thumb|Inventor Norman L. Dean beside one of his "Dean drive" apparatuses.
The Dean drive was a device created and promoted by inventor Norman Lorimer Dean (1902–1972) that he claimed to be a reactionless drive. Dean claimed that his device was able to generate a uni-directional force in free space, in violation of Newton's third law of motion from classical physics. His claims generated notoriety because, if true, such a device would have had enormous applications, completely changing human transport, engineering, space travel and more. Dean made several controlled private demonstrations of a number of different devices; however, no working models were ever demonstrated publicly or subjected to independent analysis and Dean never presented any rigorous theoretical basis for their operation. Analysts conclude that the motion seen in Dean's device demonstrations was likely reliant on asymmetrical frictional resistance between the device and the surface on which the device was set ("stick and slip"), resulting in the device moving in one direction when in operation, driven by the vibrations of the apparatus.
Early publicity
The Dean drive obtained a good deal of publicity in the 1950s and 1960s via the columns and conference presentations of John W. Campbell, the longtime editor of Astounding Science Fiction magazine. At that time, Campbell believed that his magazine had to change society by helping breakthrough research that was rejected by "mainstream" science, and he promoted a series of far-reaching ideas that had dubious scientific bases, like Dianetics, dowsing, the Hieronymus machine, and the Dean drive. Campbell believed that the device worked and claimed to have witnessed it operating on a bathroom scale. The weight reading on the scale appeared to decrease when the device was activated. He subsequently published photographs of the scale with the drive stopped and running. The June 1960 cover of Astounding magazine featured a painting of a United States submarine near Mars, supposedly propelled there by a Dean drive.
Dean, who was trying to find potential buyers for his technology, was secretive about the details of how it was supposed to work, but it was said to contain asymmetrical rotating weights and to generate a great deal of vibration.
Dean and Campbell claimed that Newton's laws of motion were only an approximation, and that Dean had discovered a fourth law of motion. This has been described as a nonlinear correction to one of Newton's laws, which, if correct, would allegedly have rendered a reactionless drive feasible after all.
One result of the initial articles in Campbell's magazine was that two other researchers, William O. Davis and G. Harry Stine, visited Dean and witnessed a demonstration. Results of this visit were published in the May 1962 and June 1976 issues of the magazine, the name of which had been changed by Campbell from Astounding to Analog. Davis witnessed a demonstration by Dean, and wrote: "It was the conclusion of both Harry Stine and myself that we had witnessed a real anomaly and that the possibility of fraud in the demonstration was slim."
Purported weight loss
Dean made a demonstration for a representative of the magazine Popular Mechanics of one of his "Dean drive" devices. The witness reported that "While suspended above the ground, was able to pull a load to itself without itself being pulled toward the load".
Later analysis has revealed that the interactions of vibration, friction, and resonance with the springs of the scale are likely the root cause of the apparent weight loss reported by Campbell and others of apparent "anti-gravity" and "reactionless thruster" effects.
Patents
Dean was granted two U.S. patents on mechanical devices presumably related to his Dean drive claims. His first patent for a "System for converting rotary motion into unidirectional motion" was granted on May 9, 1959. Another patent for a "Variable oscillator system" was granted on May 11, 1965. These two patent designs were the only ones where Dean revealed the design details with an explanation for operation. However, the details were incomplete, and it is not possible to build a Dean drive just from the explanations in the patent.
Dean's patented devices, and his explanation of how his drive was supposed to work, were later shown to develop no net weight loss over time and do not violate Newton's third law of motion. Many other inventors claim to have invented similar devices, and they all still remain unproven, and lacking a solid theoretic basis.