According to the measurement, astronauts lose 1% ~ 2% of calcium in one day, especially in bones. Therefore, the bones of astronauts who fly back will become looser, more brittle and prone to fracture. The calcium content in astronauts' urine is three times that of the ground, indicating that calcium is mainly lost through urination.
After a flight, astronauts will lose 4 ~ 6 kilograms. But returning to the ground can increase 2 kilograms a day, which is related to the easy dehydration of the human body in space. In space flight, dehydration is inevitable because of the disorder of body fluids and the redistribution of blood. The pilot's body volume of the lunar module of Apollo spacecraft in the United States is 2.5 liters less than that of the ground, while the pilot's body of the command module is even 6.9 liters less.
When the spacecraft orbits the earth once, the centrifugal force of the spacecraft motion is equal to the gravity of the earth on the spacecraft. Because these two forces are in opposite directions, people and objects on the spacecraft are in weightlessness. In weightlessness, some unimaginable wonderful and interesting phenomena will appear, which will have an important impact on people's life and health.
In the process of evolution, human beings have lived under constant gravity for a long time, forming a balance of internal environment. The main components of the human body are composed of soft tissues, bones and body fluids, and gravity has different effects on these components, forming a certain proportion between these basic components in evolution. The sturdiness of bone structure, its function, the main activities of muscles and the distribution characteristics of body fluids ensure the resistance to gravity and enable the human body to survive and grow.
Before human beings went into space, it was predicted that weightlessness might destroy the balance of human internal environment and make irreversible changes in human physiological functions, and even asserted that whoever wanted to get rid of gravity would die of heart failure. The practice of human life in space proves that people's physiological functions will change under weightlessness, but it is not as serious as the pessimists predicted. Under weightlessness, the physiological function of human body changes, mainly because of the redistribution of blood and body fluids, and a large amount of blood and body fluids are concentrated in the head and upper body. About 2 kilograms of blood and body fluids accumulate in the head and chest, causing vasodilation of the head and chest, edema of the face and upper limbs, and atrophy of the lower limbs; Chest tightness is aggravated and the heart is enlarged; Red blood cells in blood decreased by about 10%, cardiac output decreased by 30%, and systemic blood volume decreased by 20%. A large amount of water loss in the body leads to a decrease in plasma concentration and blood volume. Astronauts have just stepped off the ground from the spaceship, and they can't even walk upright for a while. They need someone to help them for a while before they can move, which also shows that their physical strength is quite high.
People who are used to the life of the earth's gravity will feel novelty once they enter the weightless environment. The weight of the human body has disappeared, and it is really as light as a swallow, and the palm can dance. Can fly freely in the engine room; Or you can stay in the air. In the case of weightlessness in the air, it is equally comfortable to sleep standing, sitting and lying down, but you must fix yourself on the seat with a belt or tie yourself up with a fixed sleeping bag to prevent you from drifting away or bumping around. Because there is no day and night in the spaceship we are used to, we can only carry on our daily life by the hour.
In the case of weightlessness, astronauts will feel that their head perception and body perception are not harmonious. When they close their eyes, they can't judge the relative position between the objects around them and their bodies, and sometimes they feel that they are looking at the stars and hallucinating.
In weightlessness, people's posture reflex fails, they can't sit still, so they should be very careful when walking. They should wear special shoes with claws on the soles, and when they want to stand, they should insert their claws into the lattice bulkhead to stabilize their bodies. If you go outside the cabin, you must control your movements by operating a set of jets worn on your body.
Astronauts not only have to lead a strange life in space, but also bear the test of strong "overload" when the spacecraft is launched from the ground. In the early acceleration stage of spacecraft launch, astronauts had to bear 5 ~ 5g of "overload", which made people feel that their weight had increased by five or six times. If they sit in a sitting position, human blood will flow to the lower limbs, leading to the death of brain cells due to anemia and hypoxia, so the astronauts must lie down. The "overload" of modern spacecraft such as the space shuttle is only 3G, which ordinary people can bear, which creates conditions for more popular space travel.
At present, the research of human physiology in space is being carried out step by step, and there are many experiments to be carried out, including the balance of inorganic salts in space, the changes of biochemical reactions of body fluids, the changes of trace elements in the body, the changes of human immunity, cardiovascular concentration and strain performance, the changes of red blood cell life, the changes of human metabolic rate, vestibular function and so on. It can be predicted that these studies will reveal more questions about how people change in space.