The principle of space elevator is not complicated, why hasn't it been built yet?

Why do you want to add counterweight? Because we want to lower the height of the elevator. Going back to the rope problem just now, according to the calculation, in order to achieve the balance between gravity and centrifugal force, this rope must extend straight up to 654.38+ 10,000 kilometers, and it is not necessary for our elevator to be built as high as 654.38+ 10,000 kilometers. Therefore, a large iron block should be added to the upper end of the rope (elevator). According to the centrifugal force formula, after the upper end mass increases, the balance can be achieved by shortening its length accordingly. ?

How is the space elevator powered? To realize tens of thousands of kilometers of long-distance power transmission, wireless transmission can be used. Actually, the electricity consumption is not very large. When starting, after reaching a certain speed, kinetic energy can be converted into potential energy. If it exceeds the synchronous track, the elevator is pulled up by centrifugal force, and the estimated speed can reach 200 km/h. Even at this speed, it will take 500 hours to rise from the ground to 654.38+ 10,000 kilometers. After reaching this height, it will be fine.

Why hasn't the space elevator been built yet? Because it is very difficult, the tensile strength of the material is very high. As I said just now, above the synchronous orbit, centrifugal force pulls up, and below the synchronous orbit, gravity pulls down. If the strength is not enough, the elevator will be pulled off, half flying into space and half crashing back to the ground. If steel is used as the material, the tensile strength of steel is only one thousandth of the required value, which is far from meeting the requirements.

The structure of the space elevator is stuck in the material. The ideal material is light weight and high tensile strength. People have been studying it for nearly a century. Until 199 1, Japanese physicists discovered carbon nanotubes. This kind of material is called "supernatural material" and is characterized by its light weight, which is only one sixth of that of steel. The tensile strength of the space elevator made of it can reach 300GP, which is necessary.

But carbon nanotubes are still in the experimental stage, and the length can only be made very short. At present, the latest scientific research achievement in Tsinghua University, the longest carbon nanotube in the world is only half a meter long. It is not realistic to make a tens of thousands of kilometers of space elevator. Nevertheless, with the efforts of scientists, there will be a breakthrough one day.