||This article needs additional citations for verification. (June 2010)|
A clanking replicator is an artificial self-replicating system that relies on conventional large-scale technology and automation. The term evolved to distinguish such systems from the microscopic "assemblers" that nanotechnology may make possible. They are also sometimes called "Auxons", from the Greek word auxein which means "to grow", or "von Neumann machines" after John von Neumann, who first rigorously studied the idea. This last term ("von Neumann machine") is less specific and also refers to a completely unrelated computer architecture proposed by von Neumann, so its use is discouraged where accuracy is important. A related concept is the Von Neumann universal constructor.
The term clanking replicator was used by Drexler, is informal and is rarely used by others in popular or technical discussions.
Basic concept 
A self-replicating machine would need to have the capacity to gather energy and raw materials, process the raw materials into finished components, and then assemble them into a copy of itself. It is unlikely that this would all be contained within a single monolithic structure, but would rather be a group of cooperating machines or an automated factory that is capable of manufacturing all of the machines that make it up. The factory could produce mining robots to collect raw materials, construction robots to put new machines together, and repair robots to maintain itself against wear and tear, all without human intervention or direction. The advantage of such a system lies in its ability to expand its own capacity rapidly and without additional human effort; in essence, the initial investment required to construct the first clanking replicator would have an arbitrarily large payoff with no additional labor cost, with future returns discounted by their present value.
Noting another proof that self-replicating machines are possible is the simple fact that all living organisms are self replicating by definition.
History of the concept 
The idea of non-biological self-replicating systems was introduced in Samuel Butler's article "Darwin Among the Machines" published only a few years after The Origin of Species. As a serious proposal, it was first suggested by mathematician John Von Neumann in the late 1940s when he proposed a kinematic self-reproducing automaton model as a thought experiment. See Von Neumann, J., 1966, The Theory of Self-reproducing Automata, A. Burks, ed., Univ. of Illinois Press, Urbana, IL.
Advanced Automation for Space Missions 
In 1980, NASA conducted a summer study entitled Advanced Automation for Space Missions, edited by Robert Freitas, to produce a detailed proposal for self-replicating factories to develop lunar resources without requiring additional launches or human workers on-site. The proposed system would have been capable of exponentially increasing productive capacity. The design could be modified to build Von Neumann probes to explore the galaxy.
The reference design specified small computer-controlled electric carts running on rails. Each cart could have a simple hand or a small bulldozer shovel, forming a basic robot.
Power would be provided by a "canopy" of solar cells supported on pillars. The other machinery could run under the canopy.
The study identified four key manufacturing capabilities out of the hundreds commonly used in modern industry:
- Plaster casting for molded parts
- Laser machining for etching and fine tuning
- Vapor deposition for electronics, solar cells, and mirror surfaces
- Extrusion of spun basalt fiber for electrical insulation and fiberglass
A "casting robot" would use a robotic arm with a few sculpting tools to make plaster molds. Plaster molds are easy to make, and can make precise parts with good surface finishes. The robot would then cast most of the parts either from nonconductive molten rock (basalt) or purified metals. An electric or solar oven would melt the materials. A carbon dioxide laser cutting and welding system was also included.
A more speculative, more complex "chip factory" was specified to produce the computer and electronic systems, but the designers also said that it might prove practical to ship the chips from Earth as if they were "vitamins."
Much of the design study was concerned with a simple, flexible chemical system for processing the ores, and the differences between the ratio of elements needed by the replicator, and the ratios available in lunar regolith. The element that most limited the growth rate was chlorine, needed to process regolith for aluminium. Chlorine is very rare in lunar regolith, so the design recycled it.
Other references 
- Freeman Dyson expanded upon Neumann's automata theories, and advanced a biotechnology-inspired theory. See Astrochicken.
- The first technical design study of a self-replicating interstellar probe was published in a 1980 paper by Robert Freitas
- Clanking replicators are also mentioned briefly in the fourth chapter of K. Eric Drexler's 1986 book Engines of Creation.
- Article about a proposed clanking replicator system to be used for developing Earthly deserts in the October 1995 Discover Magazine, featuring forests of solar panels that powered desalination equipment to irrigate the land.
- In 1995, Nick Szabo proposed a challenge to build a macroscale replicator from Lego(tm) robot kits and similar basic parts. Szabo wrote that this approach was easier than previous proposals for macroscale replicators, but successfully predicted that even this method would not lead to a macroscale replicator within ten years.
- In 1998, Chris Phoenix suggested a general idea for a macroscale replicator on the sci.nanotech newsgroup, operating in a pool of ultraviolet-cured liquid plastic, selectively solidifying the plastic to form solid parts. Computation could be done by fluidic logic. Power for the process could be supplied by a pressurized source of the liquid.
- In 2001, Peter Ward mentioned an escaped clanking replicator destroying the human race in his book Future Evolution.
- In 2004, General Dynamics completed a study for NASA's Institute for Advanced Concepts. It concluded that complexity of the development was equal to that of a Pentium 4, and promoted a design based on cellular automata.
- In 2004, Robert Freitas and Ralph Merkle published the first comprehensive review of the field of self-replication, in their book Kinematic Self-Replicating Machines, which includes 3000+ literature references.
- In 2005, Adrian Bowyer of the University of Bath started the RepRap project to develop a rapid prototyping machine which would be able to replicate itself, making such machines cheap enough for people to buy and use in their homes. The project is releasing material under the GNU GPL. 
Clanking replicators in fiction 
An early treatment was the short story "Autofac" by Philip K. Dick, published in 1955, which precedes von Neumann's original paper about self-reproducing machines. Another example can be found in the 1962 short story "Epilogue" by Poul Anderson, in which self-replicating factory barges were proposed that used minerals extracted from ocean water as raw materials.
In his short story "Crabs on the Island" (1958) Anatoli Dneprov speculated on the idea that since the replication process is never 100% accurate, leading to slight differences in the descendants, over several generations of replication the machines would be subjected to evolution similar to that of living organisms. In the story, a machine is designed, the sole purpose of which is to find metal to produce copies of itself, intended to be used as a weapon against an enemy's war machines. The machines are released on a deserted island, the idea being that once the available metal is all used and they start fighting each other, natural selection will enhance their design. However, the evolution has stopped by itself when the last descendant, an enormously large crab, was created, being unable to reproduce itself due to lack of energy and materials.
Stanisław Lem has also studied the same idea in his novel The Invincible (1964), in which the crew of a spacecraft landing on a distant planet finds non-biological life-form, which is the product of long, possibly of millions of years of mechanical evolution. This phenomenon is also key to the aforementioned Anderson story.
John Sladek used the concept to humorous ends in his first novel The Reproductive System (1968, also titled Mechasm in some markets), where a U.S. military research project goes out of control.
The second season of the TV-series Lexx features the villain Mantrid, who has decided to convert all matter in space into robot drones.
Replicators as Weapons 
A concept that has become well used in fiction is the use of such replicators as weapons. In written fiction, A. E. van Vogt used the idea as a plot device in his story "M33 in Andromeda" (1943), which was later combined with the three other Space Beagle stories to became the novel, The Voyage of the Space Beagle. The story describes the creation of self-replicating weapons factories designed to destroy the Anabis, a galaxy-spanning malevolent life form bent on destruction of the human race. Philip K. Dick also touched on this theme in his 1953 short story "Second Variety" (slightly predating "Autofac," mentioned earlier). The concept of self-replicating weapon robots was explored at great length in the Berserker series of books and short stories by Fred Saberhagen, starting in 1963, which also served as the basis of the Star Trek episode "The Doomsday Machine".
In Hollywood, the movie Screamers, based on Dick's short story "Second Variety," features a group of robot weapons created by mankind to act as Von Neumann devices / berserkers. The original robots are subterranean buzzsaws that make a screaming sound as they approach a potential victim beneath the soil. These machines are self-replicating and, as is found out through the course of the movie, they are quite intelligent and have managed to "evolve" into newer, more dangerous forms, most notably human forms which the real humans in the movie cannot tell apart from other real humans except by trial and error. The popular TV series Stargate SG-1 introduces 'Replicators' as some of the deadliest enemies of life.
Other notable fiction literature containing clanking replicators 
- The Forge of God by Greg Bear
- 2010: Odyssey Two by Arthur C. Clarke
- The World at the End of Time by Frederik Pohl
- Recursion by Tony Ballantyne ISBN 0-330-42699-0
- Evolution by Stephen Baxter
Prospects for implementation 
As the use of industrial automation has expanded over time, some factories have begun to approach a semblance of self-sufficiency that is suggestive of clanking replicators. However, such factories are unlikely to achieve "full closure" until the cost and flexibility of automated machinery comes close to that of human labour and the manufacture of spare parts and other components locally becomes more economical than transporting them from elsewhere. Fully capable machine replicators are most useful for developing resources in dangerous environments which are not easily reached by existing transportation systems (such as outer space).
A clanking replicator can be considered to be a form of artificial life. Depending on its design, it might be subject to evolution over long time periods. However, with robust error correction, and the possibility of external intervention, the common science fiction theme of robotic life run amok is unlikely in the near term.
It should probably be noted that clanking is an example of onomatopoeia, understandable to some English speakers, but not to all. The term is meant to evoke the image of a nineteenth century factory, powered by steam, pushing gears and rods, noisy and clamorous.
- Drexler, K. Eric (1986). "Engines of Abundance (Chapter 4) Clanking Replicators". Engines of Creation.