It takes 14 days to reach the moon and 61 days to reach Mars! How far is the dream of a "space elevator"?

The "space elevator" in the novel "The Three-Body Problem" is fascinating. Just get into the elevator, press a button, and you'll be in space in a flash. The dream of this kind of space elevator has a long history. In 1895, Russian scientist Tsiolkovsky proposed the idea of ​​a space elevator after seeing the Eiffel Tower. In 1979, science fiction master Clarke also described a space elevator in his novel "The Fountains of Paradise."

Peter Swan, chairman of the International Space Elevator Alliance, also said that in the future, space elevators will be permanent logistics infrastructure that can transport materials and personnel into space and become a new channel for entering space. He also further pointed out that since the gravity level of the moon and Mars is lower than that of the earth, the air is thinner or vacuum, and the construction difficulty is easier than on earth. In the future, it will take 14 days to reach the moon and 61 days to reach Mars.

Next, we have to ask, what stage has the space elevator technology progressed to, and when can it be realized? If an idea is divided into 10 stages of technological maturity from science fiction to reality, from 0 to 9, we are now in the second stage. Beyond the science fiction stage (stage 0), a scientifically feasible principle has been proposed, and the main feasible technical indicators have been calculated. Later, experimental verification of key technologies and systems will be required, and finally actual construction will be carried out. It can be seen that there is still a long way to go.

The picture comes from Tuchong.com

So, what are the specific scientific principles that make this space elevator possible, and what structural components does it include?

The essence of a space elevator is to build a permanent "cable" building that connects the ground to a certain point in space. If the cable building is lower than 36,000 kilometers, then it will be under pressure inside. Assuming it is built with steel, it can only be built about 9 kilometers high, which is about the height of an airplane. If it is higher, the steel at the bottom will be crushed under the huge pressure. However, the ability of various materials to withstand stretching far exceeds their ability to withstand compression. Therefore, a plan for a space elevator about 50,000 kilometers long was proposed. This plan is similar to an athlete throwing a hammer. The earth is equivalent to a hammer thrower. A 50,000-kilometer cable is fixed at the equator of the earth, with a hammer at the end. Due to the rotation of the earth, the rotational centrifugal force of the hammer and cable is balanced with the gravity they are subjected to.

So the entire space elevator system is composed of four parts: the first is a base station anchored on the equatorial surface, the second is a cable with a length of about 50,000 kilometers, the third is a balance weight located at an altitude of 50,000 kilometers, this counterweight can be a space station, and the fourth is the elevator car that runs up and down quickly along the cable.

Some people estimate that the cost of building a space elevator is about 10 billion US dollars. However, after it is built, it will only cost 100 US dollars to transport 1 kilogram of objects into space. The transportation cost is 100 times lower than that of a launch vehicle. As long as 1,000 tons of objects are transported into orbit, the construction cost of the space elevator will be recovered. With such a bright application prospect, why not build it quickly?

This is because there are still many technical difficulties. The biggest difficulty is that materials with sufficient strength are needed. Carbon nanotubes and super-strong graphene are considered to be ideal materials for building space elevator cables. Their strength is sufficient, but only carbon nanotubes less than 1 meter long can be produced in the laboratory, which is still a long way from 50,000 kilometers long. It is really a long march of ten thousand miles and less than one step. In addition, there are still many details to be answered: What drive mode should the space elevator car choose? How can a 50,000-kilometer-long cable effectively resist swinging? What should the space elevator do when it encounters space debris and meteoroid impacts?

In short, taking a space elevator into space is still in the theoretical stage, and there are still many technical difficulties to be overcome before the actual project implementation!

This article is a work supported by Science Popularization China Starry Sky Project

Author: Zhou Binghong

Review: Liu Yong

Produced by: China Association for Science and Technology Department of Science Popularization

Producer: China Science and Technology Press Co., Ltd., Beijing Zhongke Xinghe Culture Media Co., Ltd.