Thanks to Jos Walker for suggesting this topic. In 1895 the Eiffel Tower, a technological marvel of its time, inspired Konstantin Tsiolkovsky to ponder what would happen if it had been built tall enough to reach in to space. He suggested a height of 35 790 kilometres, and that a ‘celestial castle’ be built at the top. This castle, obviously, would constantly remain over the same spot on the surface – a geostationary orbit. The idea was ahead of the materials science of the day, as no substance existed which would be able to support its own weight in such a massive structure. In 1959, as the space race began, it was another Russian scientist, Yuri Artsutanov, who suggested a variation on the idea. His idea was to have a satellite which would lower a cable to the surface of the earth, whilst at the same time deploying a counter-weight on a cable in to a higher orbit. He also proposed tapering the cable thickness so that the tension in the cable was constant—this gives a thin cable at ground level, thickening up towards geostationary orbit.
In 1965 four American physicists proposed a very similar idea in the journal Nature, but even then it was decided that no substance existed which would be strong enough to build the required cable of over 35 000 kilometres. It was not until the development of carbon nanotubes in the 1990s that materials science was able to support the concept, which could become a reality in the 21st century. It has been suggested that the establishment of a prize, along the lines of the Asari X-prize, may speed up development. As recently as 2008 a book, titled “Leaving the Planet by Space Elevator”, was published in Japanese and became a best-seller in Japan. As a result the Japanese government have committed to building a space-elevator at an estimated cost of some £5 billion.
In a conventional elevator the car is raised by pulling on cables. The space elevator would use a cable that would remain stationary, and the elevator would ‘climb’ up the cable. Several power sources have been suggested, but the emerging favourite is to use a megawatt laser in conjunction with 10m wide mirrors at various heights on the cable. If the counterwight was at a distance of 144 000 Km,then ‘firing’ a vessel from that distance would impart enough velocity to escape Earth’s gravitational pull. The concept is very much in vogue, and Nasa are considering the viability of a space elevator, and even building one on Mars to aid the colonisation of the planet.