NASA’s Hollowed Sphere Colonies
NASA's Cylindrical Colonies or Hollowed Sphere Colonies began as a concept in the 1970's. This concept was revisted and re-engineered again in the 2000's with Kaplana One. These designs were part of a larger vision for "space" colonization, where humanity would create self-sustaining habitats in space. The idea was to construct massive cylindrical or spherical structures, rotating to create artificial gravity using centrifugal force, with their inner surfaces terraformed to mimic Earth-like conditions.