To Go Further Than Ever, We Need To Go Smaller Than Ever
By: Aahaan Maini
Tags: Nanotechnology, Space Elevator, Carbon Nanotube, Space Exploration, Space Travel

Since the beginning of time, we humans have always been explorers. From simple discoveries like fire to the transition from the stone age to the iron age to the age of technology today, everything was created by our need to explore. We need to challenge the norm.

We are built to grow, to dream big, to challenge everything around us. Only by exploring can we understand everything we are missing and work towards achieving it. We need to explore further. Farther. Smaller?

Now we are in a stage where exploring farther means outside our planet. We have already put a man on the moon, but why should we stop there? Why can’t we put more astronauts on the moon?

Dare I even say, on other planets like Mars? Is any of this even possible?

The answer 10 years ago would have been no. The answer today would be no as well. The predicted answer in 5 years is probably still a no.

Elon Musk’s aspirational timeline for SpaceX to put a human being on Mars is in 2025. He plans on using a truly massive (387 ft) rocket + booster combo and launching it to Mars. It's called Starship (previously BFR), click here to learn more about Elon’s plan for SpaceX and commercial spaceflight to Mars.

SpaceX Starship. Source

But all of that can change with the concept I am going to be explaining today. Turns out, nanotechnology is the key to making this a reality.

Before I get ahead of myself let's walk through why traditional rockets just aren’t cutting it.

Issues with Traditional Rockets

Chemical (traditional) rockets have been used to do some crazy things, including putting the first man on the moon, but we need to dream bigger.

The overall method that chemical rockets use is often referred to as the ‘brute force’ method because the oversimplified principle is to create a continuous explosion that generates enough thrust to break Earth’s gravitational pull and enter orbit.

Check out the chemical rockets section on the article below to dive deeper into exactly what are the issues with chemical rockets and why do they exist.

TLDR:

Method: Chemical rockets have to carry up all their fuel and oxygen for the combustion to occur, which is just added weight and cost

Efficiency: These rockets only have a fuel efficiency of 30% because of their combustion system. The specific impulse of a new chemical propulsion system can range from 300–500 SI (if you don’t know what specific impulse, read that section on the article above).

Cost: It costs around $20,000 to send 1 kg of cargo to space and each space shuttle launch can range from around $50– $400 million.

Size and Mass: For every bit of added mass, we need to carry more fuel and oxygen, which then in turn also increases the mass, which then requires more fuel and so on. This is called the Tyranny of the Rocket Equation.

What about other forms of propulsion?

For the last several decades, to solve the tyranny of the rocket equation, scientists have turned to other forms of propulsion.

Ion Engine. Source

Innovative methods that have been developed are nuclear propulsion, ion thrusters, solar sails, even something as crazy as antimatter propulsion (by the way, I cover each of these in detail in my other article here).

Nuclear Propulsion Rocket. Source

But these new forms of propulsion, don’t solve the initial problem of the rocket equation, they just tackle it from a slightly different angle. To completely change the approach, let's first understand how rockets get to different places in space.

How rockets reach orbit and beyond

The first step in getting rockets to orbit is breaking Earth’s gravitational pull. For this to happen, the spacecraft needs to be launched and maintain a speed of over 40,000 km/h!

Once it reaches its desired height, the rocket then rotates horizontally and enters the orbit around the Earth, all while maintaining its speed of over 40,000 km/h.

The way rockets and satellites stay in Earth’s orbit is by balancing their forward velocity with the gravitational force of the Earth and the curvature of the Earth.

Think about it like this. If you were to shoot a cannonball with its normal force, it would travel for a very little bit and then fall back down to Earth (Scenario A). If you increase the force to a very specific amount, the forward velocity of the cannonball will match the curvature of the Earth and instead of falling back down, it will enter Earth’s orbit (Scenario B). Lastly, if you increase the force too much, the forward velocity of the cannonball would just fly straight ahead (Scenario C.)

To calculate the specific velocity required, we use the following formula, where v is the orbital velocity, g is the gravitational constant, m is the mass of the planet and r is the radius of the orbit (distance from the rocket/satellite to the centre of the planet).

The purpose behind that explanation was to explain how traditional rockets use the orbits of Earth or other planets to propel them towards their destination to increase speed and save rocket fuel. This is called gravity assist.

Demonstration of Voyager 1 using Gravity Assist. Source

Now, what if we ignored the complicated trajectory calculations and just built a machine that takes us straight up, straight towards our destination. Sort of like an… elevator?

An elevator to… Space?

Precisely.

The space elevator is a concept that has been around since 1969 when Jerome Pearson conceived the concept at the NASA Ames Research Center.

The fundamental principle of a space elevator is an elevator with one end attached to Earth and the other end in space.

Diagram of a Space Elevator Concept. Source

To keep this article short and sweet and focus on the technical nanotechnology aspect, I highly recommend watching the Kurzgesagt video below which explains it beautifully.

TL;DR

The space elevator has 4 main parts:

Anchor: a material attaching the tether to the Earth Tether: a cable that extends thousands of kilometres into space, only bound to Earth by one end Counterweight: a weight on the space end of the tether with enough force to keep the tether held tight Climber: similar to a traditional elevator car, a machine that would travel up the tether and release the load

Almost there…well, not really

While space elevators have a variety of logistical issues mostly around the production and deployment of the mechanism, by far the most complicated challenge to overcome is the manufacturing of the tether. The tether must extend over 42,000 km into space while also being light, flexible, affordable and durable enough to withstand the harsh conditions of outer space. This includes dangers like radiation, space debris and asteroids.

However, scientists are optimistic that these smaller issues can be dealt with shortly, as long as the production of the tether is solved.

The material for the tether needs to have a tensile strength (force needed to pull apart) of at least 63 gigapascals (GPa) or 63,000 MPa, whereas steel has an ultimate tensile strength of 400–500 MPa. Not even remotely close to what is required.

Graph showing the stress-strain relationship of steel. Source

Nanotechnology to the rescue!

Right off the bat, scientists and researchers turned to “the wonder material”: graphene. More specifically, carbon nanotubes, which are just rolled up sheets of graphene.

Instead of finding a material 200 times stronger than steel to increase the tensile strength, we can turn to much less dense materials, which decreases the amount of tensile strength it will have to endure.

Single-crystal graphene has a tensile strength of 130 GPa (130,000 MPa). One of the many reasons it is the strongest material ever tested. Single-walled carbon nanotubes have a similar tensile strength of 100–200 GPa (100,000–200,000 MPa).

Single-crystal graphene (AKA crystalline) and other materials are when the formation of the crystals is even and structured throughout, without any grain boundaries (2D defects in polycrystalline materials in between sections of the material — signified by the gray lines).

Before we dive any deeper, I just want to clarify that graphene itself will not be used for the tether, neither will raw carbon nanotubes. Instead, scientists will develop a fibre made out of several layers of carbon nanotubes.

Carbon Nanotubes

Carbon nanotubes can be fabricated in 1 of 3 different configurations: Armchair (default), Zigzag and Chiral. The difference between each of them is in the orientation of the graphene when it is “rolled”.

Scientists tested over 16 different variations of the 3 configurations to come to the conclusion that the armchair configuration had the highest tensile strength of over 60 GPa. But that is not nearly what the production result is.

Depiction of the tensile strengths of the armchair configuration. Source

Due to the nature of carbon nanotubes, one single misaligned atom turns two of the congruent hexagons into a pentagon and a heptagon, decreases the ideal tensile strength from 100 GPa down to 40 GPa, which is unable to fulfill the role of the tether for the space elevator.

Structure of a carbon nanotube. Source

In other words, out of a potential 42,000 km long fibre of carbon nanotubes, not even a single misaligned atom is allowed. Every misaligned atom creates a week point in the tub, which snaps the normally extremely strong bonds between the atoms. This causes a chain reaction of the subsequent bonds to break as well.

Carbon nanotube manufacturing methods are either very expensive, time-consuming and produce very little quantity for very high-quality nanotubes. Due to mass fabrication methods being heavily flawed, using carbon nanotubes is currently not a viable option.

One method of carbon nanotube production. Source

You either choose quality or quantity for nanotubes and in our case, we need both.

While carbon nanotubes are definitely not the only nanomaterial which exhibits extraordinary properties, it is the only one that has been successfully produced with a tensile strength of over 100 GPa. The next best materials had tensile strengths of around 20 GPa, only 40% of the efficacy required for the tether.

The Kurzasagt video above mentioned another possible material, diamond nanothreads. Diamonds are actually made from carbon atoms as well, just arranged in a specific 3D lattice.

Diamond nanothreads are essentially 3D graphene. In standard graphene, each carbon atom is bonded extremely strongly to 3 other carbon atoms, constructing the 2D lattice. In the nanothreads, each carbon atom is bonded extremely strongly to 4 other carbon atoms, creating a 3D shape. Watch the video below to learn more.

These nanothreads have been proposed back in 2015 as a stronger, stiffer and more resilient upgrade of carbon nanotubes. However, the same obstacles occur. To start off, to the best of my knowledge, scientists haven’t even produced these diamond nanothreads yet but rather constructed it in molecular simulations. There is a long path ahead for the mass production of these diamond nanothreads, especially for space elevators. On top of that, the same issues with misaligned atoms and the efficacy of current fabrication techniques result in the possibility of using these turning into a pipe dream.

Is it possible? By when?

The production of the tether is only one of the many obstacles that space elevators including:

The deployment of the tether

Managing the forces of Earth and its rotation

The power source of the climber

Anchoring the tether to the Earth

Safety of the entire elevator and the passengers

Hundreds of thousands of smaller logistical problems

and of course, the price! Each scientist has developed their own variation concept of a space elevator, the optimal materials, the deployment technique and more, so each price estimate will be different. As of right now, the estimated cost to fully build and deploy a space elevator is between $8 billion and $90 billion! While that might seem like a lot, keep in mind that the cost of the International Space Station was $150 billion.

The Obayashi Corp in Tokyo has announced that it plans to build a fully functioning space elevator by 2050. Following that, China announced its goal to build one by 2045.