Why does the space station only "fly" 400 kilometers high (new knowledge)

　　Space station, also known as space station or space station, is a manned spacecraft that operates for a long time in low-Earth orbit and can be visited by multiple astronauts for long-term work and life.

Generally speaking, most space stations operate in orbits at an altitude of about 400 kilometers. For example, my country's Tiangong-1 and Tiangong-2 space laboratories, the International Space Station that is still in orbit, and the Chinese space station that we have begun to build.

　　Why does the space station only "fly" 400 kilometers high?

　　Everyone knows that space launches are very expensive.

The space station needs to consume more energy to fly to a higher orbit, which is a big test for the carrying capacity of the launch vehicle.

If you want to carry tons of equipment to a higher height, it is not necessary, and the cost is too high.

　　In fact, the atmosphere gradually becomes thinner as the altitude increases, and there is no clear and clear boundary between space and the Earth’s atmosphere.

The International Aviation Federation defines a height of 100 kilometers as the boundary between the atmosphere and space, that is, the "Carmen Line". The part outside the Carmen Line is called space.

The general space experiment requires a close-to-vacuum environment, the advantages of telescope observation without cloud cover, and the nearly gravity-free experimental conditions, etc., all of which can be met at an altitude of 400 kilometers.

　　This altitude setting also considers the safety of the astronauts and the space station itself.

　　There is a space area called the "Van Allen Radiation Belt" around the earth, which is roughly divided into an altitude range of 1500-5000 kilometers and 13000-20000 kilometers, and will expand upward and downward when space weather is disturbed.

There are charged particles with very high energy and very high density in this area, which is very harmful to the aircraft flying in it.

It is worth noting that because the geomagnetic field itself is not symmetrical, the shape of the geomagnetic field above the South Atlantic causes the radiation zone to be relatively low. When there is disturbance, it may only be about 1,000 kilometers high. The space station is easy to enter when it is flying high. Radiation belt, damaged by charged particles.

　　Considering launch costs, observation requirements, as well as factors such as the health of the astronauts and the safety of aircraft and equipment, the scientists set the altitude of the space station to be near 400 kilometers.

Wang Zheng

Wang Zheng