How dangerous is space to humans?

 Space is an extremely unfriendly environment for humans: there is no air, and it is full of deadly particles in the form of high-energy photons and high-energy atomic nuclei. Weightlessness will also affect all parts of your body, and even the protein in your body can't distinguish the up and down direction.

Books and magazine articles about space travel often liken this kind of adventure to traveling through an unpredictable ocean to a magical and beautiful new world. Human ancestors used primitive tools to handcraft a canoe across the Pacific Ocean in Vietnam. When they set off, they did not expect to return safely. They spent days, weeks, and even months on open water, exposed to harsh environments with only a small amount of food and water. Many people died on the way, but a few people arrived at their destination and started a new life.

There is no doubt that the early migration of humans tens of thousands of years ago is full of dangers, but sea water will not damage your DNA; sea fog will not damage your brain cells; no matter how turbulent the waves are, it will not cause fluid accumulation in your eyes. Will not cause permanent retinal damage. When you finally reach the land, you can walk. You won’t need doctors and engineers to lift you off the boat because your legs are too weak. Moreover, when you reach your destination, you will most likely find food and water immediately.

In short, although humans cannot survive in the sea, we can use driftwood to cross the sea. However, space is completely different from the ocean. In the past hundreds or even thousands of years, the challenges faced by mankind in every journey on Earth, no matter how arduous, pale in comparison with space travel beyond the moon. From an engineering point of view, space travel is technically feasible. After all, we sent humans to the moon 50 years ago. We have also launched numerous probes into the solar system, and made soft landings on Venus, Mars, Titan, Comet 67P/Churyumov-Gerasimenko and some asteroids. However, many doctors still believe that sending humans beyond the moon is very dangerous and is tantamount to suicide.

　　 How dangerous is space?

　　 The radiation exposure level of astronauts traveling on Mars far exceeds the radiation level of the earth’s workplace. When considering sending astronauts to Mars, the National Aeronautics and Space Administration (NASA) needs to obtain a special exemption based on the "As Low As Reasonably Achievable" (ALARA) principle. This exemption requires NASA to carefully assess the health risks of astronauts before launch.

However, radiation exposure is only one of the dangers. NASA's "Human Research Roadmap" identified 34 known health risks and 233 "gap" related to risk perception. For example, there are four known health risks related to radiation: radiation poisoning caused by solar flares; brain damage; cardiovascular damage; and general cancer. As for the cognitive gap, it is mainly about heredity, fertility and the influence of space radiation on infertility. Therefore, space travelers are likely to encounter more health risks beyond our knowledge. The following are 34 known risks of space travel (basic mechanical failures such as rocket explosions are not included):

　　1. Unpredictable drug effects related to clinical practice;

　　2, the risk of intervertebral disc injury after exposure to gravity again;

　　3. The risk of acute (in-flight) and late central nervous system reactions caused by radiation exposure;

　　4. The risk of acute radiation syndrome caused by solar particle events;

　　5. Bad cognitive or behavioral reactions and the risk of mental disorders;

　　 6. Exposure to cosmic dust may adversely affect health and work performance;

　　7. The risk of adverse health effects due to the interaction between the host and microorganisms;

　　 8. The risk of adverse health events caused by changes in immune response;

　　9. The risk of poor health outcomes and decreased work performance due to in-flight medical conditions;

　　 10. The risk of unreasonable residential design;

　　11. The risk of fracture due to bone changes caused by space flight;

　　12. The risk of heart rhythm problems;

　　 13. Radiation exposure and secondary space flight stressors lead to the risk of cardiovascular disease and other degenerative tissue problems;

　　14, the risk of decompression sickness;

　　 15. Space flight leads to the risk of early-onset osteoporosis;

　　 16. Due to changes in the vestibular/sensory motor abilities related to space flight, it is impossible to fully control the spacecraft/related systems and there is a risk of performance degradation;

　　17. The risk of decreased work performance due to impairment of muscle mass, strength and endurance;

　　 18. The risk of insufficient human and automation/robot integrated design;

　　19. The risk of insufficient human-computer interaction;

　　20. The risk of insufficient task, process and task design;

　　 21. The risk of undernutrition;

　　22. The risk of ineffective or toxic drugs due to long-term storage;

　　23. The risk of injury and performance degradation caused by EVA operations;

　　24. Risk of damage to dynamic loads;

　　 25. There is a risk of erectile intolerance when exposed to gravity again;

　　26. Due to insufficient teamwork, coordination, communication, and psychosocial adaptation, the risk of decreased work performance and behavioral health;

　　27. Due to insufficient food system, the risk of physical function decline and illness;

　　28. The risk of decreased work performance and poor health outcomes due to lack of sleep, circadian rhythm disorders and overloaded work;

　　29. The risk of work errors due to insufficient training;

　　30. The risk of cancer caused by radiation;

　　31. The risk of astronaut health and work performance decline due to low pressure and hypoxia;

　　 32. The risk of decreased physical function due to decreased aerobic capacity;

　　 33, the risk of kidney stone formation;

　　34. The risk of neuro-visual syndrome associated with space flight.

　　 Among these 34 risks, three are potential “terminators” for astronauts: radiation, gravity (or lack of gravity), and conditions that require surgery or complex medical procedures.

　　The importance of gravity

　　 Let us explore the problem of gravity.

　　 Some science fiction writers in the mid-twentieth century speculated that zero gravity allowed people to regenerate: blood would flow more easily; arthritis would be a thing of the past; back pain would be cured forever; even aging itself would slow down. However, the information we got from the early space program shows that such a beautiful scene is unreal.

There are three risks that are potential terminator for astronauts: radiation, gravity (or lack of gravity), and situations that require surgery or complicated medical procedures. There are three risks that are potential terminator for astronauts: radiation, gravity (https://www.brandnews.cc) ) And situations that require surgery or complex medical procedures

　　 When astronauts return to Earth from a state of weightlessness for several days, they will feel very weak, but they will soon recover, so many people think that weightlessness may not be so bad. Let’s take a look at those who have spent more time in space. When the Russian astronauts who had lived on the Mir space station for several months returned to Earth, they seemed to have some serious, longer-lasting health problems. Some astronauts regarded as heroes rarely show up in public after returning to Earth. It is the mission of the International Space Station that has conveyed to us such a message: Long-term weightlessness will harm human health in many ways. NASA has done a lot of work in this area.

　　 Before proceeding, let us define some terms. The first is "Zero Gravity." Although it looks like this, it may be a misnomer in the context of low Earth orbit. Astronauts on the International Space Station do not live in an environment without gravity. On the contrary, they are in free fall, always on the horizon and never on the earth. The International Space Station and other satellites float in space not because they escape the gravity of the Earth, but because of their amazing horizontal speed. The International Space Station is operating at an average speed of 2,7743.8 kilometers per hour. If it stops completely in some way, it will fall directly to the earth. In fact, the gravity of the earth keeps the satellites in orbit in full balance. If there is no gravity (for example, the earth disappears suddenly and magically), the satellites will be launched in a straight line at the lateral speed set during launch. Therefore, when describing the lack of gravity on the International Space Station, the more accurate terms should be "microgravity" and "weightlessness."