A New Method for Making Graphene has an Awesome Application: A Space Elevator!
The Space Elevator is one of those ideas that seems to have an endless supply of lives. Originally proposed about a century ago, this concept calls for a tether of supermaterial that connects a station in orbit to Earth's surface. Our planet's rotation would keep this tether taught, and a system of "climbers" would transport people and payloads to and from space. The engineering challenges and costs associated with such a structure have always been enormous. But every generation or so, new research comes along that causes engineers and space agencies to reevaluate the concept.
The single-greatest challenge has always been the tether since no known material has ever been strong enough to handle the stresses involved. But as it turns out, this issue may finally be resolved! According to scientists with the International Space Elevator Consortium (ISEC), a cost-effective manufacturing process could produce graphene ribbons that are strong enough to fashion a tether! Their latest findings are detailed in a paper they will present at the upcoming 2022 International Astronomical Congress in Paris.
The research was led by Adrian Nixon, a graphene and 2D materials scientist, a Royal Society of Chemistry member, founder and editor of Nixen Publishing, and a board member of StellarModal and the ISEC. He was joined by Dennis Wright - the Vice President of the ISECIBM and a former researcher with the Stanford Linear Accelerator Center (SLAC) National Accelerator Laboratory - and Dr. John Knapman, a former AI specialist with IBM, a member of the British Interplanetary Society, and the Managing Director of the ISEC.
Nixene's flagship publication (the Nixene Journal) is an affiliate member of the University of Manchester's Graphene Engineering Innovation Centre (GEIC). This engineering facility specializes in the rapid development and scaling-up of graphene and other 2D materials.
Like most time-honored revolutionary ideas for space exploration, the Space Elevator can be traced to Russian/Soviet rocket scientist Konstantin Tsiolkovsky (1857-1935). Considered to be the top contender for the title of the "Father of Rocketry" (the other two being Hermann Oberth and Robert Goddard), Tsiolokovsky is responsible for developing the "Rocket Equation" and the design from which most modern rockets are derived. In his more adventurous musings, he proposed how humanity could build rotating Pinwheel Stations in space and a Space Elevator.
This proposal was inspired by his visit to Paris in 1895, where he witnessed the Eiffel Tower for the first time (construction had finished in 1889). From this encounter, Tsiolkovsky conceived of a structure that reached to geostationary orbit (GSO), or an altitude of 36,000 km (22,370 mi). However, Tsiolkovsky's version of the idea called for a compression structure rather than a suspension one. He also noted that the idea was unrealistic since no known material was strong enough to support the weight of the standing structure.
By the onset of the Space Age, the idea was reexamined by Soviet and American scientists as a suspension structure. Examples include Soviet Engineer Yuri Artsutanov's (1959) proposal for an "Electric train to the Cosmos" and the "Sky-Hook" proposed by a team of American engineers in 1966. These and other versions involved several shared design elements, starting with an "Anchor" attached to a fixed point on land or a mobile platform at sea. The "Tether" would extend from this to a "Counterweight" in space, which could be a captured asteroid, a space station beyond GSO, or a combination thereof.
A series of "Climbers" (or cable cars) would deliver crews and payloads to orbit, which could be powered by solar panels, nuclear reactors, wireless, or direct energy transfer. Since the early Space Age, the concept has remained largely unchanged, as have the proposed benefits of such a structure.
The enduring popularity of the Space Elevator is easy to grasp in light of the benefits having one would entail. The most obvious is the ability to send payloads and people to space for a fraction of the cost of launching them via rockets. It would also allow us to build spacecraft and space stations in orbit, eliminating the need to fabricate their respective components or modules on Earth and launch them to space using heavy-lift rockets. This process has never been cheap!
Between 1970 and 2000, launch costs remained relatively consistent at an average of ~$18,500 per kg ($8,400 per lb). Thanks to the development of reusable rockets like SpaceX's Falcon 9 and Falcon Heavy, that price has dropped to $1,410 and $2,719 per kg ($640 and $1,235 per lb). According to an analysis conducted by Tyson M. Sparks (University of Colorado, York Space Systems LLC) in 2014, the cost of sending payloads to orbit with a Space Elevator could be as little as $113 per lb ($250 per kg).
As Nixon explained to Universe Today via email, another benefit is how a Space Elevator is a "green technology" that can deliver massive payloads to orbit without the environmental impact of rocket launches. Based on current research, a single rocket launch can release up to 300 tons of carbon dioxide into the upper atmosphere. Given the growing demand for satellite launches, broadband internet, and commercialization of Low Earth Orbit (LEO), could become the greatest driver of anthropogenic climate change.
In contrast, the railcars do not produce harmful greenhouse gas emissions and can be powered by a combination of space-based solar and nuclear reactors. Moreover, a Space Elevator would reduce the cost per kilo of transferring payloads to orbit and be much more efficient than hundreds or thousands of rocket launches. Said Nixon:
"Rockets are very good at delivering small amounts of high-value payloads into space, fast. The space economy is developing rapidly with plans for missions such as a Mars colony, a Lunar village, and space solar power. The planned missions require large amounts of mass lifting from the surface of the Earth to space. However, the key limitation of rockets is their inability to scale to deliver large amounts of mass to space, sustainably. The rocket equation means even a SpaceX StarShip (the most efficient rocket system) can only deliver 2% of the mass on the launchpad to low earth orbit."
These echo one of the most well-publicized aspects of "Space Age 2.0," which is the promises made by entrepreneurs like Musk, Bezos, Branson, and others. Among them, there's the promise of "building a road to space," increasing access through commercialization and establishing the first human outpost on Mars. But as Nixon added, the enduring issues of cost, inefficiency, and environmental impact of rocket launches mean that these promises will go unfulfilled. "The space elevator has the ability to lift massive cargo and deliver it daily, inexpensively, safely, routinely, and in an environmentally neutral approach - fulfilling these mission promises," he said.
"Our team believes that the development of the Space Elevator permanent space access infrastructure is a MUST for humanity to save the atmosphere and enable a bold movement off-planet," added ISEC President and Director Dr. Swan. "Rockets are our historic approach to these dreams, but they do not have the power nor the reach to match the needs of humanity. The rocket equation is a killer of dreams - extremely low delivery statistics and damage along the way to our atmosphere. We MUST do the space elevator. We believe there is a collaboration and cooperation between advanced rockets and space elevators that will be our future."
The "Tether Problem"
Unfortunately, every previously-proposed evaluation of the concept has had an Achilles Heel. In short, a Space Elevator has not been feasible in the past few decades since no known material had the tensile strength to support the structure's weight. In 1979, Arthur C. Clarke summarized the problem during his address to the 30th International Astronautical Congress (IAC), titled "The Space Elevator: 'Thought Experiment, or Key to the Universe?'":
"How close are we to achieving this with known materials? Not very. The best steel wire could manage only a miserable 31 mi (50 km) or so of vertical suspension before it snapped under its own weight. The trouble with metals is that, though they are strong, they are also heavy; we want something that is both strong and light. This suggests that we should look at modern synthetic and composite materials. Kevlar... for example, could sustain a vertical length of 124 mi (200 km) before snapping - impressive, but still totally inadequate compared with the 3100 (5000) needed."
With the development of carbon nanotubes (CNs) in the 1990s, there was a renewed interest in Space Elevators. In June 1999, David Smitherman of the NASA Advanced Concepts Office (ACO) delivered a speech at the Advanced Space Infrastructure Workshop, proposing that CNs could make a space elevator feasible. His arguments were also published in a 2000 report titled "Space Elevators: An Advanced Earth-Space Infrastructure for the New Millennium."
That same year, NASA scientist Bradley C. Edwards performed a feasibility study with support from the NASA Institute for Advanced Concepts (NIAC). In his final report (titled "The Space Elevator"), he stated that carbon nanotubes were the best candidate since they were believed to have the necessary tensile strength and density - 130 gigapascals (GPa) and 1300 kg/m³, respectively. In 2003, he followed up with the NIAC Phase II Final Report, which contained similarly optimistic appraisals. However, his conclusions were based on theory and simulation and did not consider two major issues with CNs.
These included the issue of mass production since CNs are grown and not machine-produced, with a maximum length of about 50 cm (20 inches) - achieved by researchers at Tsinghua University in Beijing. Even worse, the hexagonal covalent bonds that give carbon nanotubes their high tensile strength also mean they are likely to fray when placed under extreme stress. As Nixon summarized:
"The study reported in 2003 that the space elevator was based on solid science and could be built with today's engineering technology - just one part remained to be solved - the tether. The tether material needs to be incredibly strong and lightweight. The only material at the time was carbon nanotubes (CNT). At the time of the NIAC report in 2003 CNTs could not be made longer than a few mm. CNT development has not advanced in the last two decades - and the space community lost interest in the space elevator."
Less than a year after the NIAC Phase II report was issued, another carbon-based supermaterial that showed immense potential was isolated for the first time!
Graphene to the Rescue?
Like carbon nanotubes, graphene is an allotrope of carbon consisting of a single layer of atoms arranged in hexagonal lattice structures. Unlike CNs, graphene is a two-dimensional material arranged in a sheet. Manchester University professors Andre Geim and Konstantin Novoselov discovered the material and were awarded the 2010 Nobel Prize in Physics "for groundbreaking experiments regarding the two-dimensional material graphene."
The material has incredible electrical properties but also incredible tensile strength. A sheet of single-crystal graphene has a tensile strength roughly 200 times that of steel - up to 130 Gigapascals (GPa) - which is well within the tolerances specified in the NAIC II Report. In 2021, Nixon and his colleagues at Nixene Publishing - Debbie Nelson (contributing editor and project manager) and Rob Whieldon (operations director) - had the opportunity to brief NASA on the potential of graphene. Their briefing, "Impossible to Industrial in 17 years," was part of the Commercial Space Lecture Series.
In this weekly teleconference, NASA meets with representatives from the commercial space sector to discuss opportunities for mutual assistance. In their presentation, they showed how graphene production had reached the point where kilometer-scale continuous graphene fibers can be produced. Examples include how in 2020, researchers at MIT developed a continuous roll-to-roll technique that could create large sheets of graphene at a rate of around 2 meters (6.5 feet) per minute. In addition, the Tennessee-based company General Graphene recently commenced operations, using the CVD method to produce polycrystalline graphene.
And in Korea, the industrial company Charmgraphene has announced that it can manufacture polycrystalline graphene sheets at speeds of 2 meters (6.56 ft) per minute and lengths of 1 km (0.62 mi). These companies are all producing polycrystalline graphene intended for electronics, not the 2D single-crystal variety with the highest tensile strength. But as Dr. Swan explained, they are moving in the right direction:
"We are starting to see large area sheet graphene being manufactured. While this method had been devised to produce graphene electrodes that would allow for lightweight, flexible solar devices and display screens, the technique can be adapted to create the material for a tether."
For the sake of their most recent paper, which they will present before the 2022 IAC, Dr. Nixon and his colleagues considered the benefits of 2D single crystal graphene against other candidate materials. The key here was to weigh tensile strength against the speed and cost-effectiveness of the production process, thereby determining which supermaterial offered the highest cost-benefit balance. Said Nixon:
"We investigated three candidate materials for the study: Carbon nanotubes (CNT), Graphene, and Hexagonal Boron Nitride (hBN). hBN is another 2D material, nearly as strong as graphene and also a candidate tether material. The process for making 2D materials and CNTs is called the chemical vapor deposition (CVD) method. The CVD process uses methane gas to make graphene, and this is an inexpensive feedstock and the basis for the current industrial manufacture."
As they conclude, very little progress has been made in the manufacturing of CNs over the past three decades, the process is painfully slow, and the resulting tubes are never long enough. And while hBN is robust in terms of tensile strength and the manufacturing process is promising (typically producing 200 mm wafer-scale polycrystalline for electronics applications), it is not yet at the scale and speeds needed to create a tether. Graphene combines the best of both worlds when used to create the Single Crystal variety.
At present, Nixon and his colleagues at the ISEC estimate that enough material could be generated to manufacture at tether for a cost of $18 billion - less than NASA's 2022 budget of $24 billion. Even more encouraging, they further estimate that with the right support and development, the price for producing single crystal 2D sheets of graphene could drop to as little as 1 cent per square meter (1/10th of a cent per square foot), which would mean a tether could be built for $3.6 billion (roughly 15% of NASA's 2022 budget).
The "Green Road" to Space
Beyond evaluating materials that could make this time-honored megastructure a reality, the ISEC is also committed to making a Space Elevator happen in our lifetimes! However, the overall architecture the ISEC is envisioning (called the "Galactic Harbor") goes beyond creating a single elevator. In their 2020 ISEC position paper, titled "Space Elevators are the Transportation Story of 21st Century," they shared their vision for a series of "Galactic Harbor" installations worldwide. Each installation would consist of two elevators in the Atlantic Ocean, the Indian Ocean, and the Pacific Ocean.
The mission architecture also entails using rockets and elevators working in tandem to create a space transportation infrastructure that will facilitate "human migration" from Earth and the establishment of humanity as an "interplanetary" species. To speed the development of this architecture, Dr. Swan and colleagues Vern Hall (a transportation industry specialist and engineer) and Michael Fitzgerald (a project specialist with the USAF) launched Galactic Harbor Associates (GHA). Along with multiple research foundations and commercial partners, this company is dedicated to commencing initial operations with the first Galactic Harbor by 2037.
The benefits of the Space Harbor were spelled out by Dr. Swan and his colleagues in the 2020 ISEC position paper, as well as their more recent "Space Elevators, the Green Road to Space" study. These include being able to send 30,000 metric tons (33,069 US tons) of payloads to GSO and beyond per year, based on its initial operational capability. At full capability, it will be able to send 170,000 metric tons (187,393 US tons) to GSO at a fraction of the cost (compared to rockets) and without polluting the atmosphere. This will allow for so much more, including:
- Enabling space-based solar power while supporting the Paris Accords
- Enabling endless opportunities for commercial enterprises, research, and travel
- Lifting payloads as the Green Road to Space, helping to save our atmosphere
- Improving life on Earth with major accomplishments in space
- Enabling early completion of massive projects, such as lunar villages
- Allow for rapid transit to orbit (7.76 km/sec) routinely, safely, and robustly
- Allow fast transit of crews and payloads to Mars (minimum of 61 days to 400+ days)
- Allow missions to launch for Mars every day (not just every 26 months
- Enable the creation of space stations at GSA, Lagrange Points, and beyond
Some of these benefits are sure to sound familiar (and quite specific) for the astute observer of spaceflight and the commercial space sector. In short, a Space Elevator would help Elon Musk realize his vision of sending 1 million people to Mars between now and 2050, while Bezos could realize his dream of establishing habitats in orbit and at the Lagrange Points, leading to a civilization of "a trillion humans in the Solar System." Except that in this case, it would not involve thousands of rockets lifting small payloads to space, costing hundreds of billions (or trillions), and without the resulting damage to Earth.
Of course, a lot needs to happen to get us to that point, not the least of which is for the nations of the world and the commercial sector to invest in the idea. This is something that Nixon, Wright, and Knapman hope to encourage when they present at this year's International Astronomical Congress (IAC), which will take place in Paris from September 18th to 22nd. When asked what they hope to accomplish at the 2022 IAC, Nixon replied firmly:
"In a word, profile! Since the space community turned away from carbon nanotubes, they have not realized that 2D materials even exist. Those that are aware of graphene and hBN don't realize the astonishing progress being made in 2D materials manufacturing. We hope to spread the word with a well-researched paper, and we encourage as many people as possible to become interested in the space elevator again. The space elevator is not science fiction, it is closer to engineering fact. Could the space elevator be built in our lifetimes? Yes, of course, it just depends on how much serious effort is directed to this amazing technology."
It's an exciting time that we live in, where lower costs, more competition, and more cooperation are making space more accessible. In this age of greater activity and renewed interest, many time-honored concepts that were once considered unfeasible (or just too expensive) are being reevaluated. But when it comes to a cost-benefit analysis, few other ideas have the same potential as a Space Elevator. As always, many questions need to be addressed first to prevent additional challenges from arising in the future. But there's no shortage of dedicated individuals looking to tackle them!
Also, it feels appropriate to remind people that China announced that it was pursuing its own Space Elevator back in 2018, which it hopes to complete by 2045. Considering that the global space economy is worth $447 billion (based on 2020 figures) and shows no signs of slowing, other nations and commercial partners might want to get in on this project before long! If and when space becomes the most expansive and lucrative market there is, you don't want to be left out!