Megascale engineering (or macro-engineering) is a form of exploratory engineering concerned with the construction of structures on an enormous scale. Typically these structures are at least 1,000 kilometers in length—in other words, at least 1 megameter, hence the name. Such large-scale structures are termed megastructures.
In addition to large-scale structures, megascale engineering is also defined as including the transformation of entire planets into a human-habitable environment, a process known as terraforming or planetary engineering. This might also include transformation of the surface conditions, changes in the planetary orbit, and structures in orbit intended to modify the energy balance.
Megascale engineering often plays a major part in the plot of science fiction movies and books. The micro-gravity environment of outer space provides several potential benefits for the engineering of these structures. These including minimizing the loads on the structure, the availability of large quantities of raw materials in the form of asteroids, and an ample supply of energy from the Sun. The capabilities to employ these advantages are not yet available, however, so they provide material for science fiction themes.
Quite a few megastructures have been designed on paper as exploratory engineering. However, the list of existing and planned megastructures is complicated by the fact that there are no universally agreed-upon criteria for a structure to be called a megastructure. By the most strict definitions, no megastructures currently exist (with the space elevator being the only such project under serious consideration). By more lenient definitions, the Great Wall of China (6.7 Mm) counts as a megastructure.
A more complete list of conceptual and existing megastructures, along with a discussion of megastructure criteria, is found under megastructure.
Of all the proposed megastructures, only the orbital elevator, the Lofstrom launch loop, and Martian or lunar space elevator concepts could be built using conventional engineering techniques, and are within the grasp of current material science. Carbon nanotubes may have the requisite tensile strength for the more technologically challenging Earth-based space elevator, but creation of nanotubes of the required length is a laboratory exercise, and adequate cable-scale technology has not yet been shown at all.
The assembly of structures more massive than a space elevator would likely involve a combination of new engineering techniques, new materials, and new technologies. Such massive construction projects might require the use of self-replicating machines to provide a suitably large "construction crew". The use of nanotechnology might provide both the self-replicating assemblers, and the specialized materials needed for such a project. Nanotechnology is, however, another area of speculative exploratory engineering at this time.
- Ćirković, Milan M. (2006). "Macro-Engineering in the Galactic Context: A New Agenda for Astrobiology". In Viorel Badescu, Richard Brook Cathcart, Roelof D. Schuiling. Macro-Engineering: A Challenge for the Future. Springer. p. 281. ISBN 1-4020-3739-2.
- Timofeev, M. Y.; Kardashev, N. S.; Promyslov, V. G. (June 2000). "A search of the IRAS database for evidence of Dyson Spheres". Acta Astronautica 46 (10–12): 655–659. Bibcode:2000AcAau..46..655T. doi:10.1016/S0094-5765(00)00028-X.
- Galántai, Z. "Long Futures and Type IV Civilizations". Periodica Polytechnica, Social and Management Sciences 12 (1): 83–89. Retrieved 2009-05-30.
- McInnes, Colin R. (March–April 2005). "Dynamics of a Particle Moving Along an Orbital Tower". Journal of Guidance, Control, and Dynamics 28 (2). Retrieved 2009-05-30.