no further working once in space. It also does not have to be a complete ring; depending on the desired lifting power the total mass of objects might be much smaller than even the thinnest cable circling Earth. The main disadvantage is that the process of momentum exchange randomizes their velocity so some other system is required to shepherd the objects back into the correct orbits. History A detailed description of the concept was proposed and analyzed by Paul Birch in 1982, proposing a massive ring that would encircle the globe in low orbit, from which cables hang down to Earth's surface. In 1982, Soviet inventor Anatoly Yunitskiy also proposed an electromagnetic track encircling Earth, which he called "by wheel into space" (later, "String Transportation System"). When the velocity of the string exceeds 10 km/sec, centrifugal forces detach the string from Earth's surface and lift the ring into space. Andrew Meulenberg and his students, from 2008 to 2011, presented and published a number of papers based on types and applications of low-Earth-orbital rings as humanity's "stepping-stones-to-space". An overview mentions four applications of orbital rings. Birch's model Paul Birch published a series of three articles in the Journal of the British Interplanetary Society in 1982 that laid out the mathematical basis of ring systems. 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. 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 elevator cables made from materials with high-tensile-strength-to-mass-ratio. 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 Earth instead of staying fixed in space while 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 Earth. The cables which dangle from the ring are now geostationary without having to reach geostationary altitude or be placed into the equatorial plane. This means that using the Orbital Ring concept, one or many pairs of Stations