Reactionless drive

A reactionless drive is a device producing motion without the exhaust of a propellant. A propellantless drive is not necessarily reactionless when it constitutes an open system interacting with external fields; but a reactionless drive is a particular case of a propellantless drive as it is a closed system presumably in contradiction with the law of conservation of momentum and often considered similar to a perpetual motion machine. The name comes from Newton's third law, which is usually expressed as, "for every action, there is an equal and opposite reaction." A large number of infeasible devices, such as the Dean drive, are a staple of science fiction particularly for space propulsion. To date, no reactionless device has ever been validated under properly controlled conditions.

Through the years there have been numerous claims for functional reactionless drive designs using ordinary mechanics (i.e. devices not said to be based on quantum mechanics, relativity or atomic forces or effects). Two of these represent their general classes: The "Dean drive" is perhaps the best known example of a "linear oscillating mechanism" reactionless drive; The "GIT" is perhaps the best known example of a "rotating mechanism" reactionless drive. These two also stand out as they both received much publicity from their promoters and the popular press in their day and both were eventually rejected when proven to not produce any reactionless drive forces. The rise and fall of these devices now serves as a cautionary tale for those making and reviewing similar claims.

The Dean drive was a mechanical device concept promoted by inventor Norman L. Dean. Dean claimed that his device was a "reactionless thruster" and that his working models could demonstrate this effect. He held several private demonstrations but never revealed the exact design of the models nor allowed independent analysis of them. Dean's claims of reactionless thrust generation were subsequently shown to be in error and the "thrust" producing the directional motion was likely to be caused by friction between the device and the surface on which the device was resting and would not work in free space.

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