Various designs of orbital systems have been attempted throughout the years. The most recent concept to be developed is a ring of particles of spacecraft around the earth designed to shade the earth from the sun. The driving force for this system is to inhibit global warming. While a novel concept, the sheer cost of the system is infeasible. Additionally, such a system would effectively illuminate the earth like the moon at night. It is important to note that this idea represents progress in space technology and the ability to combat global warming with technology.
http://www.livescience.com/technology/050627_warming_solution.html
More in line with the orbital ring concept I was focusing on is Paul Birch's "orbital ring." His idea proposes putting large objects in a low earth orbit. On this ring are "ring stations" that use electromagnetism to traverse along the ring. He determined that using such a system, the rotation of the ring could be controlled. This would allow the ring to rotate at some arbitrary speed. Most likely, the rotational velocity will match that of an earth day, effectively making the ring "geostationary." Birch also proposed having various rings at different inclinations to form a pseudo sphere of rings with space elevators connecting them to earth.
http://en.wikipedia.org/wiki/Space_fountain#Orbital_Ring
For a viable space habitat, there are many benefits to be reaped, and obstacles to overcome. Some of the benfits are financial, as it is believed that living and working in space will increase a worker's income and decrease the cost of living. Other benefits include adjustable gravity, as it is often related to the rotational speed of the station, constant and free access to solar energy, availability of resources from celestial bodies, large living areas for new populations, and, finally, easier trade with earth due to lack of gravity. Obstacles to overcome include lack of gravity, lack of life support systems, and the challenge of transportation and required energy costs.
http://en.wikipedia.org/wiki/Space_habitat
The author of "Ringworld," Larry Niven, devised an orbital habitat that orbits a sun. The ring worlds in his books have radii far greater than that of the earth. As for their construction, they have planar surfaces that face the sun and walls that retain the ring world's atmosphere. Due to their enormous size, these worlds have living surface areas far greater than that of the earth's surface. For instance, a typical ring world would have three million times the earth's surface area. The rotational speed of the ring world provides is with gravity that is 99.2% that of the earths.
http://en.wikipedia.org/wiki/Ringworld
The "Dyson sphere" is actually a construct formed by an array of "Dyson swarms." The simplest form of the Dyson swarm is the Dyson ring. The ring is actually constructed from solar power satellites and space habitats that orbit a star, much like a "ring world." A major benefit of this design is the ability to establish geostationary orbital stations piece by piece. This allows for assembly to take place over a long time. Dyson's aim was to devise a ring of solar collectors to harness the energy of the star, so the addition of rings to form a sphere and maximize solar collection. This idea could be adapted to form a Dyson ring of orbital habitats, or an orbital ring.
http://en.wikipedia.org/wiki/Dyson_Sphere
