Editing Megastructure (section)

==Theoretical==
A number of theoretical structures have been proposed which may be considered megastructures.

===Stellar scale===
[[File:Dyson Sphere Diagram-en.svg|thumb|A cut-away diagram of an idealized [[Dyson shell]]—a variant on Dyson's original concept—1 [[Astronomical unit|AU]] in radius.]]
Most stellar scale megastructure proposals are designs to make use of the energy from a sun-like star while possibly still providing gravity or other attributes that would make it attractive for an advanced civilization.
* The [[Alderson disk]] is a theoretical structure in the shape of a disk, whose outer radius is equivalent to the orbit of Mars or Jupiter and whose thickness is several thousand kilometers. A civilization could live on either side, held by the gravity of the disk and still receive sunlight from a star bobbing up and down in the middle of the disk.
* A [[Dyson sphere]] (also known as a Dyson shell) refers to a structure or mass of orbiting objects that completely surrounds a star to make full use of its solar energy.
* A [[Matrioshka brain]] is a collection of multiple [[concentric]] Dyson spheres which make use of star's energy for [[computing]].
* A [[Stellar engine]] either uses the temperature difference between a star and interstellar space to extract energy or serves as a [[Shkadov thruster]].
* A [[Stellar engine#Class A (Shkadov thruster)|Shkadov thruster]] accelerates an entire star through space by selectively reflecting or absorbing light on one side of it.
* [[Topopolis]] (also known as Cosmic Spaghetti) is a large tube that rotates to provide artificial gravity.
* A [[Ringworld]] (also known as a [[Larry Niven|Niven]] Ring or a [[Freeman Dyson|Dyson]] Ring) is an artificial ring encircling a star, rotating faster than orbital velocity to create artificial gravity on its inner surface. A non-rotating variant is a transparent ring of breathable gas, creating a continuous microgravity environment around the star, as in the eponymous [[The Smoke Ring (novel)|Smoke Ring]].

Related structures which might not be classified as individual stellar megastructures, but occur on a similar scale:

* A [[Dyson sphere#Dyson swarm|Dyson swarm]] is a Dyson sphere made up of separately orbiting elements (including large habitats) rather than a single continuous shell.
* A [[Dyson sphere#Dyson bubble|Dyson bubble]] is a Dyson sphere in which the individual elements are [[statite]]s, non-orbital objects held aloft by the [[Solar sail|pressure of sunlight]].

===Planetary scale===
* A [[Bishop Ring (habitat)|Bishop Ring]], [[Halo (megastructure)|Halo]] or [[Orbital (The Culture)|Orbital]] is a space habitat similar to but much smaller than a Niven Ring. Instead of being centered on a star, it is in orbit around the star and its diameter is typically on the [[order of magnitude]] of a planet. By tilting the ring relative to its orbit, the inner surface would experience a nearly conventional day and night cycle. Due to its enormous scale, the habitat would not need to be fully enclosed like the [[Stanford torus]], instead its atmosphere would be retained solely by centripetal gravity and side walls, allowing an open sky.
* [[Globus Cassus]] is a hypothetical proposed project for the transformation of Planet Earth into a much bigger, hollow, artificial world with the ecosphere on its inner surface. This model serves as a tool to understand the World's real functioning processes.
* [[Shellworld]]s or paraterraforming are inflated shells holding high pressure air around an otherwise airless world to create a breathable atmosphere.<ref>[http://www.jbis.org.uk/paper.php?p=2009.62.32 "Shell Worlds – An Approach To Terraforming Moons, Small Planets and Plutoids"], K. L. Roy; R. G. Kennedy III; D. E. Fields, 2009, JBIS, 62, 32-38</ref> The pressure of the contained air supports the weight of the shell.
* Completely hollow shell worlds can also be created on a planetary or larger scale by contained gas alone, also called gravitational balloons, as long as the outward pressure from the contained gas balances the gravitational contraction of the entire structure, resulting in no net force on the shell. The scale is limited only by the mass of gas enclosed, the shell can be made of any mundane material. The shell can have an additional atmosphere on the outside.<ref>[http://yarchive.net/space/exotic/bubbleworld.html Dani Eder]</ref><ref>{{cite web | url=http://gravitationalballoon.blogspot.com.au/2013/12/ederworld-analyzed-concentric-gravity.html | title=Ederworld Analyzed (Concentric Gravity Balloons to Maximize Volume) | date=11 December 2013 | publisher=Gravitational Space Balloons | via=blogspot.com.au | access-date=30 June 2020 }}</ref>
*It can also refer to [[Terraforming|terraform]]ed or artificial planets with multiple concentric layers.

===Orbital structures===<!-- This section is linked from [[Space science]] -->
* An [[orbital ring]] is a dynamically elevated ring placed around the Earth that rotates at an angular rate that is faster than orbital velocity at that altitude, stationary platforms can be supported by the excess centripetal acceleration of the super-orbiting ring (similar in principle to a [[Launch loop]]), and ground-tethers can be supported from stationary platforms.
* The [[Bernal sphere]] is a proposal for a spherical space colony with a maximum diameter of 16 kilometers. It would have gravity at the equator, and gradually turn to zero G at the poles.
* [[Rotating wheel space station]]s, such as the [[Stanford torus]], are wheel-like space station which produce artificial gravity by rotation. Typical designs include transport spokes to a central hub used for docking and/or micro-gravity research.
* The related concepts, [[O'Neill cylinder|O'Neill]] and [[McKendree cylinder|McKendree]] cylinders, are both pairs of counter-rotating cylinders containing habitable areas inside and creating 1g on their inner surfaces via centripetal acceleration. The scale of each concept came from estimating the largest 1g cylinder that could be built from [[steel]] (O'Neill) or [[carbon fiber]] (McKendree).<ref>{{cite book |last=O'Neill |first=Gerard K. |title=[[The High Frontier: Human Colonies in Space]] |publisher=[[William Morrow and Company]] |date=1977 |isbn=0-688-03133-1 }}</ref><ref>{{Cite conference |url=http://www.zyvex.com/nanotech/nano4/mckendreePaper.html |title=Implications of Molecular Nanotechnology Technical Performance Parameters on Previously Defined Space System Architectures |conference=The Fourth Foresight Conference on Molecular Nanotechnology |conference-url=http://www.zyvex.com/nanotech/nano4.html |date=9–11 November 1995 |location=Palo Alto, California |last=McKendree |first=Thomas Lawrence }}</ref>
* Hollowed asteroids (or [[Space habitat#Other designs|Bubble worlds]] or [[Terrarium (space habitat)|Terraria]]) are spun on their axis for simulated gravity and filled with air, allowing them to be inhabited on the inside. In some concepts, the asteroid is heated to molten rock and inflated into its final form.<ref>{{cite book |last1=Cole |first1=Dandridge M. |author-link1=Dandridge MacFarlan Cole |last2=Cox |first2=Donald W. |title=Islands in Space: The Challenge of the Planetoids. |publisher=[[Chilton Book Co]] |location=Philadelphia |date=1964 |asin=B0007DZSR0 }}</ref><ref>{{cite book |last=Niven |first=Larry |author-link=Larry Niven |title=A Hole in Space |chapter=[[Bigger Than Worlds]] |pages=111–126 |publisher=[[Ballantine Books]] |location=New York |date=1974 |asin=B002B1MS6U }}</ref>
* A stellaser is a star-powered [[laser]] or [[maser]].

===Trans-orbital structures===
[[File:SpaceElevatorClimbing.jpg|thumb|right|One concept for the [[space elevator]] has it tethered to a mobile seagoing platform.]]
{{Main|Non-rocket spacelaunch}}
* A [[Skyhook (structure)|skyhook]] is a very long tether that hangs down from orbit.
* A [[space elevator]] is a tether that is fixed to the ground, extending beyond geostationary orbital altitude, such that centripetal force exceeds gravitational force, leaving the structure under slight outward tension.
* A [[space fountain]] is a dynamically supported structure held up by the momentum of masses which are shot up to the top at high speeds from the ground.
* A [[launch loop]] (or Lofstrom loop) is a dynamically supported 2000&nbsp;km long iron loop that projects up in an arc to 80&nbsp;km that is ridden by [[Maglev (transport)|maglev]] cars while achieving orbital velocity.
* [[StarTram|StarTram Generation 2]] is a [[Maglev (transport)|maglev]] launch track extending from the ground to above 96% of the atmosphere's mass, supported by magnetic levitation.
* A [[Tether propulsion#Rotovators|rotovator]] is a rotating tether where the lower tip is moving in the opposite direction to the tether's orbital velocity, reducing the difference in velocity relative to the ground, and hence reducing the velocity of rendezvous; the upper tip is likewise moving at greater than orbital velocity, allowing propellantless transfer between orbits. Around an airless world, such as the Moon, the lower tip can actually touch the ground with zero horizontal velocity.<ref>[http://www.tethers.com/papers/LEO2Lunar%2792.pdf "Tether Transport From LEO To The Lunar Surface"] {{Webarchive|url=https://web.archive.org/web/20110517191711/http://www.tethers.com/papers/LEO2Lunar'92.pdf |date=2011-05-17 }}, [[Robert L. Forward]], 1991, 27th Joint Propulsion Conference, AIAA 91-2322</ref> As with any [[momentum exchange tether]], orbital energy is gained or lost in the transfer.