An orbital ring is a concept for a space elevator that consists of an artificial ring placed around the Earth that rotates at an angular rate that is faster than the rotation of the Earth, but that has fixed tethers hanging down to the ground.
The structure is intended to be used for very high speed transportation and space launch.
|This section requires expansion. (August 2009)|
In the 1870s Nikola Tesla, while recovering from malaria, conceived a number of inventions including a ring around the equator, although he did not include detailed calculations. As recounted in his autobiography My Inventions (1919):
"Another one of my projects was to construct a ring around the equator which would, of course, float freely and could be arrested in its spinning motion by reactionary forces, thus enabling travel at a rate of about one thousand miles an hour, impracticable by rail. The reader will smile. The plan was difficult of execution, I will admit, but not nearly so bad as that of a well-known New York professor, who wanted to pump the air from the torrid to the temperate zones, entirely forgetful of the fact that the Lord had provided a gigantic machine for this very purpose."
Arthur C. Clarke's novel The Fountains of Paradise (1979) is about space elevators, but an appendix mentions the idea of launching objects off the Earth using a structure based on mass drivers. The idea apparently did not work, but this inspired further research.
A simple unsupported hoop about a planet is unstable. The orbital ring concept requires cables to the surface to stabilize it, with the outward centrifugal force providing tension on the cables, and the tethers stabilizing the ring.
In the simplest design of an orbital ring system, a rotating cable or possibly an Inflatable space structure is placed in a low Earth orbit above the equator, rotating at faster than orbital speed. Not in orbit, but riding on this ring, supported electromagnetically on superconducting magnets, are ring stations that stay in one place above some designated point on Earth. Hanging down from these ring stations are short space elevators made from cables with high tensile strength to mass ratio materials.
Although this simple model would work best above the equator, Paul Birch calculated that since the ring station can be used to accelerate the orbital ring eastwards as well as hold the tether, it is therefore possible to deliberately cause the orbital ring to precess around the Earth instead of staying fixed in space while the Earth rotates beneath it. By precessing the ring once every 24 hours, the Orbital Ring will hover above any meridian selected on the surface of the Earth. The cables which dangle from the ring are now geostationary without having to reach geostationary altitude or without having to be placed into the equatorial plane. This means that using the Orbital Ring concept, one or many pairs of Stations 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 of 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.
If built by launching the necessary materials from Earth, the cost for the system estimated by Birch in 1980s money was around $31 trillion if launched using Shuttle-derived hardware, whereas it could fall to $15 billion with bootstrapping, assuming a large orbital manufacturing facility is available to provide the initial 18,000 tonnes of steel, aluminium, 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
The manga Battle Angel Alita prominently features a slightly deteriorated orbital ring.
In the movie Starship Troopers, an orbital ring is shown encircling the Moon.
The anime Mobile Suit Gundam 00 also prominently features an orbital ring, which consists primarily of linked solar panels. The ring is connected to earth via three space elevators. This ring effectively provides near unlimited power to earth. Later in the series the ring also shows space stations mounted on its surface.
Arthur C. Clarke’s 3001: The Final Odyssey features an orbital ring held aloft by four enormous inhabitable towers (assumed successors to space elevators) at the Equator.
- Launch loop
- Megascale engineering
- Non-rocket spacelaunch
- Space elevator
- Space fountain
- Space tether
- Paul Birch, "Orbital Ring Systems and Jacob's Ladders - I," Journal of the British Interplanetary Society, Vol. 35, 1982, pp. 475-497. (see pdf (accessed 6 April 2016).
- Paul Birch, "Orbital Ring Systems and Jacob's Ladders - II," Journal of the British Interplanetary Society, Vol. 36, 1982, 115. (pdf)
- Paul Birch, "Orbital Ring Systems and Jacob's Ladders - III," Journal of the British Interplanetary Society, Vol. 36, 1982, 231. (pdf)
- Nikola Tesla, My Inventions, part III: My Later Endeavors (The gigantic machine he is referring to is better known as "air convection" and "weather")
- Техника-молодежи» 1982 №6, с.34-36 -"Technical Youth" 1982 - http://yunitskiy.com/author/1982/1982_02.pdf (Russian)
- Colin McInnes, "Nonlinear Dynamics of Ringworld Systems", J. British Interplanetary Soc., Vol. 56 (2003). (Accessed 6 April 2016)
- Carl A. Brannen, "Niven Ring Gravitational Stability" (Accessed 6 April 2016)
- "Orbital Ring Systems and Jacob's Ladders - I-III" (dead link)
- Paul Birch, "Supramundane Planets", Journal of the British interplanetary Society, Vol. 44, 1991, 169.
- Space Fountains and Orbital Rings
Media related to Orbital ring at Wikimedia Commons