I often drop the term megastructures but I’m not sure whether or not most of my readers are familiar with these theoretical science fiction constructs. So I figured I might as well post an overview of the most interesting constructs here. In general when I say megastructures I am talking about huge scale, man made planet or solar system sized space habitats.
The ultimate megastructure is probably a Dyson Sphere. Imagine the following: you gather up all the available matter in the solar system and use it to construct a gigantic sphere that completely encases the sun. You then terraform the inside of the shell into habitable environment, and you build space ports, observatories and industrial buildings. This setup would give you a huge living area for your population and allow your civilization to intercept all of the solar energy produced by the sun.
If you have ever played Freelancer, you actually get a chance to fly inside one of these things. Of course there are many problems with this setup. For one, a shell like this would not have gravitational interaction with the parent star, nor with anything build on it’s surface. It would need strong propulsion systems on the outside to prevent it from drifting off course and crashing into the sun. Furthermore it would need artificially generated fields to provide gravity on the inside of the shell. It would also be extremely vulnerable to meteorite and comet strikes from the outside.
Therefore a Dyson Shell concept is mostly science fiction. It’s variants known as Dyson Swarms and Dyson Bubbles are more realistic and they may have a chance of being constructed one day. They eschew the idea of uniform shell and instead propose to build a fleet of solar powered satellites and habitats which would orbit the star in a dense formation. The aim would still be to intercept almost all of the solar energy, but individual orbital constructs could be gravitationally locked to the star, making the system much more stable – though much less impressive.
Matrioshka Brain is a Dyson Sphere system construct which is used not as a habitat, but rather as a computational device. In other words it is a solar system sized computer – usually a brain of powerful post-singularity artificial intelligence. This of course does not mean that humans cannot inhabit such a structure. It is possible that making certain parts of the brain habitable to humans, or using humans to service and repair the construct would be possible. Simply the primary function of this mega structure is to provide computational facilities.
Because of this function Matrioshka Brain would be much more dense than a regular sphere. It would usually contain several nested shells or swarms to maximize the use of the solar output and minimize signal propagation delay.
The name derives from the Russian nesting Matrioshka dolls.
A classic Dyson Shell would probably be the ultimate human habitat providing vast inner surface for human settlement and cultivation. It’s swarm and bubble variants are much more limited with respect to habitable surface relying on smaller, independent space habitats. Alderson Disk is an alternative to a Dyson Sphere which aims to provide a similar amount of habitable surface, using a much more stable system.
Instead of building a gigantic sphere, we instead construct a flat disk several thousand miles thick with the star at it’s center. Humans could then inhabit both of its sides. Unlike the Dyson Shell, a flat platter would be gravitationally locked with the star. Furthermore it’s thickens and size would give the disk it’s own gravitational pull that would be directly perpendicular to it’s surface allowing it to have it’s own atmosphere.
The main problem with this structure would be the fact that the area of the disk near the sun would be just as uninhabitable as it’s outer circumference due to extreme heat and lack of it respectively. At least not without shielding. Furthermore, an Alderson Disk would lack day/night cycle – unless it could be made to bob up and down with respect to the sun.
We established that both the Dyson Shell and Alderson Disk while awesome have certain flaws. The shell is intrinsically unstable while the disk has rather small ratio of habitable space as compared to it’s total surface area. Ringworlds, originally imagined by Larry Niven provide yet another alternative. Instead of a sphere of a disk, build a massive ring (with a radius of approximately 1 au) that encircles the sun. Then create habitable environment on the inner surface.
Naturally such a construct would not have a day/night cycle either, so you need a smaller ring of “shadow” plates orbiting closer to the sun that would simulate it. Unfortunately the ring is not very stable either, and would tend to drift out of alignment with the star just as the Dyson Shell.
The most popular ring worlds are probably those featured in the halo games.
Orbitals are small scale ringworlds that do not encircle a star. Instead they rotate around their own axis to provide simulation of gravity and orbit around a star as normal. Their orbital position, and alignment with respect to their star allows them to have regular seasons and a day/night cycle just like a planet would. They are also much more stable than a full scale ring world.
The concept was originally coined by Ian M. Banks in his Culture novels. Also, it is a little known fact that the structures featured in the Halo games are not Ringworlds but rather orbitals (they do not encircle a star). Most people tend to erroneously call them ring worlds because they are more familiar with the work of Larry Niven.
Let’s move to a smaller scale constructs. O’Neill Cylinder is a space habitat consisting of two large, counter-rotating cylinders, 5 miles in diameter and 20 miles long. The centrifugal force generated by their rotation provides artificial gravity on the inner surface which can be made habitable. Parts of the surface would be made transparent to allow sunlight inside of the tube.
The cylinder could be a stand alone space habitat, or a member of a Dyson Swarm.
Another variation on the ring world theme is Topopolis. Instead of open ring structure, we have an extended O’Neil Cylinder that encircles a star many times in a torus knot like formation.
Topopolis, often compared to space spaghetti was used by both Lary Niven and Ian M. Banks in their novels.
Also known as the poor man’s O’Neil Cylinder, Bernal Sphere is a hollow spherical space habitat one mile in diameter. It would rotate around it’s own axis providing artificial gravity on it’s inner surface. It would be filled with breathable air and have transparent panels that would allow sunlight inside.
A Bernal Sphere could theoretically support population of 20,000 to 30,000 people. Yet another candidate habitat which could be a member of a Dyson Swarm.
Yet another smaller scale theoretical habitat. It would be a torus or donut shaped rotating ring with habitable environment on it’s inner shell. The ring would be connected via massive spokes to a central hub which would house a space port. The hub facing part of the ring would likely be made transparent and a system of mirrors on or below the hub would channel sunlight down to the inner surface of the ring.
Stanford Torus would be capable of supporting 10,000 to 140,000 residents, and the central hub would make it very easy to dock with, or run industry that requires low or no gravity without actually ever leaving the station. If you ever read the Gaea Trilogy by John Varley this is precisely the type of construct he described.
Finally, I bring you the Globus Cassus, also known as the open source mega structure. It is a project started by Swiss architect Christian Waldvogel presenting a conceptual transformation of Planet Earth into a much bigger, hollow, artificial world with a habitable ecosphere on its inner surface.
The structure would use all of Earth’s matter as building material. Sunlight would enter through two large transparent window panes windows, and gravity would be simulated by the centrifugal effect. Humans would live on two vast land masses that would face each other, connected through the empty center. Only the equatorial zones would be habitable. Tropical zones would have thin atmosphere and gravity while polar zones would have neither but could be used for storage and/or low zero industry.
Did I forget about any megastructures here? Which megastructure is your favorite? Which one would you love to visit? I have been always fascinated by Dyson Shells. Even though they are the least feasible to construct, I would totally love to take a tour of one of them. On the other hand the Globus Cassus project just gives me the creeps. I don’t know why but the mere idea of dismantling our home world and making it into a hollow space habitat seems wrong on way to many levels. I guess I wouldn’t mind seeing another uninhabited world transformed this way, but I can’t imagine watching this happen to Earth.
How about you?