Space elevators are seen as a way to transport people and supplies to stationary satellites. The possible pay-off is as simple as could be — a space elevator could bring the cost-per-kilogram of launch to geostationary orbit from $20,000 to as little as $500. In 2012, Tokyo-based Obayashi Corp. announced plans to build a space elevator by 2050. The concept has also caught the attention of Google X, in the past, as well as an X Prize competition. The China Academy of Launch Vehicle Technology, a division of the China Aerospace Science and Technology Corp., also announced in 2017 that it plans to have an operational space-elevator system by 2045.
Countries including China, the United States, Russia and Japan continue to support the research. So-called space tether technology has the potential to be used for military purposes, including capturing “non-cooperative targets” including enemy satellites.
A group of researchers conducted a test to develop technology for a space elevator that would link the Earth and outer space using cables. The Japan Space Elevator Association carried out the experiment in August 2018 at the Fukushima Robot Test Field in Fukushima Prefecture. In the test, a freighter device carrying a small robot that would be used for celestial probes ascended a 100-meter-long cable hung from a balloon. The robot jumped off the carrier and landed by parachute.
Now researchers from Shizuoka University in Japan announced that they will launch an experiment to the International Space Station. In the experiment, which will be the first of its kind in space, two ultrasmall cubic satellites, or “cubesats,” will be released into space from the station. They will be connected by a steel cable, where a small container — acting like an elevator car — will move along the cable using its own motor. A camera attached to the satellites will record the movements of the container in space, according to the Japanese newspaper The Mainichi. Each cubesat measures just under 4 inches (10 centimeters) on each side. The cubesats will be connected by a 33-foot-long (10 meters) steel cable for the “elevator car” to move along, according to the report. While experiments to extend a cable in space have been conducted before, the new Japanese experiment will be the first test to move a car-like container on a cable in space. Obayashi Corp. estimates the total cost of a fully functional, first-generation space elevator to be 10 trillion yen (about $90 billion) — almost the same as that for the maglev train project connecting Tokyo and Osaka.
New report from the International Academy of Astronautics (IAA) has predicted that new ribbon will be able to carry up to seven 20-ton payloads at once. It will serve as a tether stretching far beyond geostationary (aka geosynchronous) orbit and held taught by an anchor of roughly two million kilograms. Sending payloads up this backbone could fundamentally change the human relationship with space — every climber sent up the tether could match the space shuttle in capacity, allowing up to a “launch” every couple of days. Association head Shuichi Ono says scientists previously had no place to conduct large-scale field tests. Ono also says the association wants to conduct more such tests to nurture space development technology in the prefecture.
A research team from Tsinghua University in Beijing has developed a fibre they say is so strong it could even be used to build an elevator to space. They say just 1 cubic centimetre of the fibre – made from carbon nanotube – would not break under the weight of 160 elephants, or more than 800 tonnes. And that tiny piece of cable would weigh just 1.6 grams. “This is a breakthrough,” said Wang Changqing, a scientist at a key space elevator research centre at Northwestern Polytechnical University in Xian who was not involved in the Tsinghua study.
A space elevator is a proposed type of planet-to-space transportation system. The main component would be a cable (also called a tether) anchored to the surface and extending into space. The design would permit vehicles to travel along the cable from a planetary surface, such as the Earth’s, directly into space or orbit, without the use of large rockets.
An Earth-based space elevator would consist of a cable with one end attached to the surface near the equator and the other end in space beyond geostationary orbit (35,786 km altitude). The competing forces of gravity, which is stronger at the lower end, and the outward/upward centrifugal force, which is stronger at the upper end, would result in the cable being held up, under tension, and stationary over a single position on Earth. With the tether deployed, climbers could repeatedly climb the tether to space by mechanical means, releasing their cargo to orbit. Climbers could also descend the tether to return cargo to the surface from orbit
There are number of technological impediments to a space elevator, but by far the most important is the tether itself; materials science has still to invent a substance that could provide the strength, flexibility, and density needed for a space elevator.
To construct a space elevator on Earth the cable material would need to be both stronger and lighter (have greater specific strength) than any known material. Development of new materials that meet the demanding specific strength requirement must happen before designs can progress beyond discussion stage. Carbon nanotubes (CNTs) have been identified as possibly being able to meet the specific strength requirements for an Earth space elevator, but they have only about a tenth of the necessary strength-to-weight ratio and cannot be made into filaments more than a few centimetres long, let alone thousands of kilometres. Other materials considered have been boron nitride nanotubes, and diamond nanothreads that might be stronger, but their properties are still poorly understood.
Those cables would need to have tensile strength – to withstand stretching – of no less than 7 gigapascals, according to Nasa. In fact, the US space agency launched a global competition in 2005 to develop such a material, with a US$2 million prize attached. No one claimed the prize. Now, the Tsinghua team, led by Wei Fei, a professor with the Department of Chemical Engineering, says their latest carbon nanotube fibre has tensile strength of 80 gigapascals. Carbon nanotubes are cylindrical molecules made up of carbon atoms that are linked in hexagonal shapes with diameters as small as 1 nanometre. They have the highest known tensile strength of any material – theoretically up to 300 gigapascals. “If the cable is not strong enough, it would not even be able to support its own weight. Until now, there has been no material tough enough to do the job,” said Wang, deputy executive director of the China-Russia International Space Tether System Research Centre.
But for practical purposes, these carbon nanotubes must be bonded together in cable form, a process which is difficult and can affect the overall strength of the final product. According to Wang, the space lift researcher, the transport system would need more than 30,000km of cable, and it would also need other structures such as a rail and a shield to protect against space debris and other environmental hazards.
The material would have to withstand the weather disturbances of troposphere, and the vehicles running up and down it could also cause dangerous oscillations. Climbers cover a wide range of designs. On elevator designs whose cables are planar ribbons, most propose to use pairs of rollers to hold the cable with friction. Climbers would need to be paced at optimal timings so as to minimize cable stress and oscillations and to maximize throughput. Anchoring it to a moveable, seagoing platform might help, but keeping the cable steady would still be a tall order. Space debris is another problem from an altitude of around 2,000km upwards, as collision with any of them could be disastrous.
Chinese and Russian space scientists, for instance, are working together to find a safe, effective way to lower a fine, feather-light cable from a high-altitude orbit to the ground. Re-entry to the atmosphere can produce a lot of heat that could burn the cable, while the counterweight may need to be as large as an asteroid to keep the line straight.
Both power and energy are significant issues for climbers—the climbers would need to gain a large amount of potential energy as quickly as possible to clear the cable for the next payload. Various methods have been proposed to get that energy to the climber:
- Transfer the energy to the climber through wireless energy transfer while it is climbing.
- Transfer the energy to the climber through some material structure while it is climbing.
- Store the energy in the climber before it starts – requires an extremely high specific energy such as nuclear energy.
- Solar power – After the first 40 km it is possible to use solar energy to power the climber
Wireless energy transfer such as laser power beaming is currently considered the most likely method, using megawatt powered free electron or solid state lasers in combination with adaptive mirrors approximately 10 m (33 ft) wide and a photovoltaic array on the climber tuned to the laser frequency for efficiency. For climber designs powered by power beaming, this efficiency is an important design goal. Unused energy would need to be re-radiated away with heat-dissipation systems, which add to weight.
Yoshio Aoki, a professor of precision machinery engineering at Nihon University and director of the Japan Space Elevator Association, suggested including a second cable and using the conductivity of carbon nanotubes to provide power.
This report lays out a. Existing technologies will be little help; tethers from the EU and Japan are beginning to push the 100-kilometer mark, but that’s still a long way off orbital altitude, and the materials for existing tethers will not allow much additional length.
Projecting current research in carbon nanotubes and similar technologies, the IAA estimates that a pilot project could plausibly deliver packages to an altitude of 1000 kilometers (621 miles) as soon as 2025. With continued research and the help of a successful LEO (low Earth orbit; anywhere between an altitude of 100 and 1200 miles) elevator, they predict a 100,000-kilometer (62,137-mile) successor will stretch well past geosynchronous orbit just a decade after that.
Building a space elevator between the moon’s surface and lunar orbit (to transport things such as visiting tourists or material mined on the moon) would be far easier, because of the weaker gravity and lack of atmosphere.