DYSON SPHERES


A simplified cutaway diagram of a Type II Dyson Sphere

Type I Dyson Sphere
Tech Level: 20
Light Pressure Dyson Sphere
Tech Level: 20
Type II Dyson Sphere
Tech Level: 22
Mobile Dyson Sphere
Tech Level: 23
Solid Dyson Sphere
Tech Level: 25
Sunken Dyson Sphere
Tech Level: 27

Dyson Spheres are enormous physical shells constructed to englobe stars. Dyson Spheres have proven to be one of the most mind-boggling concepts in science fiction, representing an almost incomprehensible scale of engineering that would seem godlike to the people of today.

Highly specialized types of Dyson Sphere objects, like Matrioshka Brains, will be discusses in other articles.

The name comes from Freeman Dyson, a renowned astronomer who was part of Project Ozma in 1959, the very first effort to find alien civilizations through radio and optical astronomy. In that year he wrote a paper called "Search for Artificial Stellar Sources of Infrared Radiation" in the publication Science. He suggested that as a civilization advanced, its energy needs would grow exponentially, so they'd turn to the most potent nearby source of power--their sun--and englobe it to trap all of its energy output directly. He suggested looking for large, low-level infrared sources (a Dyson Sphere would block all sunlight but would still have to shed excess heat) that would be a telltale sign of such structures.

Dyson spheres have become one of the much-loved concepts in science fiction, and have appeared in a great many science fiction sources. The earliest known source of the concept is in Olaf Stapledoní The Star Maker from 1937, which helped to inspire Dysonís more serious scientific speculation twenty two years later. Other novels with Dyson Spheres include Across A Billion Years by Robert Silverberg, Farthest Star and Wall Around A Star by Jack Williamson and Frederick Pohl, The Ring of Charon and The Shattered Sphere by Roger Macbride Allen, the Orbitsville series by Bob Shaw, and The Time Ships by Stephen Baxter. The Star Trek: The Next Generation episode, "Relics," also featured a Dyson Sphere, and is probably the example best known to the public at large.

A Dyson Sphereís primary purpose would be energy gathering. As Dyson pointed out in his paper, humanityís energy needs have been growing exponentially all throughout its history, and if this trend continues there will come a time when Earth-based means of creating energy simply wonít be enough. There is, however, an extremely potent and long-lived power source just 93 million miles from us--the Sun. Englobing it to trap all its energy would supply humanity with the power to support a population of trillions and perform technological feats unimaginable today.

A secondary purpose of such a construct would be living space. Create a Dyson Sphere with a radius of Earthís distance from the sun (or whatever the radius of a starís life zone would happen to be), the inner surface of the sphere would receive just enough sunlight to support liquid water and organic life. The inner surface would be lined with soil, seeded with flora and fauna, and pressurized. If the entire inner surface of a life-supporting sphere is used, it would create a habitable surface area equal to nearly one billion Earth-sized worlds.

Dyson Spheres could also be used for other, secondary purposes, such as defense, quarantine, herding stars, and so on.

Advanced artificial gravity technology would be an absolute necessity if one wanted to use any part of the Sphere for an artificial habitat. A Dyson Sphere could be made to rotate, producing spin gravity along the inner surface close to its rotational equator. To use more than just the equatorial regions, however, true artificial gravity technology would have to be developed and employed on a massive scale.

Creating a Dyson Sphere would be an enormous undertaking for any civilization, and would require entire planets to be gutted and disassembled for raw materials. Construction time is estimated to be from several centuries to many millennia for all but the most god-like cultures. Because they would be such enormous investments for the building civilization, Dyson Spheres would be designed to be as long-enduring as possible.

Because the laws of entropy still apply and even the most advanced energy gathering can never be completely 100% efficient, Dyson Spheres will leak thermal radiation--waste heat. So even though all of the starís radiative output is intercepted by the sphere, these objects will still glow in the infrared spectrum. Astronomers are well aware of this telltale signature, and despite decades of searching, no Dyson objects have ever been found by human telescopes.


TYPE I DYSON SPHERE
Tech Level: 20

These are also sometimes called Dyson Swarms, and are what Freeman Dyson had actually proposed in his original 1959 paper. The more solid versions of a Dyson Sphere came later, mostly from science fiction. An example of a Type I Dyson Sphere, called the Array, is occasionally seen in the comic book series Tom Strong. Olaf Stapledonís seminal novel The Star Maker also had this kind of sphere.

A Type I Dyson sphere is made up of many billions, if not trillions, of small independently-moving bodies circling the sun. Their orbits are layered and synchronized in such a way that they intercept all of the light given off by the star.

A Dyson swarm may not start out as a planned object; it may evolve over time as the owning civilization expands and adds more and more habitats and solar power collectors as it advances. A Dyson Swarm may be a necessary preliminary step to creating the more advanced versions of these objects, as all the construction materials and assembly machinery would have to be carefully laid out in various orbits before actual assembly began.

The thickness of the swarm would vary depending on its exact architecture and working components. The objects may be held in a tight layer only a few thousand miles thick, in order to facilitate easier transportation between all elements. Or it may be many millions of miles thick, with inner elements gathering the majority of the sunlight and outer elements containing enclosed habitats or manufacturing facilities.

Type I spheres would also be the easiest of this class of object to spot by distant telescopes, as it would leak the most amount of thermal radiation.


LIGHT PRESSURE DYSON SPHERE
Tech Level: 20

Also called a Gossamer Sphere or a Dyson Bubble, this is basically a star-englobing solar power array. This type of star envelopment is accomplished with a thin framework and large swaths of micron-thin solar-sail like material, used to gather the sunlight for the star for power. This energy is then beamed to nearby locations for use or storage.

Light pressure from the star alone is enough to keep the sphere rigid and "inflated," though it may also be rotated to help ensure structural stability. The sphere and its components need not revolve around the star either; the entire bubble may be nothing more than a collection of super-sized statites, counter-acting the starís gravity through photon pressure alone.

Unlike other types of Dyson Sphere, a Gossamer Sphere need not take possible habitation into account, and can be constructed at a radius much closer in to the central star. The sphere may be a loose swarm or one consolidated sphere; both configurations would work as well for energy-gathering. A single consolidated Sphere would require less over all material, where as multiple layers of a swarm would allow for more redundancy.

In fact, a Gossamer Sphere would require much less building material than any other object of this class. Where other Dyson Spheres would require the disassemble of most or all of the terrestial bodies in a solar system, a Dyson Bubble could be built using only the mass of a single large moon.


TYPE II DYSON SPHERE
Tech Level: 22
The Enterprise D is pulled reluctantly into the interior of a Type II Dyson Sphere. From the Star Trek: The Next Generation episode "Relics." Image copyright Paramount.

This is a single, consolidated, unbroken sphere around a star, sometimes also called a Suprastellar Sphere or a Dyson Shell. When most sci-fi fans mention a Dyson Sphere, this is the version they are usually referring to. The earliest known version appeared in Robert Silverbergís novel Across a Billion Years.

Type II Dyson Spheres face a number of difficulties Type Iís do not. With a Dyson Swarm, each component is in its own independent orbit about the central star, so the entire system is inherently stable. The same with enormous statites whose orbital motion is held in check by light pressure, as with a Gossamer Sphere.

Not so with a solid shell. Because the same mass is held at the same distance at every point around the star, the shellís net gravitational influence on the star is negligible. This means is that the starís gravity doesnít "anchor" it at all--it can easily drift off center and crash into the star with the slightest bit of relative force. Therefore, attitude jets or some other form of station keeping system would be needed, and given the shellís size and mass, such a system would probably consume a significant percentage of the energy gathered from the star.

Another major engineering hurdle is structural stress. Dyson shells, even ones with gravitic technology in place, are assumed to be rotating at least slowly, if from nothing else the accumulated angular momentum of the central starís motion through space. It may also be rotated to keep its rigid spherical shape, or to produce gravity through centripetal force on the interior surface around the equator. Even tiny tidal forces acting on a structure millions of miles across tend to accumulate to staggering proportions, threatening to tear apart any material substance holding the shell together.

Calculations show that the material holding a shell together would have to be at able to handle stress many times that of the very best projections given to carbon nanotube structures today. In other words, it would have to be at last several dozen times stronger than materials that would hold a Space Elevator together, or at least several thousand times stronger than the best steel cable currently manufactured. No known material can currently handle such a colossal load. Builders of a Dyson Shell may have to augment physical materials with powerful magnetic fields, or be forced to create major breakthroughs in materials science before they could even begin to think about construction.

Another factor to consider is that the shell is assumed to be relatively thin--about 3 to 10 meters thick at most-- and would exert negligible gravity on anything on its inner surface. If left completely on its own, anything on the inner surface would eventually drift off the surface and go into slowly decaying solar orbit. Since one of the assumed primary purposes of a shell is to produce a vast livable habitat, this would of course be counter-productive.

Artificial gravity would have to be generated on the inner surface in some way. One method is to spin the shell up, similar to Larry Nivenís Ringworld, at over 7.7 miles a second to produce one Earth gravity along the equator. This gravity would gradually fade away the farther one got away from the equator, but would still provide the means to keep air and soil on the surface for millions of miles. Also like on the Ringworld, immense walls could be built to keep the atmosphere from leaking out along the habitable equatorial zones.

It was pointed out by Niven that if one wanted to spin a Dyson sphere, it would be best to make it a hollow disk instead, similar to an old film canister, for structural support reasons.

An alternative is to generate the gravity by some unknown artificial means, perhaps through an advanced form of quantum gravity manipulation that remains unknown to us in the early 21st century. Such gravitic generators would have to be built on an enormous scale in order to provide the proper gravity over the surface area of the entire Dyson Shell, and may consume a significant amount of power gathered from the central star, depending on how exactly they would work.

A Dyson Shell would require the disassembly of an entire solar system for building materials. Not only the basic structure of the shell, but also for all the air, water, soil, and organic material that will be needed to create the inner surface habitat. Any body not used in construction would likely be ejected from the system altogether, not only to avoid the possibility of any collisions, but also to prevent the accumulation of even small tidal forces on the shell.

Creating a day-night cycle for the inner surface would be another challenge. Perhaps the most straightforward method is to create a smaller sphere inside the larger one. This inner sphere would more closely resemble a spherical cage or a tremendously over sized eggbeater. It would rotate faster than the larger outer sphere and cast shadows on the inner surface in order to create a "night" in a similar way that the Shadow Squares did in Larry Nivenís Ringworld. This rotating "shadow cage" would probably also be the primary energy-gathering component of the system.

The Dyson Sphere in the Star Trek: The Next Generation episode Relics was mentioned to be able to polarize the sphere habitatís upper atmosphere in order to simulate night, but how that could be done, albeit on such a massive scale, is unknown.

Another method would be have the sphere separated into different sections, each with a separately supported roof structures. This way, different environments around the sphere could have customized day-night cycles, and could provide additional protection for ecosystems from solar radiation in the absence of the planetary magnetic fields that we enjoy on Earth. Making the roofs selectively light-reflective could also help to center the sphere on the central star at least partially through light pressure, and the roof could support a magnetic field that could do the same through the solar wind.

Roof support structures would dot the inner surface. Given the ultra-tensile strength of the basic sphere construction material, it wouldnít be too much of a stretch to envision towers fifty or a hundred miles high even in Earth-normal gravity, holding a roof a few micron thick held rigid by magnetic fields. Or, given the presumed presence of advanced artificial gravity technology, gravitic projectors or generators needed to hold such a roof in place may dot the surface instead.

Concerns have been raised about the vulnerability of such an immense consolidated habitat to outside disasters. The impact of a major body, either accidental or deliberate, anywhere on the sphere would threaten the entire billion-Earth-plus habitable surface, not only from a puncture but from destabilizing the sphere in regards to its central star. Even if attitude jets and other safeguards kicked in, the offset of the Sphere could create widespread loss of life and ecological degradation, as one part of the sphere lurches closer to the sun and another is pulled farther away.

A way around this is to have many individual habitats instead of one huge consolidated one, each one independent from the others with its own environmental support system. The framework of the sphere itself may be constructed with the ultra-tech equivalent of "crumple zones" found in todayís cars. In the event of a catastrophic impact, these crumples zones would absorb most of the incoming energy by deforming to self-destruction. All or part of the sphere may shatter as a result, but the framework would absorb the vast majority of the incoming force, sparing the people and ecologies inside the habitats. The habitats could then be herded into temporary orbits while repairs were made.

Like on most space-going habitats, near one-hundred-percent efficient recycling systems would be an absolute necessity to keep the sphere or any of its sub-habitats ecologically optimized. However, engineering such environmental system on such a colossal scale would be unprecedented. Nature has only created one known system of integrated ecosystems as large as a planet. Creating and sustaining one artificially a billion times that size would be an unprecedented feat of engineering rivaling that of building the sphere itself.


MOBILE DYSON SPHERE
Tech Level: 23

It is possible that with very advanced forms of electromagnetic and gravity manipulation, both Type I and Type II Dyson Sphere could be made mobile. One popular idea is to leave one or more large apertures open in the general Sphere structure, and to use extremely powerful and advanced magnetic fields to draw off a large jet of plasma from the star. This sustainable plasma jet would very, very gradually move the star, and the sphere would move along with it.

Alternately, the Sphere itself may generate immense magnetic or artificial gravitic fields that would slowly drag the star toward one side of it. The Sphere would be constantly repositioning itself to maintain a proper distance from its primary and slowly drag the star along, in effect acting like stellar tug boat.

In either scheme, the accelerations experienced by the star would be extremely gradual, and would take centuries if not thousands of years to build up any kind of appreciable speed.


SOLID DYSON SPHERE
Tech Level: 25

A solid Dyson Sphere has the same proportions of a Dyson Shell, but is solid all the way through to just above the starís surface. Even with matter conversion, it would take the material resources of dozens of star systems to construct such a mammoth artifact. It could hold perhaps a quadrillion inhabitants with millions of continent-sized habitats throughout its volume.

The purpose of a solid Dyson Sphere may go beyond just living space and energy gathering. In the novels The Ring of Charon and The Shattered Sphere by Roger MacBride Allen, advanced alien artificial intelligences used such spheres to apparently convert stars into a more advanced (but unspecified) power source. In the novels Farthest Star and Wall Around A Star by Frederick Pohl and Jack Williamson, a solid Dyson sphere was used as a lifeboat to transport survivors away from an exploding galaxy.


SUNKEN DYSON SPHERE
Tech Level: 27

A scheme that would require insanely powerful and advanced material technology, this idea proposes constructing an energy-gathering lattice surrounding the interior fusion-generating cores of stars. The sphere is "sunk" thousands of miles deep into the star itself, just above the core where the fusion that powers the star takes place. The sphere in this case would be an open framework, or "cage," in order to allow the starís hydrogen fuel to still freely flow into the core and fusion byproducts to flow out.

Unlike other types of this technology, a sunken Dyson Sphere would not trap all of the starís energy (completely blocking the flow of hydrogen and fusion byproducts in the interior would lead to a collapse of the core and a subsequent nova.) However, given the far greater density of energy gathered near the core, the total amount of power obtained would remain about the same.

How exactly such a sphere could be constructed, much less put in place and maintained, is unknown. Its possible that given the lofty Tech Level, it may not be composed of recognizable matter at all, but may be constructed of pure force fields, cosmic strings, wormhole openings, or a combination thereof.


FURTHER INFORMATION

http://www.nada.kth.se/~asa/dysonFAQ.html

http://www.orionsarm.com/civ/Dyson_Spheres.html

http://users.rcn.com/jasp.javanet/dyson/


Article added 10/20/07

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