Floating city (science fiction)

In science fiction, floating cities are settlements that strictly use buoyancy to remain in the atmosphere of a planet. However the term generally refers to any city that is flying, hovering, or otherwise suspended in the atmosphere.

In Jonathan Swift's satirical novel Gulliver's Travels, Swift envisioned Laputa, an island city that floated in the sky. The island was suggested to levitate above the Earth by use of the force of magnetism. In the 1920s, Hugo Gernsback speculated about floating cities of the future, suggesting that 10,000 years hence "the city the size of New York will float several miles above the surface of the earth, where the air is cleaner and purer and free from disease carrying bacteria." To stay in the air, "four gigantic generators will shoot earthward electric rays which by reaction with the earth produce the force to keep the city aloft."

Although Swift's proposal was intended as satire, Buckminster Fuller proposed the concept more seriously in the form of the Cloud Nine megastructure, in which he envisioned structural spheres that float freely in the sky, allowing passengers a migratory lifestyle and a solution to the depletion of Earth's resources. He proposed a 1-mile-diameter (1.6 km) geodesic sphere that would be heated by sunlight, functioning as a thermal airship.

A design similar to Fuller's Cloud Nine might permit habitation in the upper atmosphere of Venus, where at ground level the temperature is too high and the atmospheric pressure too great. As proposed by Geoffrey A. Landis, the easiest planet (other than Earth) to place floating cities at this point would appear to be Venus. Because the thick carbon dioxide atmosphere is 50% denser than air, breathable air (21:79 Oxygen-Nitrogen mixture) is a lifting gas in the dense Venusian atmosphere, with over 60% of the lifting power that helium has on Earth. In effect, a balloon full of human-breathable air would sustain itself and extra weight (such as a colony) in midair. This means that any large structure filled with air would float on the carbon dioxide, with the air's natural buoyancy counteracting the weight of the structure itself.

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