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Ringworld
Ringworld engineering
The "Ringworld" is an artificial ring about one million miles wide and approximately the diameter of Earth's orbit (which makes it about 600 million miles in circumference), encircling a Sol-type star. It rotates, providing an artificial gravity that is 99.2% as strong as Earth's gravity through the action of centrifugal force. Ringworld has a habitable flat inner surface equivalent in area to approximately three million Earth-sized planets. The majority of the surface is land interspersed with shallow, freshwater seas. On opposite sides of the ring are two large deep saltwater oceans, placed in counterbalance to one another. One of the large oceans, known as the "Great Ocean", contains one-to-one maps of all of the inhabited worlds of known space. The "Other Ocean" has many maps of a single world: the Pak Homeworld. Walls 1,000 miles tall along the edges retain the atmosphere. The Ringworld could be regarded as a thin, rotating slice of a Dyson sphere, with which it shares a number of characteristics. Niven himself thinks of the Ringworld as "an intermediate step between Dyson spheres and planets."[5]
-Ringworld has a habitable flat inner surface equivalent in area to approximately
three million Earth-sized planets.
-The Ringworld could be regarded as a
thin, rotating slice of a Dyson sphere, with which it shares a number of characteristics. Niven himself thinks of the Ringworld as "
an intermediate step between Dyson spheres and planets."
(I think of Ships and Orbital habitats as more common intermediate steps between planets and Ringworlds; like in 'The Culture' novels.)
Planets - Ships - Orbitals - Ringworlds - Sphereworlds/Dyson Spheres
http://en.wikipedia.org/wiki/Ringworld

Wish list:population centers beyond planetary(
http://en.wikipedia.org/wiki/The_Culture):Ships,Ring Orbitals,Sphere Orbitals,Ringworlds,Sphereworlds;ability to create & destroy planets,population centers,stars;AI competently using all advances & features.