Em Drive

Em Drive

EmDrive (also Relativity Drive) is the name of a spacecraft propulsion system proposed, and reportedly developed, by Roger Shawyer. New Scientist ran a cover story on EmDrive in its 8 September 2006 issue. The device is a magnetron with a specially shaped, fully enclosed tapering resonator cavity whose area is greater at one end. The inventor claims that the device generates thrust even though no detectable energy leaves the device. The inventor proposes to use it as a spacecraft propulsion system that uses no fuel (other than electricity), and no reaction mass.

On his homepage the inventor claims that independent peer-review is under way. In the November 5, 2012 edition of Aviation Week and Space Technology, it is reported that Chinese researchers have validated the EmDrive technology, and created a working device. An English translation of the peer reviewed article is available from the inventor's website. Yang Juan, professor of propulsion theory and engineering of aeronautics and astronautics at the Northwestern Polytechnic University in Xian, claims in a peer reviewed journal to have built a model that produces 0.72 Newtons (0.16 lb.) of thrust from 2.5 kW of input power. By comparison, the NASA HiPEP ion thruster, intended for use on the JIMO mission but never deployed, requires 25-50 kW of power, delivers 0.46-0.67 Newtons of thrust, and relies on Xenon gas as a reaction mass. When the Xenon gas is depleted, the thruster ceases to function. It is claimed that the EmDrive, because it does not rely on reaction mass, would work indefinitely without any fuel other than electricity. Because the reaction mass typically forms 90% or more of the total weight of a spacecraft, a thruster that did not require reaction mass would represent a fundamental breakthrough in spacecraft design and propulsion.

Despite Chinese confirmation, the device's operation as described seemingly violates several basic laws of physics; notably conservation of momentum, though the inventor insists to the contrary. John Costella, an expert in relativistic electrodynamics describes the EmDrive as a 'fraud'. The Chinese results are a matter of significant debate within the Aerospace community, and are considered quite controversial. At the time of this edit (November 2012) it is unclear whether the EmDrive represents a fundamental breakthrough, or a fundamental mistake.

Read more about Em Drive:  Principle of Operation, Criticism, Prototypes and Tests, New Scientist Article, Analysis, Chinese Interest

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