Astroengineering is the application of scientific, economic, social, and practical knowledge in order to design, build, and maintain structures, machines, devices, systems, materials and processes in outer space. It is a form of megascale engineering. Typically, proposed feats of astroengineering are on the scale to remake an entire stellar system. Examples of astroengineering is the International Space Station and Tiangong-1 which represents humanity's ability to live in space for long or extended periods of time or even a lifetime. Besides the ISS and Tiangong-1, many nations and corporations have proposed plans for more space stations.
Typical megastructures that would be produced by astroengineering are hypothesized to be Dyson spheres, ringworlds, Alderson disks, Banks' Orbitals, Matrioshka brains, stellar engines such as Shkadov thrusters, and other artifacts produced by Type II and Type III civilizations on the Kardashev scale.
Some applications are becoming more relevant to our time period as advances in technology progress. The most basic astroengineering projects, like orbital towers (or orbital elevators) are becoming more likely due to such technological advances.
Resources is the one of the limiting factors preventing advances in astroengineering. Since astroengineering revolves around creating megastructures that could be millions of kilometers long, obtaining materials would require more than Earth's resources.
Even if resources become more abundant from other planets and planetary systems, energy limits what engineers would be able to accomplish. Creating large-scale structures requires large amounts of energy. Potential energy sources which would be used by a Type II or Type III civilization on the Kardashev scale include:
- A Dyson sphere or Dyson swarm and similar constructs are hypothetical megastructures originally described by Freeman Dyson as a system of orbiting solar power satellites meant to enclose a star completely and capture most or all of its energy output.
- Perhaps a more exotic means to generate usable energy would be to feed a stellar mass into a black hole, and collect photons emitted by the accretion disc. Less exotic would be simply to capture photons already escaping from the accretion disc, reducing a black hole's angular momentum; known as the Penrose process.
- Star lifting is a process where an advanced civilization could remove a substantial portion of a star's matter in a controlled manner for other uses.
- Antimatter is likely to be produced as an industrial byproduct of a number of megascale engineering processes (such as the aforementioned star lifting) and therefore could be recycled.
- In multiple-star systems of a sufficiently large number of stars, absorbing a small but significant fraction of the output of each individual star.
- White holes, if they exist, theoretically could provide large amounts of energy from collecting the matter propelling outwards.
- Capturing the energy of gamma-ray bursts is another theoretically possible power source for a highly advanced civilization.
- Type III civilizations might use the same techniques employed by a Type II civilization, but applied to all possible stars of one or more galaxies individually.
- They may also be able to tap into the energy released from the supermassive black holes which are believed to exist at the center of most galaxies.
- The emissions from quasars can be readily compared to those of small active galaxies and could provide a massive power source if collectable.
Another possibility is known as the Tiplerian Scenario, which would include sending Von Neumann probes with human-level artificial intelligence to distant planets and recreating themselves could lead to the possibility of achieving these engineering feats.
Astroengineering has been described in many works of fiction including:
- In the Ringworld series by Larry Niven, a ring a million miles wide is built and spun (for gravity) around a star roughly one astronomical unit away. The ring can be viewed as a functional version of a Dyson sphere with the interior surface area of 3 million Earth-sized planets. Because it is only a partial Dyson sphere, it can be viewed as an intermediary between Type I and Type II. Both Dyson spheres and the Ringworld suffer from gravitational instability, however—a major focus of the Ringworld series is coping with this instability in the face of partial collapse of the Ringworld civilization.
- Stephen Baxter's "Morlock" of The Time Ships occupy a spherical shell around the sun the diameter of earth's orbit, spinning for gravity along one band. The shell's inner surface along this band is inhabited by cultures in many lower stages of development, while the K II Morlock civilization uses the entire structure for power and computation.
- In the Star Trek: The Next Generation episode "Relics", the Enterprise discovers an abandoned Dyson sphere.
- In the Halo universe, The Forerunners created many planet-sized artificial megastructures, such as the Halo ringworlds, the 2 Arks and the Shield Worlds, which were micro - Dyson Spheres. One of the Precursor's most well known creations were the Star Roads. Immense, indestructible cables that connected planets and star systems.
A cut-away diagram of an idealized Dyson shell, a variant on Dyson's original concept, with a radius of 1 AU.
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- Colin R., McInnes (March–April 2005). "Dynamics of a particle moving along an orbital tower". Journal of Guidance, Control and Dynamics 28 (2): 380–382. ISSN 0731-5090. "The concept of an orbital tower has been discussed in the literature by many authors over a number of years. Although the concept is clearly futuristic, interest has recently been revived as a result of advances in materials science."
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- Kardashev, Nikolai. "On the Inevitability and the Possible Structures of Supercivilizations", The search for extraterrestrial life: Recent developments; Proceedings of the Symposium, Boston, MA, June 18–21, 1984 (A86-38126 17-88). Dordrecht, D. Reidel Publishing Co., 1985, p. 497–504.
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