The Star Trek: The Next Generation episode “Relics” featured the theoretical structure known as a Dyson Sphere, a huge shell that encompassed an entire star to capture its energy to be used by the inhabitants of the sphere. The design seen in the episode is actually known as a Dyson Shell, but used the more popular term of sphere.
Originally described by Freeman Dyson, such a “sphere” would be a system of orbiting solar-power satellites meant to completely encompass a star and capture most or all of its energy output. Dyson speculated that such structures would be the logical consequence of the long-term survival and escalating energy needs of a technological civilization, and proposed that searching for evidence of the existence of such structures might lead to the detection of advanced intelligent extraterrestrial life.
Since then, other variant designs involving building an artificial structure or series of structures to encompass a star have been proposed in exploratory engineering or described in science fiction under the name “Dyson sphere”. These later proposals have not been limited to solar-power stations. Many involve habitation or industrial elements. Most fictional depictions describe a solid shell of matter enclosing a star, which is considered the least plausible variant of the idea. In May 2013, at the Starship Century Symposium in San Diego, Freeman Dyson repeated his comments that he wished the concept had not been named after him.
For the interior of a Dyson sphere to be habitable to most humanoid lifeforms, the radius of the sphere must be such that habitable temperatures (5 – 30 °C) are maintained. The radius would therefore depend on the size and the energy output of the star around which the sphere would be constructed; if a Dyson sphere were to be constructed around the Earth’s sun, the radius would have to be approximately one astronomical unit. At such a radius, the interior surface area would be about 28 ×1016 km2, or 550 million times the entire surface area of the planet Earth. Such a surface area could easily support the lives of many quadrillions of beings.
Unsurprisingly, due to the almost immeasurable amounts of effort, resources and time required to construct such an immense structure, only one Dyson sphere has ever been discovered. This particular sphere encased a G-type star and had a diameter of 200 million kilometers, giving it an internal surface area of approximately 250 million M-class planets. As no radiant sunlight or solar wind escaped from the sphere, starships were not able to detect it until they were almost on top of it. As a result, the USS Jenolan crashed onto it in 2294 after being pulled in by the sphere’s immense gravity well while en route to the Norpin colony. In 2369, the USS Enterprise-D discovered the Jenolan and investigated the sphere. The sphere was deserted because the star around which it was constructed was highly unstable.
The concept of the Dyson sphere was the result of a thought experiment by Dyson, when he theorized that all technological civilizations constantly increased their demand for energy. He reasoned that if our civilization expanded energy demands long enough, there would come a time when it demanded the total energy output of the Sun. He proposed a system of orbiting structures (which he referred to initially as a shell) designed to intercept and collect all energy produced by the Sun.
Dyson’s proposal did not detail how such a system would be constructed, but focused only on issues of energy collection. Dyson is credited with being the first to formalize the concept of the Dyson sphere in his 1960 paper “Search for Artificial Stellar Sources of Infra-Red Radiation”, published in the journal Science. However, Dyson was not the first to advance this idea. He was inspired by the mention of the concept in the 1937 science fiction novel Star Maker by Olaf Stapledon, and possibly by the works of J. D. Bernal and Raymond Z. Gallun, who seem to have explored similar concepts in their work.
So can it work?
Some ideas to build a fixed-in-place ‘Dyson sphere’ are currently beyond humanity’s engineering capacity. However, parts of the technology, like orbiting satellites and solar sails, have already been developed. Deployment of spacecraft and satellites using photovoltaics might be seen as the first small steps towards building a Dyson swarm. However, the number of craft required to obtain, transmit, and maintain a complete Dyson sphere far exceeds our present-day industrial capabilities.