The maximum duration that a normal human can live in space is 437 days, according to a study conducted by Valeri Polyakov nearly 20 years ago during his second space mission. In his first mission, it lasted only 240 days. Another astronaut, Sergei Krikalev, has a total space experience of 803 days over six space missions.
As we know, the space environment is harsh for human beings. The evolution of the human body is designed to withstand the gravitational forces of Earth rather than adapt to life in space.
Our muscles constantly need to be in motion to adapt to the gravity on Earth, but in the weightless space environment, it is different. Without gravity, muscles do not move, and muscle groups tend to shrink. The most affected are the heart, neck muscles, and the muscles in the legs, which also experience some degree of shrinkage. Additionally, the absence of weight-bearing loads on the body leads to bone loss and decreased bone density, making our bones more susceptible to fractures.
There is ample evidence showing that prolonged exposure to space leads to disruptions in the human immune system. The space environment provides favorable conditions for the proliferation of pathogens, and if the immune system is compromised, it can result in hypersensitivity reactions to the surrounding environment.
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In addition to the challenges posed by gravity, radiation poses a potential threat. In some studies, scientists have identified a distance of 27,000 miles as the Earth’s magnetic field boundary that shields us from radiation. Beyond this limit, space travelers are exposed to various types of radiation, and it is evident that even when astronauts close their eyes, they can still “see” light as these radiation rays hit their optic nerves. Direct exposure to radiation can damage human cells and cause mutations, leading to cancer or genetic effects. Some organs in the body are particularly sensitive to radiation and can weaken their functions, such as the immune system, the bone marrow system, and especially the eyes, posing a risk of cataracts.
A paradox arises as scientists strive to find ways to shield astronauts from harmful radiation. There is a phenomenon called secondary radiation, which negates their efforts as shielding materials can produce gamma rays and high-energy neutron particles upon interaction with radiation, posing direct risks to astronauts.
As a result, NASA strictly monitors radiation exposure, closely monitoring the exposure of each crew member and maintaining stringent protocols. When the radiation levels reach the permissible threshold, astronauts may be temporarily prohibited from further space travel.