Space elevators: ‘Stairway to Heaven, Bridge to the Stars’

Arthur C. Clarke's 1980’s classic novel, ‘The Fountains of Paradise’, envisages a world where conventional fuel-powered rockets are replaced by an ‘orbital tower’. At a fraction of the cost of a rocket, a space elevator consists of a 22,000 mile-long ribbon attaching a satellite in geosynchronous orbit to a platform on Earth. This idea has been treated as science fiction by many physicists, but EUSci talked to a NASA researcher, and ’driving force’ behind space elevators, Dr Bradley C. Edwards, who believes that carbon nanotubes offer sufficient strength to make this dream feasible.

To understand the concept of space elevators, imagine swinging a weight at the end of a string around your head. Centrifugal force would keep the string rigid. The technical challenge is designing a string rigid enough to allow an elevator to travel up and down. Carbon nanotubes may be the answer. They are a recently discovered formation of carbon molecule, which could give the 22,000 mile-long ribbon enough strength to withstand up to a 13 ton payload. This makes carbon nanotubes 100 times stronger than steel.

Carbon nanotubes were discovered in 1991 by Professor Sumio Iijima. He found that common hydrocarbon molecules could be transformed into tubular molecules by passing a current of 50A between two graphite electrodes in an atmosphere of helium. The original molecules would vaporise and condensation on the walls of the reaction vessels would produce the nanotube. At a few nanometres in diameter, it is approximately 51,000 times smaller than the width of a human hair and its properties are unparalleled in material science.

However, the sheer complexity of engineering the space elevator leads many sceptics to believe that the idea is no more than a dream for sci-fi romantics. The idea is to launch a spacecraft into low Earth orbit and then use a propulsion system to raise it above geosynchronous orbit. From there, a three foot wide, and thinner than a paper ribbon, carbon nanotube would be deployed back down to Earth. The anchor platform could be somewhere in the eastern equatorial Pacific.

Sceptics also argue that the risk of unpredictable Pacific weather means that the elevator is too dependent on seasonal climate trends, far more than a rocket. NASA would also need to clear the Earth’s orbit of debris to ensure the ribbon could not be damaged. One idea would be to create NASA’s very own ‘space garbage trucks’, which would need to clear the 3,000 identified objects over 2 kilograms floating in orbit to allow the space elevator to operate.

The elevator could be powered via electron laser beams on the ground firing at photovoltaic cells on the vehicle, in a process called ‘power beaming’. This is a form of wireless power transmission and could mean the end of expensive, environmentally unfriendly rocket fuel. It has also been proposed that the elevator could be powered through the ribbon itself. However, though some types of carbon nanotubes have high conductivity, sceptics argue that the distances involved make electrical transmission impractical.

Many sci-fi enthusiasts have placed their hopes in the space elevator as the only realistic way to transport the general population to space – whether it’s for a holiday on the moon, or the creation of franchise cities in space. The space elevator could also solve one of humanity's biggest challenges; what to do when Earth is no longer inhabitable. This is a pressing question; the likes of Professor Stephen Hawking are warning that the human race needs to expand into space due to the impending effects of global warming.

Dr Edwards told EUSci that, “The elevator is the only means for man to move into space in a real way”. With each rocket launch costing NASA half a billion dollars Dr Edwards argues, “Rockets are too expensive and limited in their capabilities for colonization or large-scale utilization of space”.

Scientific consensus is that humanity should prepare for the consequences of global warming and perhaps look for a new home. Dr Edwards warns that, “Depending on what happens in the next decades, getting into space may be critical.”

It is humankind’s willingness to explore and define the impossible that will be the real catalyst for reaching the stars. Carbon nanotubes provide the strength to make this dream possible, but further research into untested technology and scientific will are desperately needed to convert possibility into reality.