Huge floating structures that harness the energy of the stars can be home to humanity. True, building them will be an incredible task. Giant ring worlds orbiting distant stars have become iconic in science fiction. Their pure landscapes, enclosed in thin ring structures, thrill our imaginations. The ring world has become a common motive, a future base for humanity.
“This is all nonsense, of course,” says retired professor Freeman Dyson. It was Dyson who popularized the idea of these megastructures; they eventually became known as Dyson spheres. Dyson, in turn, "borrowed the idea" from science fiction writer Olaf Stapledon in his 1937 Star Maker novel, in which a traveling earthling encounters similar megastructures that absorb the energy of nearby stars. Although Dyson saw these spheres as shells of orbital structures in order to absorb the maximum amount of energy from the star, science fiction writers admit the possibility of habitable spheres covering the star.
Ten years after Dyson's 1960 paper on such structures was published in Science, Larry Niven decided to use the equatorial ring as the Dyson sphere as the basis for his novel Ringworld.
The Ring Worlds have since featured in the Halo video game series, the 2013 film Elysium and Ian Banks' novel Culture. In Halo, they are giant artificial worlds where humans can live on the inside of the ring while the outside is protected by a strong shell. In Elysium by Neil Blomkamp, meanwhile, the ring world revolves around the Earth and looks more like a space station. How do you build such rings in the real world?
As with any field, size matters. The ring world is a megastructure, and its construction will require an enormous amount of materials and energy.
Collecting asteroids
Science fiction writer and former astronomer Alastair Reynolds believes that “There is enough material in the Kuiper belt to build anything. We could absorb all the small asteroids, filter out volatile materials, leave pure rock and build incredible structures out of it."
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However, there are places where this material is in abundance. Kuiper Belt - it is a region of the solar system that extends approximately 2.97 billion kilometers beyond the orbit of Neptune. It is filled with asteroid-like bodies that could be an ideal source for raw materials.
Astronomer Katie Mack disagrees with him. She says: "The Kuiper belt is pretty diffuse and you have to assemble and disassemble quite a few bodies to collect the right amount of material."
If - and this is a big if - the society of the future has enough time and capacity to collect and transport material from the Kuiper belt to the required orbit, there will be enough raw materials to build the ring world. However, the question remains whether investing this amount of time and resources will be worthwhile.
The ring world must also support some form of gravity; otherwise, everything, including the atmosphere necessary for life, would float away into deep space. The most common way to generate artificial gravity is to generate centrifugal force through rotation. However, getting such a massive object to rotate at the required speed will be a colossal task.
The rotational forces must be evenly distributed, otherwise the structure may tear itself apart. Fortunately, there is no friction in space, and rotation at the desired speed will not slow down.
The larger the diameter of the ring world, the more forces will act on the rotating structure. According to Mack, the strength of these shear forces acting on the ring will depend on "how close you are to the star and how much gravity you need."
Unknown power
If we assume that the ring world will have the same diameter as the Earth's orbit (about 300 million kilometers) and require gravity of 1G, it would have to rotate at a speed of about 1.9 million kilometers per hour. The forces acting on it will be so powerful that, according to Mack, "we'll have to find a new way to tie the atoms together."
One of the theoretical solutions to this technical problem may be hidden in some form of piezoelectricity. Simply put, the material can be artificially reinforced by passing electricity through it.
However, given the size of the ring and the energy it needs, the effectiveness of this colossal enterprise is once again beginning to be questioned. Power will have to be evenly distributed throughout the structure, while reducing the risk of a catastrophic power failure to zero.
The ultimate challenge will be to keep the ring world in a stable orbit around the star. Reynolds recalls that shortly after Larry Niven's Ringworld was published, "fans calculated that if the Ringworld moved a little closer to the star, the balance would be upset, the structure would drift and eventually explode."
Niven took care of this in the later novels of The Ring World, attaching rockets to the outer edges of the structure, which would permanently stabilize its position and ensure its centering relative to the star.
If we assume that the society of the future will have large-scale technical capabilities for the construction of the ring world, the issue of strengthening the structure and maintaining its orbital stability will be resolved, what will they do with it next?
In Culture, orbital stations were used as large dwellings, while in the Halo series they were doomsday devices designed to detonate and destroy dangerous infection. Dyson saw his realms as a means to maximize the energy harvest from a star, not as an alternative to terraforming to make them fit for humans.
Mack says: "We could create a ring world so as not to terraform existing worlds." However, she believes that this solution may not be the most effective. The scientist believes that "any society that can easily build a structure like the ring world can easily find a rocky planet and terraform it at its discretion."
Although the technology for terraforming is different from what is required to build an orbital ring, the level of overall technical progress will be about the same. On the other hand, for all their theoretical splendor, ring worlds remain scientifically inaccessible and ineffective examples of stellar engineering.
Ilya Khel