Space Hazards

4 min read

Space travel always seems cool in science fiction movies, and perhaps being an astronaut is something we all dream of.  Nevertheless, have you ever thought about what kinds of health challenges astronauts need to confront during their space travel? Space travel can be extremely taxing to our entire body. Let us explore three different challenges which our bodies face during space travel.

First, astronauts’ visual acuity can deteriorate during space travel.

In 2009, Dr. Michael R. Barratt spent six months aboard the International Space Station. Along the way, as a NASA astronaut and physician, Dr. Barret realized he began having trouble recognizing close objects. Dr. Robert B. Thirsk, a Canadian physician and a member of the same six-person team experienced the same issue. They gave each other an eye test and confirmed that they were becoming farsighted.

They also noticed a tendency for their optic nerves to swell, and the gradual formation of spots on their retinas.  Utilizing a high-resolution camera, they were able to take clearer pictures of their eyeballs, confirming their suspicions. Ultrasound images showed that their eyeballs had experienced increased pressure in some way. This condition is called visual impairment intracranial pressure syndrome, or VIIP, and the current leading hypothesis is that it is caused by the lack of gravity which leads pressure to build up in astronauts’ heads.

Maintaining the dynamic balance of body fluid volume, distribution and composition are necessary to ensure normal cell metabolism and maintain the physiological functions of various organs. On Earth, gravity pulls our body fluid towards our feet, but that is not the case in space. During space travel, extra fluid in the skull could be putting pressure on the back of the eyeballs, causing them to flatten, and pushing the retinas forward which distorts vision and makes people farsighted. Astronauts with hyperopia may have trouble operating their spacecraft. It also makes it harder for astronauts to detect potential dangers. Even some asteroids which may collide with the spaceship will become unobservable for astronauts with hyperopia. Blurred vision can increase the risk of mission failure and disaster in the space navigation.

The second is that astronauts could lose bone density and muscle mass travel during their time in space.

In space, the lack of gravity gives rise to weightlessness, and the absence of external force on the bone can cause bone tissue to atrophy and shrink, causing a decrease in bone density. Similarly, muscles can become weaker and lose their elasticity. The weightless environment breaks the balance between bone formation and bone resorption, so that bone formation is inhibited while bone resorption is more active, leading to osteoporosis. Even if astronauts are equipped with special equipment for muscle training, it may not necessarily help. Researchers from NASA have observed that in the state of weightlessness, bone density normally decreases by an average of 1-2% per month, whereas people on Earth lose only approximately 1% per year.

The loss of bone density and muscle mass caused by the weightless environment will lead astronauts to develop osteoporosis. Astronauts with low bone density are more susceptible to fractures and will lose muscle function due to decalcification. Meanwhile, the increase of calcium levels in the blood due to decalcification would cause an increased risk of renal stone formation. Changes in the urinary biochemistry of crew members during long-duration spaceflight demonstrated increases in the supersaturation of the stone-forming salts. In-flight hypercalciuria was evident in several individual crew members.

And finally, space radiation also threatens astronauts’ health. In addition to charged particles, there is a lot of high-energy short-wave radiation in space that is extremely harmful to living things, such as ultraviolet rays and X-rays from the sun. People on earth have the earth’s magnetic field which protects us from the solar wind, but in space, the astronauts are exposed to cosmic radiation. This strong radiation can penetrate living tissues and cause long-term damage to bone marrow stem cells, which can cause chromosomal abnormalities in lymphocytes – one of the many possible damages that radiation can inflict on the human body.

In conclusion, while space travel is mostly rosy in our imaginations, we should realize that astronauts will be afflicted by visual health problems, loss of bone density and muscle mass, and space radiation.

Written by Xinran Su
Illustrated by Jarrod Chua, @spaceytales


1. NASA HQ (29 May 2009). “Expedition 20 Crew Docks with Space Station”. NASA. Retrieved June 2009.

2. Mader TH, Gibson CR, Pass AF, et al. Optic disc edema, globe flattening, choroidal folds, and hyperopic shifts observed in astronauts after long-duration space flight. Ophthalmology. 2011;118(10):2058–2069. – PubMed

3. “Russian “Internal” Spacewalk Complete”. NASA. 10 June 2009. Retrieved 6 July 2009.

 4. ” Station Crew Completes Soyuz Move”. 3 July 2009. Retrieved 6 July 2009.



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