On the occasion of the Spring Festival in the Year of the Rabbit, the latest domestic sci-fi film "The Wandering Earth 2" was released in anticipation, compared with "The Wandering Earth", which created a new milestone in Chinese science fiction 4 years ago, as a sequel, "The Wandering Earth 2" is full of hardcore sci-fi style, and continues to impact the audience's senses through grand and shocking special effects lenses. The space elevator that appears at the beginning of the movie that leads directly to the sky, its powerful functions, realistic special effects, detailed details, and magnificent scenes, has become one of the plots that are hotly discussed by fans.
(Source: The space elevator that appeared in the trailer of "The Wandering Earth 2")
The sci-fi concept of space elevator is actually a frequent guest in Liu Cixin's works. In the well-known "Three-Body Problem", Da Liu described in detail this strange device that helped humans ascend into space. In "The Wandering Earth 2", the crew used concrete lens language to fully present it in front of the audience.
In fact, the "space elevator" itself is not just a pure science fiction concept, but also a direction that scientists and engineers strive to achieve. Many times, the boundary between science fiction and science is so hazy, will human beings really reach the "other side" of space easily by taking an elevator as depicted in science fiction?
Science fiction writers inspired by scientists
At the 2022 International Symposium on the Peaceful Use of Space Technology (Health) held 2 months ago in "The Wandering Earth 2", Peter Swan, president of the International Space Elevator Federation and academician of the International Academy of Astronautics, proposed that in the future, as a permanent logistics infrastructure, space elevators can transport materials and personnel to space and become a new channel into space. Throughout history, although the space elevator has been a topic that many science fiction writers talk about, and has appeared in different forms in a considerable number of science fiction works, scientists known for their rigor in exploring the "space ladder" are far ahead of novelists.
▲British writer Arthur Sir Clark first depicted the "elevator to the sky" in the science fiction novel Fountain of Heaven
As early as 1895, Russian rocket expert and space pioneer Tsiolkovsky was inspired by the construction of the tower when visiting the Eiffel Tower in Paris, France, and proposed to build an ultra-tall iron tower on the ground that reaches geosynchronous orbit to achieve access to outer space by erecting an elevator. He also made a detailed design of this tower and calculated its height to be 35,786 km. Tsiolkovsky's biblical Babel design is a metaphor for the "space elevator." However, after a series of calculations, he came to the conclusion that the construction of such a supertall iron tower is impossible.
In the 60s of the 20th century, with the first human entry into space, the idea of building a space elevator into space was once again proposed by scientists. Soviet engineer Yuri Artsuitanov envisioned the construction of an "electric train" between open space to realize space logistics transportation, unlike Tsiolkovsky's idea of simply building towers from the ground with steel structures, he proposed a plan for building from space to the ground, that is, first launch a geosynchronous satellite, and then extend a rope from the satellite to hang down to the ground, and form an "electric train" running track after fixing at one end of the ground.
In 1970, American scientist Jerome Pearson first theorized the concept of "space elevator" and published his related arguments in the Journal of Space Engineering. Similar to the Soviet Union's "electric train" scheme, Pearson envisions "hanging" several cables of special materials and high tensile strength from artificial vehicles in space to the ground, as the main structure of the space elevator, in this similar way to "dragging a kite" to achieve the elevator to the sky. Pearson's idea basically laid the foundation for the evolution of space elevators in academia. Subsequently, Pearson extended this concept to the moon, he demonstrated in detail the idea of the Earth-Moon space elevator at an academic conference, and summarized the main structure of the space elevator as the concept of "space line", in Pearson's vision, the future "space line" is a slender cable made of Kevlar fiber or other high-strength materials only slightly thicker than the lead of a pencil.
Pearson in his twilight years with his vision for a space elevator (Image: The Washington Post)
Although Pearson uses quite complex scientific theories to demonstrate the future feasibility of space elevators and their low cost relative to launch vehicles. But since mankind entered the space age, rockets are the only technically feasible vehicles to ascend to the sky. Although Pearson's scientific argument has received widespread attention from the academic community, the space elevator is a concept far ahead of its time, so he himself has been ridiculed by peers with snarky words such as "it is better to write science fiction". Interestingly, Pearson's ideas really influenced the world of science fiction, when the British writer Arthur A. Bush, who lived in Sri Lanka at the time, actually influenced the world of science fiction. Sir Clark was inspired by his idea of the "line of space" and first depicted the "elevator to the sky" in his 1979 science fiction novel The Fountain of Heaven.
Insurmountable technical difficulties
During the years of the space race, no effort was spared to increase the thrust and payload of launch vehicles in the hope of achieving more efficient space transportation. Although the construction and operating costs of rockets are huge, the biggest advantage of rockets compared to space elevators lies in "technical feasibility", from liquid/solid fuel engines, to aerodynamic shapes to navigation communications, rockets as a set of systematic engineering has been repeatedly practiced for decades. Although Pearson and other advocates tirelessly demonstrated the convenience and affordability of space elevators, at the time, it seemed that from paper data to engineering practice, the space elevator itself still had too many problems to overcome.
(Source: "The Wandering Earth 2" movie poster part)
The biggest challenge is the material problem of the elevator. Starting from Tsiolkovsky's ultra-tall tower, in order to offset the impact of the Earth's rotation and ensure that the space elevator does not displace relative to the ground facilities, scientists have locked the construction site in geosynchronous orbit when demonstrating the space elevator.
According to the space elevator envisaged by Pearson, if ordinary steel cables are used as the main material, then if such a steel cable hangs from the geosynchronous orbit to the ground, the steel cable will be pulled off by its own weight less than 9,000 meters, and the geosynchronous orbit can be more than 30,000 kilometers away from the ground. When Pearson demonstrated the concept of "space line", he only vaguely proposed the use of high-strength materials as the main structure of the space elevator. The specific use of which fiber material was an insurmountable problem from the demonstration stage at that time.
Secondly, from geosynchronous orbit to the ground, it is necessary to pass through the atmosphere of more than 1,000 kilometers, the complex climatic conditions of the troposphere, the increasing temperature of the stratosphere with the increase of altitude, etc., coupled with the gravitational action from the moon and the sun, all directly or indirectly test the stability of the space elevator. In addition, when taking the elevator to space, passengers will pass through high-intensity radiation belts in the outer layer of the earth, and how to protect passengers from being affected is another engineering problem.
▲ Pearson's original space elevator imagination (Image source: STAR.INC)
In addition, considering that one end of the space elevator needs to be "tethered" to geosynchronous orbit, and the other end needs to erect a base station near the Earth's equator, how to select a site for the base station is also difficult. The land around the equator is mostly tropical rainforest, the construction of elevator base stations is very difficult, and from the cost of transportation is not cost-effective, then only on the high seas to build floating base stations, Pearson and his later people have proposed similar ideas, but how to ensure the stable operation of such a huge elevator base station under complex sea conditions is also a problem.
A silver lining for the future
Since entering the 90s of the last century, materials science has made a series of major breakthroughs, which has allowed space elevator proponents to see the dawn of solving the material problem. In 1993, carbon nanotubes were born and mass-produced two years later, a material with high strength (similar to diamond), good flexibility, and can be made into fibers, which is very suitable for making the "space line" proposed by Pearson. As one of the strongest materials known in the world, the intrinsic tensile strength of carbon nanotubes is as high as 100GPa (pressure unit, that is, jipaska, 1 GPa=1000 000 000Pa), and the tensile strength per unit mass is 276 times that of steel, which can theoretically achieve the effect of "four or two thousand pounds", which is very in line with Pearson's idea that "the space line is only slightly thicker than the pencil lead".
Of course, with the current production technology of carbon nanotubes, it is still a long way from their application in the construction of space elevators. For example, because the catalyst used to prepare carbon nanotubes is easily inactive at high temperatures, the length of carbon nanotubes is greatly limited. The cable length required for the space elevator is more than 30,000 kilometers. However, in the forward direction of carbon nanotubes, all countries are working hard to explore, among which the mainland has made a major breakthrough in recent years.
At the 2010 National Space Elevator Conference, former Soviet engineer Yuri Artutanov visited the future space elevator design scheme (Image source: The Space Elevator Blog)
In 2013, after carrying out a large number of studies on the growth mechanism, structural controllability, and performance characterization of ultra-long carbon nanotubes, the scientific research team led by Wei Fei, a professor of chemical engineering at Tsinghua University, prepared the world's first carbon nanotubes with a length of more than half a meter for the first time, setting a new world record. This opens up the possibility of building the cables needed for space elevators in the future. Professor Wei Fei once said: "The carbon nanotubes we prepared have perfect structure, excellent mechanical properties and macroscopic length, and we are currently engaged in the preparation of carbon nanotubes of more than one meter, and the next step is to prepare carbon nanotubes with macro density of more than kilometer length." These works will open a ray of light for the preparation of space elevators! ”
It is in recent years that some cutting-edge technologies have made major breakthroughs in succession, and the space elevator, which was originally just a flashing between science and science fiction, has begun to be brought into the engineering design blueprint by scientists. In 1999, NASA's Marshall Research Center published a report entitled "Space Elevators, Advanced Infrastructure in Space", which demonstrated the feasibility of space elevators in detail from an official perspective, which was the first time that the concept of "space elevators" was officially recognized.
▲ NASA released a future space elevator scenario (Image source: NASA)
Since then, from major aerospace official agencies to many companies interested in investing in the space industry, they have launched their own space elevator plans, such as Russia has planned to cooperate with the European Space Agency to build a space cargo elevator, the United States has set up a company called Lift Port Group to develop space elevators, and Japan has also announced the design of ladder cables.
Of course, the design scheme of these space elevators proposed so far still has quite a lot of technical problems, but after all, human beings have opened up another idea of connecting space and earth in addition to launch vehicles. I believe that with the continuous iterative development of technology, the relevant difficulties are gradually solved, such as the shocking scene of the space elevator transporting personnel and materials to space in "The Wandering Earth 2", which may not be far away from us.
(Source: "The Wandering Earth 2" movie poster part)