What do you think of space elevators?

Compiled by Aravinda Dassanayake

Jack's beanstalk becoming a reality?

Just recall the famous story of 'Jack and the beanstalk' which fascinated you all when you were wee little kids. In this particular story, the beanstalk grew so tall that it went past the clouds and touched the giant's land and Jack used this as a ladder to go up to that land.

The same concept has been taken into consideration by the space scientists to transport material into outer space. Let's find out in simple terms what this complex concept means.

Humans are no longer restricted to living on Earth. Efforts are being made to move into outer space and colonise other planets or at least study other planets. In this effort, transporting various materials in to outer space is necessary, and it is not at all a cheap process.

Rockets have been used ever since the dawn of space travel and it costs millions of dollars for one rocket trip.

Under the concept of space elevators, rockets are going to be replaced by the construction of a particular structure which is quite similar to the elevator that you see in modern buildings.

Space elevators are also referred to as space bridges, space ladders, space lifts and of course beanstalks too.

Challenges

This may seem like a very simple design. But, think about the magnitude of the project. It's not going to be easy. The major requirement is that the material used in the 'tether' or the cable should be lightweight, but strong enough to withstand the tremendous stress.

Remember that this is a cable which is quite thick, and its length is going to be thousands of kilometres. Up to now, no material with such qualities has been discovered.

But, the latest discoveries in carbon nanotubes which is a new structure of carbon, apart from diamond and graphite, is showing some signs of making the material requirement a reality to a certain extent.

Apart from that, corrosion of the cable is going to be vital and things like lightning and defects in the cable can have bad effects. Since the cable runs in to outer space, meteorites may collide on the elevator as well.

However, under the requirement of so many new technologies, it is believed that the first space elevator will be in operation by 2031. Keep that in mind since you will be able to witness this achievement.

Construction

Let's consider how the space elevator is constructed. In fact, there are several proposals to make this a reality. But, the design which seems much more practicable and economical is called the 'tether'.

The idea in this design is to use a long cable which would span from a point on Earth in to outer space which would be to a point past the geostationary orbit, and the centre of gravity of the entire cable shall be on the geostationary orbit.

For your information, the geostationary orbit is the orbit where if a satellite is placed, it would take twenty four hours to go around the Earth once. That means, in this situation, it is as if the satellite's position is fixed relative to some point on Earth since the Earth too takes twenty four hours to revolve around its axis.

Then, the gravitational pull on the cable by the Earth will be cancelled out by the inertia (resistance to change) at the other end, and this will make the cable to be rigid.

Once the cable is rigid, that can be used as a support for various vehicles to travel along it to transport materials, and it is going to cost just a fraction of the cost of a rocket launch.

The important parts of this assembly are the base station and the cable. The base station is the end where the cable is fixed to Earth. This may be mounted on a large ship or fixed to the Earth permanently.

If the mobile method is used for the base station, it can avoid high winds and storms. However, having a fixed base station is going to be less costly. Where the cable is concerned, it must have a very high tensile strength/density ratio.

Tensile strength is the maximum stress that can be applied on the cable without breaking and density, as you may know is the mass of unit volume. Although we use metals to make cables for domestic activities, metals are not suited for the cable of the space elevator since it has comparatively low tensile strength.

Consider the following figures just for comparison. The required tensile strength for the space elevator is 60-125 GPa (Giga Pascals). But, the tensile strength of steel can go up to just 5.5 GPa. Just understand that Pascals are used to measure tensile strength and 'Giga' is a prefix used to imply 109.