Towers of Strength

Arthur C Clarke: Fountains of Paradise

An easier approach to space travel – in the long run. Published by Pan Books 1980. Cover art by Chris Moore.

Space elevators would significantly change the way humanity ventures into space.  The idea is that a tower could extend from the Earth’s surface to a structure in geosynchronous orbit, which might one day even become an orbital ring around the planet.  Such a permanent facility would enable people and cargo to be transported upwards via an elevator to a location from which they could then be propelled into space without all the immense cost of having to launch a spacecraft from the ground.

But there are major problems in building such a wonderful construction, even apart from the huge expenditure required – not least creating materials of sufficient strength to provide the tethers or cables of such colossal length that could have a centre of mass at geosynchronous orbit, which is over 22,000 miles high.  That requires exceptionally strong materials, and it has long been known that this factor alone could become something of a show-stopper.  They don’t exist at present.

Arthur C Clarke’s 1979 Hugo and Nebula award-winning novel The Fountains of Paradise is often regarded as a seminal science fiction work on the subject.  In the twenty-second century, the technology has been developed to construct an “orbital tower” rising from an island in the Indian Ocean, though there are numerous setbacks before the project achieves its eventual success.

Clarke describes the concept of a space elevator built from a material called “hyperfilament”, which was to be a form of continuous diamond crystal.  At the time of writing, this was a reasonable conjecture, though Clarke later suggested that the forms of carbon known as fullerenes – large molecules where atoms are linked as hollow spheres or tubes – might be strong enough for space elevators in reality.  Even so, it was widely recognised that creating them would be far from easy.

Paul Birch considered the problem in Orbital Ring Systems and Jacob’s Ladders II (JBIS, March 1983).  He suggested that an alternative approach of a massive orbital ring in Low Earth Orbit – considerably lower than geosynchronous orbit – with “skyhooks” that ride on the ring and maintain station above specific points on the Earth’s surface and from which cables (known as “Jacob’s Ladders”) descend to the ground, could feasibly be engineered with today’s technology.  Clearly, an elevator that does not need to get anywhere near as high as geosynchronous orbit would not need to be so strong, but would still be quite a challenge.  And, in any event, developing strong enough materials to provide the cables that would enable a space station at the full height envisaged by Clarke and others to be connected to the Earth would still be a very attractive prospect.

In Advances in High Tensile Strength Materials for Space Elevator Applications (JBIS, June 2016), Mark R Haase, who also spoke on the subject at the BIS Space Elevator Symposium in November 2017, explained that there is no currently available material that would fit the bill, but some nanomaterials show great potential.  Carbon nanotubes and boron nitride nanotubes are strong enough at the molecular level, but such properties have not been expanded to a larger scale.

However, he believes that carbon nanotubes which meet the strength requirements could be produced within the foreseeable future.  And in Going up? (New Scientist, 12 January 2019), Kelly Oakes puts them at the top of the list of possible candidates, along with graphene – a two-dimensional lattice of carbon atoms which has already been grown as single crystals up to 30cm long.  But practical scaling up of this material still has a long way to go.  Even so, she adds that a Japanese company is aiming to develop a space elevator by 2050, and China even earlier by 2045.

It may yet happen, though facilities to launch spacecraft from the far end might take a bit longer.

 

 


Richard Hayes, Assistant Editor (Odyssey)

With a lifetime’s interest in science, history and human behaviour, Richard Hayes focuses his writing on how the imagination has created the world in which we live, and where it may lead us in the future.  Odyssey, the e-magazine of the British Interplanetary Society, draws on the rich treasury of science fiction to explore many fields of speculation, enabling us to glimpse what might yet be, both here on Earth and out amongst the stars.

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