Adrian Nixon, CEO of Nixor Limited, will be answering questions on this topic at the Global Graphene Expo, October 15-17.
How does a space elevator work?
The concept is straightforward. At the moment the only way of getting into space is to ride on a rocket. However, there is another way.
Imagine you are standing at the equator. A geostationary satellite has been launched into orbit right above you. From your point of view, that satellite will always be directly above you.
Now, imagine that you could drop a cable from the satellite down to the ground. You would see the cable directly in front of you. You could grip the cable, start climbing and eventually, you would climb all the way up into space. That’s it.
Even though the concept is straightforward, actually doing it is quite the opposite. It will be one of the major engineering challenges of all time, but graphene could help.
It sounds like science fiction! Could a space elevator really be built?
When I first heard about the space elevator I thought it was science fiction too. Then I looked into the background and I discovered there is a worldwide community of very credible engineers and rocket scientists who believe this can be done and they are actively working on the technology.
Back at the turn of this century, NASA decided to find out whether this was a realistic project. The NASA Institute for Advanced Concepts (NIAC) funded a feasibility study into the Space Elevator, using one of their most respected scientists, Bradley C. Edwards. Dr. Edwards conducted a thorough six-month investigation and reported back with findings based on an assessment of the challenges involved and the key components of the technology:
There are four basic elements of a space elevator.
- The base station and anchor.
- The counterweight and orbital space station.
- The tether (the cable that connects the surface to space).
- The climber (the elevator carriage).
Dr. Edwards found that given enough money and time, everything apart from the tether could be created with the current technology. There was no material strong enough to make the tether. Carbon nanotubes were proposed as a candidate material but no continuous production process has emerged that can make them in the quantity and quality needed.
So, the whole space elevator project effectively stalled. However, a global group of highly skilled rocket scientists and engineers kept alive the idea in an organisation called the International Space Elevator Consortium (ISEC). They maintain a constant watch on developing materials science.
Since the NASA report was commissioned, a new material has been isolated – graphene. The technology of graphene is maturing and it now has the attention of ISEC as a candidate tether material.
What are the main challenges making Graphene materials for Space Elevator tethers?
Graphene is a fantastic 2D material. It is 200 times stronger than steel, transparent, flexible and conducts electricity better than copper. However, graphene can only be made commercially in little bits with the current technology.
Take for example, the ‘200 times stronger than steel’ property. You can’t make full use of that at the moment because the current commercial state is to produce graphene from graphite using the top-down method. This makes graphene as nano plates that are typically 400 nanometers long. To give an idea of how small this, look at the edge of a piece of copier paper, which is 100 microns (100,000 nanometers) thick. You could fit 250 of these graphene nanoplates across the edge of that piece of paper.
So, you can see graphene nanoplates really small. You can imagine that if you wanted to use the current commercially available graphene for a space elevator task, and lots of other applications, you’re going to need something like a chain. You’ve got all these really strong small links, but they’re not connected together so nanoplate graphene will not work.
The first solution you might consider would be to glue together the nanoplates. Research has been carried out looking at copolymerizing graphene nanoplatelets with various polymers to make a strong composite, however, this is not strong enough to be a viable tether material.
The other way of making graphene is by the bottom-up method, which assembles graphene, atom by atom. The leading technology is called Chemical Vapour Deposition (CVD). Even though this process is really still in its infancy from an industrial point of view, it is impressive.
The CVD process usually involves heating methane and hydrogen to just below 1000 degrees centigrade over a clean metal surface, such as copper or nickel. As the hot methane approaches the surface of the metal, a reaction takes place catalyzed by the metal that removes the hydrogen from the carbon in the methane molecule. The carbon from the methane lands on the metal surface and starts to link up with other carbon atoms. The lowest energy structure is a flat sp2 hybridized carbon – in other words, graphene. Once the surface is covered, the reaction stops, leaving a one atom thick 2D covering of graphene on the metal.
You would think you would have a continuous sheet of graphene across the surface, but you don’t get a perfect layer because there are some problems. One, is that the surface of the metal contains cracks at the microscopic level, (it looks a bit like crazy paving). When the graphene layer grows over that, it often picks up these discontinuities and you will get defects in the sheet.
Another problem is that graphene grows from multiple spots at the same time; a bit like snowflakes landing on a pavement. These form separate domains, which gradually increase and then butt up against one another. Again, you get discontinuities. This creates polycrystalline graphene.
Having made the graphene layer, you now have to remove it from the metal. There are two basic approaches. The first is to dissolve away the metal using an etchant solution such as a strong acid or oxidizing agent. The second is to use a strong sticky tape. The sticky tape method usually leaves a polymer residue that contaminates the graphene.
Both methods are currently a batch process, although teams in the UK, USA and Norway are working on turning this method into a continuous process. All of these methods are still in the laboratory phase at present.
How can you make Graphene suitable for space elevator tethers?
The tether needs to be as strong as possible, so this means the entire length of the structure needs to be made from single sheets of graphene that are defect free. Such a structure would be a single molecule at a macro scale. Until recently this was thought to be impossible
However, back in January and March 2017, I proposed a continuous process for making defect free sheet graphene in rolls.
Things then started to get really interesting, because later that year (in the summer of 2017) a team at Peking University announced they were the first to make near perfect graphene at a scale of 500mm x 50mm. They called this material single crystal graphene. A crystal in this context refers to a repeating regular pattern, rather than the sparkling brittle crystals of our everyday experience.
Single-crystal graphene is important because it is very strong. Tensile strength is a measure of the force needed to pull apart any material and is measured in Pascals (Pa). Commercially available structural steel has strength of 550 MPa (550 Million Pa). A space elevator tether needs to be made from a material with strength of at least 50GPa (50000 MPa), so steel is not strong enough. Single-crystal graphene on the other hand, has a tensile strength of 130GPa. (130000 MPa). It is the strongest material ever tested and will be strong enough to make a space elevator tether.
To answer your question, single-crystal graphene is the material that can make space elevator tethers. That material exists. It has already been made in the laboratory.
As nothing like a space elevator has ever been made, how much can you theoretically and practically test it?
NASA has done a great deal of the theoretical work on the elements of the space elevator. The International Space Elevator Consortium (ISEC) and others have continued this work so we know where the space elevator could be built and many of the obvious technical challenges have been thought through and addressed.
As far as single crystal graphene is concerned we are still at the early stages. We know the material has been made at a laboratory scale but samples have been isolated for further testing.
A few weeks ago, in May 2018, a team in South Korea made near perfect single-crystal graphene at the centimetre scale for testing in a laboratory. They measured the strength directly and found that the sample had a Young’s modulus of 0.9 TPa. This is very close to the predicted value of 1.0 TPa and establishes graphene as the strongest material ever tested.
If you want to find out more, I’ll be presenting about this and more at the ISEC conference in Seattle on the 17th August 2018.
How close are we to constructing the real thing?
The space elevator is about to enter the public consciousness; in simulation anyway. Disney announced a few days ago that they are now working on a Space Elevator simulator to an orbital restaurant at Disney World’s Epcot Centre in Florida!
Arthur C. Clarke famously said the space elevator would be built fifty years after everyone stopped laughing. The laughter has already stopped. The real thing could be closer than you might think. A proof of concept project will be necessary to show that single-crystal graphene can be made by a continuous process. Then a series of follow up projects to design and make the production machines, so that the process can be optimised and scaled up properly. The ISEC team estimates it will probably take about 20 years. It will cost approximately 20 billion dollars just for the tether.
To actually build all of the other elements, it would probably cost another $80 billion. We could get it to completion for somewhere under 100 billion dollars, over a 20 to 30 year period. That figure compares with the global space industry that is worth around 360 billion dollars in 2018 alone.
You probably would discover all sorts of interesting things going forward as well, because the ROI on all this is just staggering. It might even happen in my lifetime, however there are still many hurdles to overcome.
I wouldn’t want to give anybody the impression that it’s going to happen anytime soon. At the moment this is a set of ideas – they’ve been well thought through, but they need testing properly. This will be an industrial strength challenge over an extended period of time but I’m convinced this can be done.
How will the space elevator benefit us, and what do space elevators mean for the future of space travel?
Apart from getting us into space smoothly and safely, the operating costs are low. At the time of writing you can expect to pay around $20,000 per kilogram to take a payload into orbit, but with the space elevator, once you’ve paid all the setup costs, then you are down to $100 or $200 per kilogram. Even with large set up costs the business case is compelling.
It makes a lot of sense with the return on investment (ROI) over a long period of time. If you’re just going to use it as a one off, then it’s a very expensive onetime thing, but the idea is that once you get a space elevator built space travel becomes routine and cheap.
Dr. Edwards summed up the implications in his report for NASA: “…the long-term return we (humans) would receive on the construction of a space elevator is staggering, it would literally change our world.”
AzoNetwork is a media partner with NGA.
Interview conducted by Zoe Peterkin
Zoe is an Advisory Board Member of NGA
Join us at Global Graphene Expo & Conference, Oct 15-17, Austin, TX