I’ve come upon them in many books and science-fiction TV shows.
In science fiction and speculative (or exploratory) engineering, a megastructure is an enormous self-supporting artificial construct. The definition is often informal and varies from source to source, but generally requires at least one dimension to be in the hundreds of kilometers. Other criteria such as rigidity or contiguousness are sometimes also applied, so large clusters of associated smaller structures may or may not qualify. The products of megascale engineering or astroengineering are megastructures.
Megastructures appear as the product of technologically advanced spacefaring cultures.
The video game Halo also features them.
Megastructures are also a key part in the Alastair Reynolds novel Pushing Ice.
In Iain M. Banks‘ fictional Culture universe, an orbital (sometimes also simply called an O or a small ring) is a purpose-built space habitat forming a massive ring (though much smaller than a ringworld) rotating to simulate gravity.
Its inhabitants, often numbering many billions, live on the inside of the ring, where continent-sized ‘plates’ have been shaped to provide all sorts of natural environments and climates, often with the aim of producing especially spectacular results.
Unlike the Halos or orbitals, ringworlds are another matter.
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. Walls 1000 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.” To this end, one must understand that in the context of the books the Ringworld was described to have an approximate mass equal to the sum of all the planets in our solar system, and that the adventurers surmised that when the ringworld was built that it was made literally using all the planets in that system as their source of material down to the last asteroid and/or moon as the Ringworld star has no other bodies in orbit. In Ringworld’s Children it is additionally explained that it took the reaction mass of roughly 20 Jupiter masses to spin up the ring; thus the combined mass of the planets of the original system was that much larger than our solar system’s.
It has the flat inner surface of three million Earths!
To spin up the ring, it took the reaction mass of roughly 20 Jupiter masses!
And according to the author and creator of the concept, ringworlds are an intermediate step to a Dyson sphere.
A Dyson sphere (or shell as it appeared in the original paper) is a hypothetical megastructure that was originally described by Freeman Dyson as a system of orbiting solar power satellites meant to completely encompass a star and capture its entire energy output. Dyson speculated that such structures would be the logical consequence of the long-term survival of technological civilizations, and proposed that searching for evidence of the existence of such structures might lead to the detection of advanced intelligent extraterrestrial life.
I find the whole concept mindboggling.
Still, they are an important part of science-fiction. I’ve actually used them as well in my story Post-Mortem, taking place thousands of years later in the Galactic Rim universe.
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