is important to understand the inevitable effects as well as the risks that lay ahead of space travel to human body and inform the public about these impacts priorly

=**Effects on Human Body **=

**Nausea **
One of the first things that astronauts have to deal with is the nausea followed by puking [1]. Due to the lack of gravity, sensitive inner ear destabilizes the balance, co-ordination, and [|spatial orientation] of the body. It also affects the ability to track objects at motion [1]. This costs the astronaut his piloting skills. For instance, Apollo-9 astronaut Rusty Schweickart was not able to perform some of his tasks due to nausea and Anousheh Ansari, a space tourist, mentioned the same problems of nausea, puking and instability [1]. While tourists need to enjoy the scenery of space, they will face the same problem due to the lack of gravity.

**Loss of Consciousness **
Right after launch, due to the high acceleration of spacecraft that could reach up to 4g, body feels four times as heavy and pulled-back to the seat with difficulty in moving body parts. When the body is parallel to the direction of acceleration, gravitational forces pull blood down to the feet. This blood is needed in the brain to stay conscious, however, and this causes passing out of the passenger [1]. Fortunately, Modern spacecraft align the body perpendicular to the acceleration so that forces are felt only through the chest. [1]

**Sight Problems **
Two thirds of International Space Station astronauts reported having problems with their sight [3]. A follow-up study by the National Center for Biotechnology Information acknowledged that astronauts’ eyeballs were a bit flattened after six months in orbit [6]. NASA believes that happens due to the lack of gravity which makes the blood and all body fluids redistribute more evenly throughout the body including the [|intracranial fluid], the fluidic that’s behind the eyeball, which increases pressure on the back of the eye causing the flattening [2][6]. This impairment is known as [|visual impairment intercranial pressure syndrome (VIIP)]. A good metaphor would be spraying water on the back of a balloon. When that happens, focal length of the eye will change, and as a result, the visual acuity will change.

**Sleep Deprivation **
Sleep deprivation is one of the most commonly encountered issues. In an orbit, a new dawn every 90 minutes makes it impossible for astronauts to adapt. Although there are artificial night times, astronauts still struggle with them due to their biological sleeping habits [1].In addition, astronauts have to adapt work shifts and sleep strapped to a wall in a sleeping bag [1]. International Space Station (ISS) has tried to counter these issues by equipping astronauts with individual compartments with LED light system which can darken these compartments and minimize other lights to simulate night [1].

**Muscle Loss **
Muscles and bones stay active by fighting gravity on earth and many body systems depend on gravity to stay functional. As soon as gravity goes, body begins to decay [1][2][3]. For example, heart and body muscles deteriorate leaving the body unable to walk. Not only that but also they leave the astronaut prone to severe injuries in muscles upon return to earth, when gravitational pressure is back. The lack of gravity makes [|cardiovascular system] less effective distributing blood all around body. Instead, it pumps blood up to the head and chest instead rising the risks of high blood pressure [3]. Astronauts work out 2 hours a day which is the amount needed to maintain functionality of bones, muscles, and cardiovascular system as well as psychological help [2]. These exercises act as artificial gravity to compensate gravitational work [9]. Although many pre-flight programs for astronauts have been made by the ISS that include weightlifting and cardiovascular training, after months in orbit, astronauts still struggle to walk when back on earth [1]. It was shown that despite the training in space stations, a huge decline in muscle fiber mass, force, and power occurs due to weightlessness [8].

**Bone Loss **
<span style="font-family: Arial,sans-serif; font-size: 12pt;">Lack of gravity, also, contributes a great deal in dissolving bones [1][2][9][11]. 1-2% loss in important bones of astronaut were reported during a month of space travel [1]. Loss of Calcium is ten times faster than normal aging process of bone on earth which poses a great threat of permanent fracture upon return to earth [9]. Also, loss of bone mineral content, especially Calcium, increases the levels of those minerals in the urine which will pose an increased risk of [|kidney stones] [9]. It was demonstrated that heavy exercise and good nutritional status can reduce loss of bone minerals [11]. The extent of this reduction, however, is uncertain and the effectiveness/optimization of exercises is highly debated [11].

=**<span style="font-family: Arial,sans-serif; font-size: 14pt;">Hazards on Human Body **=

===**<span style="font-family: Arial,sans-serif; font-size: 12pt;">Radiation **=== <span style="font-family: Arial,sans-serif; font-size: 12pt;">Radiation is another risk that astronauts encounter. Bright flashes of light are reported by astronauts which happen due to [|cosmic rays]. When in deep space, chances are higher to get lethal doses of cosmic rays making long duration missions increasingly difficult [1]. Radiation in space is between 100 and 1000 times higher than radiation on earth [3]. According to Medical News Today, average amount of radiation exposure on earth is about 0.6 to 2.4 millisieverts (mSv) while in space, where there is no protecting ozone layer, ultraviolet radiation is pouring down with amounts as high as 200 mSv and reaches 600 mSv when travelling between planets, mutating the DNA of any lifeforms in space, and leaving them to deal with high likelihood of cancerous diseases [2][3]. The situation gets much worse when leaving earth’s protective magnetic field which shields off cosmic rays composed of high energy subatomic particles from the sun and beyond that can quickly devastate body tissues [4]. Also, chances of negatively affecting the immune system is equal or even higher than chances of getting mutations [4]. While some materials such as aluminum and polyethylene plastics can slow down radiation and therefore could potentially be used to shield spacecraft, slowing down these particles might still be dangerous as they may collide with other particles and regenerate radiation. This topic is a major concern in space travel and landing on Mars depends pretty much on solving this issue [2].

**<span style="font-family: Arial,sans-serif; font-size: 12pt;">Disease **
<span style="font-family: Arial,sans-serif; font-size: 12pt;">Research by NASA has shown that immune system is weaker in space making the passengers more susceptible to diseases. An experiment on a fruit fly has shown that the fly’s white blood cells were less effective handling bacteria inside the body in outer space than in earth. Gravity is likely the reason for this [1]. Furthermore, study by Japanese Science and Technology Information Aggregator shows that bacteria inside humans, like [|Pseudomonas aeruginosa] and [|Staphylococcus aureus], seem to endure the conditions in space station [7] and turn virulent in human body [2] ,and as mentioned before, immune system does not function as good in space due to gravity thus leaving the astronaut defenseless to diseases [5][10]. Due to the unavailability of extensive care or hospital in a space station, any infection could be lethal and disastrous to the whole crew. Taking antibiotics is too much of a risk to handle as they eliminate beneficial bacteria which would further dwindle the immune system [2]. This has been worrying NASA’s Human Research Program and they are conducting extensive research on the immune changes in space.

=**<span style="font-family: Arial,sans-serif; font-size: 14pt;">Conclusion **=

<span style="font-family: Arial,sans-serif; font-size: 12pt;">In summary, space exploration and investment is important but so is the safety and health of space explorers. Studies have show <span style="font-family: Arial,sans-serif; font-size: 12pt;">n that there lies many biological risks accompanied with space travel that vary by stage of trip, longevity of trip, and distance from earth. Space agencies like NASA are constantly developing ways to mitigate these risks. Artificial gravity and night-simulating LED systems in space stations could be developed as solutions to bones and muscle decaying, and unstable sleeping habits for astronauts, respectively. Other research is underway to find solutions to the high radioactivity in outer-space and bacterial diseases among crew. Even then, there are other concerns related to the psychological state of astronauts and possibility of depression due to the repetitive tasks for long times in a relatively small space with few other mates.

**<span style="font-family: Arial,sans-serif; font-size: 14pt;">References **

<span style="font-family: Arial,sans-serif; font-size: 12pt;">[1]R. Hollingham, “The Effects of Space Travel on Human Body,” BBC//.// May 6, 2014. <span style="font-family: Arial,sans-serif; font-size: 12pt;">[|**http://www.bbc.com/future/story/20140506-space-trips-bad-for-your-health**] <span style="font-family: Arial,sans-serif; font-size: 12pt;">[2]M. Stone, “The Biggest Health Risks to Humans in Space,” Gizmodo. Oct 8, 2015. <span style="font-family: Arial,sans-serif; font-size: 12pt;">[|**http://gizmodo.com/here-are-the-biggest-health-risks-to-humans-in-space-1732733392**] <span style="font-family: Arial,sans-serif; font-size: 12pt;">[3]K. Houser, J. Javelosa, “Research Shows How Space Travel Affects Humans.” Futurism. Jan 16, 2017. <span style="font-family: Arial,sans-serif; font-size: 12pt;">[|**https://futurism.com/research-shows-how-space-travel-affects-humans/**] <span style="font-family: Arial,sans-serif; font-size: 12pt;">[4]R. B. Setlow, “The Hazards of Space Travel,” EMBO Reports, vol. 4, no. 11, pp. 1013–1016, Nov. 2003. <span style="font-family: Arial,sans-serif; font-size: 12pt;">[|**https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1326386/**] <span style="font-family: Arial,sans-serif; font-size: 12pt;">[5]B. E. Crucian et al., “Plasma Cytokine Concentrations Indicate That In Vivo Hormonal Regulation of Immunity Is Altered During Long-Duration Spaceflight,” Journal of Interferon & Cytokine Research, vol. 34, no. 10, pp. 778–786, Oct. 2014. <span style="font-family: Arial,sans-serif; font-size: 12pt;">[6]T. H. Mader et al., “Optic Disc Edema, Globe Flattening, Choroidal Folds, and Hyperopic Shifts Observed in Astronauts after Long-duration Space Flight,” Ophthalmology, vol. 118, no. 10, pp. 2058–2069. <span style="font-family: Arial,sans-serif; font-size: 12pt;">[7]K. Venkateswaran, M. T. La Duc, and G. Horneck, “Microbial Existence in Controlled Habitats and Their Resistance to Space Conditions,” Microbes and Environments, vol. advpub, 2014. <span style="font-family: Arial,sans-serif; font-size: 12pt;">[8]R. H. Fitts, P. A. Colloton, S. W. Trappe, D. L. Costill, J. L. W. Bain, and D. A. Riley, “Effects of Prolonged Space Flight on Human Skeletal Muscle Enzyme and Substrate Profiles,” J Appl Physiol, vol. 115, no. 5, p. 667, Sep. 2013. <span style="font-family: Arial,sans-serif; font-size: 12pt;">[9]L. David, “Artificial Gravity and Space Travel,” BioScience, vol. 42, no. 3, pp. 155–159, 1992. <span style="font-family: Arial,sans-serif; font-size: 12pt;">[10]A. T. Borchers, C. L. Keen, and M. E. Gershwin, “Microgravity and Immune Responsiveness,” Nutrition, vol. 18, no. 10, pp. 889–898, Oct. 2002. <span style="font-family: Arial,sans-serif; font-size: 12pt;">[11]S. M. Smith et al., “Fifty Years of Human Space Travel: Implications for Bone and Calcium Research,” Annu. Rev. Nutr., vol. 34, no. 1, pp. 377–400, Jul. 2014.