Space elevators still '25 years away' from reality
2024-08-24
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Image caption: The space elevator designed by Japan's Obayashi Group
Image description: Concept map of space elevator published on the British website New Scientist
Our special correspondent Chen Yang
In the sci-fi movie "The Wandering Earth 2" released last year, the climax of the first half is the fierce fight on the space elevator. In fact, as early as 2012, the famous Japanese construction company Obayashi Corporation proposed a plan to build a space elevator, which was scheduled to start construction in 2025 and be completed in 2050. Now that the time node is approaching, how is the project progressing? After interviewing the company and industry experts, many foreign media lamented that the space elevator seems to be "still 25 years away" from reality.
Building a space elevator in several steps
The Nihon Keizai Shimbun reported recently that after Obayashi completed the construction of the 634-meter Tokyo Skytree in 2012, it ambitiously proposed a plan to build a space elevator, setting a goal of starting construction in 2025 and completing it in 2050. However, at the Tokyo International Information Technology Exhibition held in June 2024, Yasuhiro Fuchida of the Future Technology Creation Department of the Technical Headquarters of Obayashi, who is responsible for the development of the space elevator project, admitted in a speech entitled "Oabashi's Space Elevator and Its Prospects" that there are still a lot of issues that need to be solved and there is still a long way to go before construction.
According to reports, the earliest idea of a space elevator was proposed by Konstantin Tsiolkovsky, a Russian scientist known as the "Father of Spaceflight" in 1895. Inspired by the Eiffel Tower in Paris, he envisioned building a super-high iron tower on the ground, directly connected to the geosynchronous orbit, and then taking the elevator inside to enter outer space.
Tsiolkovsky's idea has undergone several changes since then, and now the concept of the space elevator has been basically finalized: connecting the space station and the earth's surface through super-strong cables, people and goods can be easily transported back and forth between heaven and earth. Obayashi's detailed design is to build an "Earth Port" base on the equatorial sea surface, and connect space facilities at different orbital altitudes through cables made of carbon nanotube materials. For example, a "low-Earth orbit satellite launch gate" is arranged in the low-Earth orbit at an altitude of about 300 kilometers, from which artificial satellites transported from the earth can be released into orbit; a "geostationary orbit station" is set up in the geostationary orbit at an altitude of 36,000 kilometers, consisting of living units, experimental units, and extravehicular experimental units; a counterweight is set up at the top of 96,000 kilometers to balance the entire structure. In addition, experimental facilities such as the "Mars Gravity Center" and the "Moon Gravity Center" (gravity is equivalent to that on Mars or the Moon) will be set up according to the gravity conditions at different altitudes. According to Obayashi's plan, it will take about a week from the ground to reach the geostationary orbit by taking an "elevator" at a speed of about 200 kilometers per hour.
Obayashi even clearly proposed a specific construction method: first, assemble the spacecraft for the space elevator at an altitude of 300 kilometers, then move the spacecraft to the geostationary orbit, release the carbon nanotube cable from the spacecraft, connect and fix it to the ground, and then install the elevator on the cable. The elevator shuttles between the ground and space to transport materials and build facilities such as space stations. Fuchida Yasuhiro said: "It is estimated that the cable reinforcement will take a total of 510 times, and it will take about 20 years to complete."
The most ideal means of transportation between heaven and earth
The US website Business Insider said that the space elevator is a "dream transport from the earth to space". The biggest problem for humans to enter space at present is that the cost is too high. It is extremely expensive to send humans and materials to space with traditional rockets. For example, NASA estimates that each launch of the four Artemis moon missions will cost $4.1 billion. Even the Falcon 9 reusable launch vehicle of the US Space Exploration Technology Company, which currently has the lowest launch cost, has an average launch cost of $1,227 per pound (about $2,700 per kilogram). This is because using traditional rockets to enter space requires carrying a lot of fuel, but the fuel itself is very heavy, which in turn increases the amount of fuel that needs to be carried, forming a vicious circle. For space infrastructure that requires large-scale transportation of building materials, this defect of traditional rockets is simply unbearable. In contrast, space elevators do not require rockets or fuel, and almost perfectly avoid this defect. Space elevators are usually designed to use electromagnetic technology to power the elevators. They can use solar energy or microwave technology to transmit electricity over long distances, thereby eliminating the need for fuel.
According to the report, the space elevator project report published by Obayashi's Future Technology Creation Department mentioned that the space elevator can reduce the cost of transporting goods to space to $57 per pound. Other institutions have estimated the overall transportation cost of the space elevator to be $227 per pound, which is much lower than the cost of conventional launch vehicles. In addition, traditional rockets are limited by the size of the fairing and can only carry a small amount of load. The space elevator has much smaller restrictions in this regard. At the same time, the elevator runs slower than the rocket, but it can reduce vibration, which is very important for sending sensitive equipment into orbit.
Carbon nanotube manufacturing technology is still immature
The Nihon Keizai Shimbun said that the space elevator had previously remained in the fantasy stage because of the lack of lightweight and strong materials needed to manufacture ultra-long cables connecting the earth and space. The cables must be very strong to withstand their own huge weight and the tension caused by space facilities. According to calculations, the performance of conventional metal materials such as steel is far from meeting the needs of space elevator cables. The heat generated by the friction between the elevator and the cable is another problem: in the vacuum of space, heat is difficult to dissipate.
But this situation changed in 1991 - the lightweight and high-strength carbon nanotube material was discovered, and the space elevator has since become feasible. According to reports, in theory, the strength of carbon nanotubes can reach up to 200Gpa, which means that 200 carbon nanotubes thinner than a hair can pull up a car. It has the advantages of both polymers and metals, with a density of only 1/6 of steel, but an elastic modulus of 5 times that of steel, a tensile strength of 100 times that of steel, and thermal conductivity at room temperature far exceeding other metal materials. Therefore, carbon nanotubes are also considered by Obayashi Group to be an ideal material for manufacturing ultra-high-strength cables for space elevators.
However, according to Obayashi's plan, the cables of future space elevators are not made by combining multiple carbon nanotubes to increase strength, but by making single carbon nanotubes with a length of 96,000 kilometers and molecules connected to each other. At the Tokyo International Information Technology Exhibition held in June, relevant persons in charge revealed that currently only carbon nanotubes less than 1 cm in length that meet relevant requirements can be made. Therefore, the report admits that Obayashi is still studying the large-scale preparation process of carbon nanotubes as cable materials.
Facing more technical challenges
The American website "Fun Engineering" mentioned that in addition to the lack of suitable cable materials, the space elevator also faces various other technical challenges. For example, there are more and more space debris in space, and the threat to spacecraft in orbit continues to increase. At present, the International Space Station mainly adjusts its operating altitude to avoid possible collisions, but for the space elevator superstructure, which is much more massive than the International Space Station, it is much more difficult to adjust the operating orbit. At the same time, the cables of the space elevator are also facing the threat of space debris impact, the continuous influence of strong cosmic radiation and drastic temperature differences, and extreme weather such as storms and lightning strikes in the atmosphere. There is no clear plan on how to deal with these challenges.
In addition, in order to ensure that the space part of the space elevator is synchronized with the ground part, it needs to be built on the equator. Currently, most countries with relevant aerospace construction capabilities are located in the northern hemisphere. Coupled with the huge supporting facilities and the staggering amount of engineering, the space elevator has certain requirements for nearby transportation conditions, which is also the main consideration for Obayashi Group to choose the offshore base for its construction. However, the "Fun Engineering" website mentioned that the climate change at sea is large and may be hit by storms. At the same time, the related security challenges are also large and vulnerable to terrorist attacks at sea. Finally, the related construction costs are extremely expensive, and Obayashi Group estimates the cost to be more than 1 trillion yen (about 6.8 billion US dollars).
Therefore, although Canadian physicist Stephen Cohen and others optimistically estimated at the beginning of this century that it would only take 20 to 30 years to make the space elevator a reality, Fuchida Yasuhiro now admits that the project requires cooperation from all parties and is still looking for partners. ▲#Deep Good Articles Project#
