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reactionless drive (Not to be confused with Field propulsion. 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 that is a closed system, presumably in contradiction with the law of conservation of momentum. Reactionless drives are often considered similar to a perpetual motion machine. The name comes from Newton's third law, often expressed as, "for every action, there is an equal and opposite reaction." A large number of infeasible reactionless drives, such as the Dean drive, are a staple of science fiction particularly for space propulsion. AllaR) |
