can be positioned above any points on Earth desired, or can be moved everywhere on the globe. Thus, any point on Earth can be served by a space elevator. Also, a whole network of orbital rings can be built, which, by crossing over the poles, could cover the whole planet and be capable of taking over most freight and passenger transport. By an array of elevators and several geostationary ring stations, asteroid or Moon material can be received and gently put down where land fills are needed. The electric energy generated in the process would pay for the system expansion and ultimately could pave the way for a solar-system-wide terraforming and astroengineering activity on a sound economical basis. Estimated cost If built by launching the necessary materials from Earth, the cost for the system estimated by Birch in 1980s money was around $31 billion (for a "bootstrap" system intended to expand to 1000 times its initial size over the following year, which would otherwise cost 31 trillion dollars) if launched using Shuttle-derived hardware, whereas it could fall to $15 billion with space-based manufacturing, assuming a large orbital manufacturing facility is available to provide the initial 180,000 tons of steel, aluminum, and slag at a low cost, and even lower with orbital rings around the Moon. The system's cost per kilogram to place payloads in orbit would be around $0.05. Types of orbital rings The simplest type would be a circular orbital ring in LEO. Two other types were also defined by Paul Birch: Eccentric orbital ring systems – these are rings that are in the form of a closed shape with varying altitude Partial orbital ring systems – this is essentially a launch loop In addition, he proposed the concept of "supramundane worlds" such as supra-Jovian and supra-stellar "planets". These are artificial planets that would be supported by a grid of orbital rings that would be positioned above a planet, supergiant or even a star. Orbital rings in fiction Print In the close of Arthur C. Clarke's Fountains of Paradise (1979), a reference is made to an orbital ring that is attached in the distant future to the space elevator that is the basis of the novel. Arthur C. Clarke's 3001: The Final Odyssey (1997) features an orbital ring held aloft by four enormous inhabitable towers (assumed successors to space elevators) at the Equator. The manga Battle Angel Alita (1990-1995)