**What is a space elevator?**

A space elevator is an elevator that takes us out of the earth’s gravitational field or out of the earth’s atmosphere. The space elevator is simply an idea at present coming from the dreams of a person watching the open sky from earth and thinking what it would look like to see the earth from space. To make it feasible either we should be an astronaut or a billionaire out of which the most economical way for a normal human to see space is to build an elevator to outer space. We got an impossible dream to build a space elevator but since necessity is the mother of all inventions let us see its possibilities.

## What if we built a space elevator?

We could decrease the cost of shipping 1kg of weight from earth to space i.e., approximately 20,000 dollars to 200 dollars by using the space elevator. Based on this for an average weighted human to travel to space it would cost around 1.4 million dollars which is impossible for a normal human to afford. This is where the space elevator comes into the picture. It could decrease the whole expenditure by 100 times than its original price. Thus, a normal human can also afford to travel to space. This space elevator changes the face of a space expedition to a whole new level.

## Theory of a Space Elevator.

The elevator moves between two points i.e., the starting point and the stopping point. For a space elevator, the starting point is the earth and the endpoint should be some point in space.

Let us consider the conditions of the point in space where we can place the endpoint of the elevator.

- The endpoint should always be on top of the geographic location, where the space elevator is built.
- The endpoint should always stay at a constant distance away from the earth.

The best location in space for the endpoint of the space elevator is geostationary orbit because the point on the orbit stays on top of a location at the same time staying at a constant distance away from the earth’s core even when the earth revolves. Geostationary orbit is special because its orbit is circular due to the effect of counter forces acting on each other i.e., the earth’s gravitational force and the centrifugal forces.

For a satellite in geostationary orbit, the earth’s gravitational force and centrifugal force cancel each other.

From this equation, we have the distance between the center of the earth to the endpoint of the elevator i.e., is equal to 42,168 km. We could reduce this by taking the start point of the elevator on the surface of the earth at the equator now the distance between the space elevator start point and the endpoint is 36,000 km. So from this, We got some numbers to work with. But to build an elevator to space we are required to design its parts efficiently keeping those numbers in mind.

## Parts of a space elevator.

The main parts of the space elevator are

1. Anchor

2. Counterweight

3. Tether

4. Climber

### Anchor

Anchor or the base of the space elevator. Base or the foundation of the structure is the part of the structure where the compressive strength(entire weight) of the structure gets piled on. With the rise in height, the base width should also increase to counteract the weight or gravitational force take the examples of ancient marvel the pyramids of Giza to the modern marvel the Burj Khalifa all of them are broader at the bottom going to a pin tip at the top thus distributing the gravity across its base. So their structures could have integrity and stability to withstand the extreme conditions due to the structure’s height and weight. Now keep in mind these basics of construction for our space elevator spanning over 36,000 km in height what should be the base area? This will be an impossible task for us to build the base for our construction. Now since in our space elevator the other end goes to the geostationary point in the space we could place a counterweight at the endpoint of the space elevator in the geostationary orbit in space for counteracting against the earth’s gravitational force with its centrifugal force. With this, we could decrease its base area to a large extent.

### Counterweight

The weight acts against the earth’s gravitational force and keeps the tether or the line tight. This could be a satellite, monitoring station, or space station from which they could control everything about the space elevator.

### Tether

Tether is the material that connects the start point and endpoint of the space elevator. For a good tether for our space elevator, we should consider the following conditions.

- The tether should span over 36,000 km in length.

- The tether should withstand various temperature changes.

- The tether should withstand the tensile stress acting on it.

Tensile stress is calculated using this formula where we can only modify the density term based on the material taken. The remaining quantities are fixed quantities.

- The tether should be in the shape of a tapered tower because the stress is not uniform throughout the length of the tether.

- So the area of cross-section of the tether will be minimum at the start point and maximum at the endpoint depending on the material used for the construction of tether

The area of the cross-section of the tether at the endpoint is found using this formula where,

A is the area of the cross-section at the start point.

P is the density of the material chosen.

T is the tensile stress of the tether.

The remaining all other terms are constants in the equation

Keeping in mind the conditions above the following materials are taken into consideration for building tether

#### Materials for Tether

**1. Steel **

Steel is a widely used material in construction work because of its high tensile stress. But we cannot use it in building our space elevator because of its high density. Due to its high density, it has to withstand high Tensile stress i.e., 382GPa which is 282 times more than the ultimate tensile strength of the steel, so it cannot be used.

**2. Kevlar**

Kevlar is a synthetic fiber used in many applications due to its tensile strength being more than that of steel but having less density. This is a feasible material that can be taken into consideration for making tether. But the radius of the cross-section at the endpoint for Kevlar choosing that it has 5millimeter at the start point would have an 80-meter radius which is not possible to build.

**3.Carbon Nanotubes**

This would be the answer for the tether construction because carbon nanotube has the highest tensile strength with the lowest density. The area of the cross-section at the start being 5millimeter and the area of the cross-section at the end is 1.2 meters which are feasible to build. For now, carbon nanotubes are the material for tether.

But the problem arises when we need to mass-produce the material required for a 36,000 km long tether. Let us leave this for our scientists and engineers to discover.

### Climber

The climber is the part of the space elevator that climbs up and down the tether. The climber can be built using any material capable of holding air pressure in a Vacuum. But the major problem is, How to power the climber?. For a normal elevator, we use diesel engines or electric engines to power the elevator. This is enough to power it up but for the climber to get away from the earth’s gravitational field high energy is required. Whether to use a nuclear reactor or other high-energy producing sources to power the climber. There are no theoretical concepts on how to make the climber and power it till now. This gives future researchers a research idea to work

## What if?

### What if the tether breaks at the endpoint?

Then the space station which is the counterweight for the space elevator gets thrown away from its orbit. The tether falls back wrapping around the earth. This will have a serious impact on earth rotation and revolution.

### What if the tether breaks at the start point?

Then the whole tether and counterweight rise up and away from the earth.

So that is why we are not trying to build the space elevator on earth, keeping all the possible negative effects. But the scientists are proposing to build an elevator on the moon to check the feasibility of a space elevator. This will be on another article let's leave this topic for now.

## Elon Musk-Space Elevator

**Should we leave the dream of a space elevator - Elon Musk?**

Elon Musk the founder, CEO of SPACE X (Private Space Exploration Company) and TESLA. He said that this idea is too far-fetched in a conference at MIT. He said that it is not realistic to have a space elevator. With the tech now we are not able to build a bridge between LA to Tokyo of 3000 miles using carbon nanotubes how can we build a space elevator spanning over 30000 miles. But at last, he said that in the future it may be possible.

Since we are the future Let us hope to see the space elevator by the time we die. Space Elevator, for now, maybe a theoretical concept but in the future, let’s hope that it comes into reality.

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