Space Elevator Tether Materials:
The Crux of the Matter

Nobel prize winning discovery unlocks the potential of the Space Elevator

The Space Elevator

The basic concept of a Space Elevator is to launch a satellite into geosynchronous orbit, lower a tether down to the surface of the Earth, and then climb up the tether into space. All of the parts of a Space Elevator can be done with today’s technology apart from one element – the tether, which requires a material strong and light enough to support its own weight plus that of the payload. The tether would be 100,000 kilometers long and 1 meter wide with the thickness of plastic wrap (e.g. Saran Wrap). Until recently the only candidate material was carbon nanotubes, but manufacturing this material in the quantities needed has proved a challenge unmet.

Three Tether Material Options

Today there are three known materials strong enough for a space elevator: carbon nanotubes, hexagonal boron nitride, and single crystal graphene. Single crystal graphene is currently the most promising. These three materials are illustrated in the diagram below.

candidate tether materials

The Nobel Prize Discovery: Graphene

In 2010 two scientists at the University of Manchester, UK won the Nobel prize for discovering and isolating a new material called graphene. Graphene is a new form of carbon 200 times stronger than steel yet flexible and transparent. It is the world’s best conductor of heat and electricity. It has the highest melting point of any known material and is non-toxic. Graphene is strong enough and light enough to make the Space Elevator tether.

size and weight of graphene roll

Forms of Graphene

There are three important forms of graphene: Graphene Powder, Single Crystal Graphene, and Polycrystalline Graphene. Single Crystal Graphene is the form that will ultimately manufacture the Space Elevator tether.

1. Graphene Powder

Graphene is starting to revolutionize manufacturing. It is currently made in powder form and the Ford Motor company is already making quieter, stronger cars in the USA. For example, the 2019 Ford Mustang was graphene enhanced. Graphene powder has been added to asphalt roads in Italy where it doubles the service life of the highway. However, graphene powder cannot be used to make the Space Elevator tether.

2. Single Crystal Graphene

Single crystal graphene is the term used to describe a large-scale sheet of graphene with no defects. Making this material as a single molecule of carbon at the macro scale was thought impossible until the Chinese made this in the laboratory in July 2017. Since then other laboratories in China, South Korea and the USA have made single crystal graphene, producing half meter long single crystals with tensile strengths that could support the Space Elevator.

3. Polycrystalline Graphene

Polycrystalline graphene is composed of single-crystalline grains of varying orientation joined by grain boundaries. Defects can also take the form of vacancies where one or more carbon atoms are missing.

Industrial Manufacturing of Graphene

To make the material for the Space Elevator tether requires manufacturing on very large scales and speeds. Carbon nanotubes can currently be made at sub-meter lengths, very slowly. If a nanotube could be made a meter long, it would take 11 days. Graphene on the other hand, in its polycrystalline form, can already be made at lengths of one kilometer and a speed of 2 meters per minute. Neither material can be made at tether quality yet, but the trajectory clearly favors graphene as the industrial material of choice. There are at least four competing industrial companies manufacturing graphene at present.

Graphene Laminate

When graphene layers are formed without contaminants present each atomic layer can engage with the others. An electrostatic attraction called the Van der Waals force helps bond the layers together, creating a much stronger structure than would otherwise be expected. This bonding strength increases the rigidity with the cube of the number of layers. Also, a Van der Waals homostructure of single crystal graphene will be much stronger than one made from polycrystalline graphene.

graphene laminate

In 2021 the U.S. company General Graphene supplied ISEC with samples of layered polycrystalline graphene ranging from one atom thick to 30 atoms thick. A Space Elevator tether would be about 12,000 atoms thick at its thickest point.

Graphene Layer Bonding

The Van der Waals bond between the layers is much weaker than the covalent bond between the atoms within each layer. The ISEC climber-tether interface study group discovered that the Van der Waals bond between layers of graphene super-laminate is about 35 times too weak to support a 20-tonne climber without causing slippage between the layers.

A potential solution has been found in the literature. When two such layers are pressed together with sufficient force it can create a stronger bond called an sp3 hybrid bond, which is like that found in diamond which accounts for the diamond’s great strength. Using pressure to create such cross-links between the layers would in effect "spot weld" the tether and improve its resistance to slipping under shear. This bonding between layers is shown in the graphic below.

bonding between graphine layers

The Elon Musk Challenge

Elon Musk, well known for cutting to the chase, had this to say in a tweet about Space Elevators in 2015:

Please don't ask me about space elevators until someone at least builds a carbon nanotube structure longer than a footbridge

This was written before single crystal graphene was developed in the laboratory, and we assume he would accept a single crystal graphene structure longer than a footbridge as well. The longest footbridge in the world is Sky Bridge in the Czech Republic which opened in May 2022 and is 721 meters in length. A photo is below.

Sky Bridge, Czech Republic

Photo by Tomas Drapal, presented here and modified (cropped) under its Creative Commons license.

Polycrystalline graphene has already exceeded that length. We anticipate the day when this is matched by single crystal graphene and we plan to have a good conversation with Mr. Musk at that time. We have a small pool on when that might occur.

Latest information about Tether Materials from the ISEC Newsletter

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