The centrifuge has a great role in the aerospace industry, especially for pilots and astronauts. During the astronaut training process, it is necessary to adapt to the reflection of hypergravity acceleration, and gravity acceleration depends on the completion of the centrifuge
1. Overweight model
Gravity (g) is a gravitational force between two objects in the universe, and its value can range from zero to infinity. For example, the gravity on the moon is 0.17g, on Mars is 0.3g, the earth is 1g, the centrifuge can produce a gravity greater than 1g. Using ultra-high-speed centrifuge can produce 103105g of force. When the spacecraft enters Earth orbit at a height of 200 miles (321.8 kilometers), its gravity is equivalent to 95% of the surface of the earth, but due to the centripetal acceleration of the spacecraft, it cancels out the gravity of the earth, so that the objects on the spacecraft moving around the earth are in 10-2 ～ 10-5 g of gravity. During the launch-flight-return process, the spacecraft experienced a gravitational change of overweight-microgravity-overweight. In order to launch the spacecraft into different orbits, the method of multi-stage launch vehicles is generally adopted. Each stage of the launch vehicle will generate a certain acceleration to form an overweight with different g values. The early rockets were 7-8g overweight, the new rockets were less than 5g, and the peak value of the space shuttle during launch was controlled at about 3g. The spacecraft also encountered overweight during the return process. The peak value of the early overweight was controlled above 10g, the peak value of the new spacecraft was reduced to 5-7g, and the overweight value of the space shuttle was controlled within 2g.
Animals, plants and people living in the spacecraft are also subject to overweight and weightlessness during the spaceflight. The creatures on the earth have evolved in a 1g environment, and they have formed an organizational structure adapted to the 1g gravity environment. When plants and animals enter another gravity environment, they must readjust to the new gravity environment. The relationship between their response to gravity and gravity may be a linear or mathematical function. The tissue structure adapted to 1g in an organism will become unbalanced or degraded in an overweight or low gravity environment to adapt to the new gravity environment. The astronauts' cardiovascular dysfunction, muscle atrophy, and osteoporosis in flight are a good example. When the organism adapts to the new environment and returns to the environment of 1g on the ground, there will be a non-adaptation reaction, which needs to go through a process of re-adaptation. Therefore, it is necessary for the development of the aerospace industry to study the impact of changes in gravity on organisms, especially the effects of microgravity. At the same time, this research also has important theoretical significance for understanding the role of gravity in the evolution of organisms.
Research on gravity beyond 1g is relatively easy, and it can be achieved on the earth by using different types of centrifuges. It is impossible to conduct a long-term, less than 1g gravity study on the earth. You can only leave the earth and go to the space laboratory or to those planets with lower gravity than the earth (such as the moon and Mars). But conducting multiple biological studies in space is unrealistic. The main reasons are:
(1) The cost of conducting biological research in space is very high, and there are many tasks for each flight. It is impossible to conduct special biological and medical research.
(2) In addition to microgravity factors in the aerospace process, overweight, vibration, noise, radiation, gas environment in the cabin, and harmful substances all have an impact on the measured object and affect the analysis of the experimental results.
(3) Individuals of organisms, especially humans, have large differences, and many repeated experiments are required to find their regularity. At the same time, there are many projects that need to be studied. It is impossible to conduct so much research in aerospace.
(4) Each research requires the participation of experts in this academic field and various specialized scientific instruments, which are not available in aerospace. Therefore, it is necessary to establish a model to simulate the change of gravity on the ground.
The model established on the ground to simulate the overweight and microgravity in the aerospace process helps to achieve the following purposes:
(1) Understand which systems in the organism sense gravity,
Determine their thresholds, mechanisms to adapt to changes in gravity, ability to adapt, and time to adapt.
(2) Predict how the body that has been adapted to overweight and low gravity will adapt to the 1g environment.
(3) Propose preventive measures to mitigate potential problems that may occur when re-adapting to 1g environment.
A centrifuge can be used on the earth to achieve overweight. The centrifugal acceleration of the centrifuge generates a centrifugal force parallel to the ground. It and gravity form the two sides of a right triangle, and the combined force is the gravity generated by the centrifuge rotation. Therefore, a 1.5g centripetal acceleration force can produce a 1.8g resultant force, and a 4g centripetal acceleration force can produce a 4.1g resultant force. The centrifuge is composed of a power system, a central rotating shaft and a rigid rotating arm (Figure 1). The arm length of the centrifuge varies from 1 to 8 meters. The arm length of the centrifuge is related to the rotation speed. The longer the arm, the lower the rotation speed; the shorter the arm, the higher the g value. However, if the subject in the short arm is very tall, the centrifugal force on different parts of his body will be different, and the factors affecting the subject will be complicated. Therefore, short-arm centrifuges are generally used for small plants and animals. According to different experimental purposes, centrifuges with different sizes and different forms can be constructed. Some centrifuges can change the position of the cabin on the connecting arm to generate different sizes of gravity according to different test requirements, while other centrifuge cabins can only be fixed at the end of the mechanical arm to provide a specific size of gravity.
The cabin of the centrifuge can generally rotate freely on the arm to keep the gravity component in the direction of the earth's gravity. The cabin of some centrifuges can change its own direction to suit special experimental requirements. A NASA research center has a set of centrifuges, which includes a special centrifuge for vestibular research (VRF, with two 0.8-meter arms that can rotate on 3 axes), and a human centrifuge (arm length 7.6 meters) And rotating house (arm length 8.125 meters). The VRF centrifuge is used to study the effects of some complex factors on small animals such as cats, monkeys, birds, and fish. Experiments can be conducted on a VRF centrifuge for hours to days. Other animal centrifuges are mainly used to study the adaptive response of rodents in overweight environments and to provide overweight conditions for some space experiments.
The human centrifuge is mainly used to study the physiological response and sensation changes of people in the overweight state after returning to space and lying in bed. It can also be used for the selection and training of astronauts' overweight endurance. The test time of the human centrifuge usually does not exceed one hour. The ability of the tested organism to resist overweight is inversely proportional to its own mass. Plants, insects and rodents can withstand gravity far more than humans. For example, small, young plants can easily persist for 10 minutes in an environment of 30-40g without obvious structural changes, and even the effect of hundreds of g will not cause obvious damage to the structure of the plant; rats only Can bear the gravity of 15g for 10 minutes, if the gravity reaches 20g, it will all die; people can bear the head
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