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A radio frequency (RF) resonant cavity thruster is a proposed new type of electromagnetic thruster. Unlike conventional electromagnetic thrusters, they are designed to use no reaction mass, and to emit no directional radiation. Their design principles are not supported by prevailing scientific theories, and they apparently violate the law of conservation of momentum.〔 〕 A few variations on such thrusters have been proposed. Aerospace engineer Roger Shawyer designed the EmDrive in 2001, and has persistently promoted the idea since then through his company, Satellite Propulsion Research. Chemical engineer Guido Fetta designed the Cannae Drive, based on similar principles. If they were found to work as claimed, providing thrust without consuming a propellant would have important applications to all areas of propulsion, from spacecraft〔〔〔〔 to other vehicles.〔 A few independent teams of physicists, notably a team at Xi'an's Northwestern Polytechnical University (NWPU), one at NASA's Eagleworks laboratories, and another at the Dresden University of Technology in Germany,〔 have built prototypes of these designs. While some of their experiments have observed a small net thrust from those prototypes,〔 others have criticised their results.〔 This experimental work has been published in university journals,〔 conference proceedings,〔〔 and some local Chinese peer-reviewed journals.〔〔〔 Research is in progress to see if these effects are caused by some as-yet-unknown phenomenon, or artifacts due to experimental error, particularly because the observed results are small, and there are otherwise no compelling explanations for its operation principle. Claims of such a surprising result would need especially thorough evidence to convince the scientific community and rule out sources of error. == History == Electromagnetic propulsion designs have been around since the start of the 20th century, which operate on the principle of reaction mass. In the 1960s, extensive research was conducted on a variety of such drives: from ion thrusters that strip ions from propellant, accelerate them, and eject them; to plasma thrusters that eject plasma ions in a similar way with plasma currents, but do not require electrodes. The plasma in a plasma thruster can be generated from an intense source of microwave or other radio-frequency (RF) energy, in combination with a resonant cavity tuned to resonate at such a frequency. Searching for low-propellant space drives has been a goal of space exploration for much of this time. If a zero-propellant drive existed, it could potentially be used for travel in many environments. This has contributed to the enthusiasm for exploring such designs, even if they seem impossible. Since the publication of Isaac Newton's book Principia science has understood that for every action there is an equal and opposite reaction. General Relativity of Albert Einstein did not change the principle that came to be known as conservation of momentum. Newton built his theories based on earlier work of Galileo, Copernicus, and Kepler. The principle requires that to create thrust force in one direction, some form of energy must be repelled at some speed in the opposite direction sufficient to balance the momentum around any closed surface that might be constructed to measure it. Reaction forces can be produced by accelerated mass like a conventional rocket, interaction with external electric or magnetic fields like the separate parts of an electric motor, particle beams like ion thrusters, or directional radio waves. Nozzle velocity is a key parameter in rockets. If no mass is ejected the exhaust energy moves at light speed and requires F = P/c or about 300 megawatts per newton of force, making it less attractive than other propulsion systems. The patent of Roger J. Shawyer claims the thrust is generated in a closed cavity such that one end of the cavity receives a larger force than the opposite end. Electric heat turns liquid coolant into vapor, contributing to the force balance. A standing wave interference pattern is created by geometry, operating frequency and equal path lengths for all segments of the microwave. Stress energy of space is altered inside the microwave cavity by addition of the interference pattern in which nearly all of the electric and magnetic components are canceled out by two microwaves approaching each other with equal intensity on the same path. Most of the Poynting vectors are also canceled out. Puthoff's patent〔(【引用サイトリンク】url=http://worldwide.espacenet.com/publicationDetails/originalDocument?CC=US&NR=5845220A&KC=A&FT=D&ND=3&date=19981201&DB=EPODOC&locale=en_EP )〕 shows how a small but detectable curl free potential can be created from interference patterns passing through shielded barriers. Otherwise if all of the microwaves remain inside the cavity and there is no net interaction with the vacuum, then there is no established theory to give external thrust to the device. Shawyer's claim〔(【引用サイトリンク】url=http://www.eurekamagazine.co.uk/design-engineering-features/technology/no-propellant-drive-prepares-for-space-and-beyond/9657/ )〕 of 0.1 newton from 300 watts of power is not supported by conventional theories. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「RF resonant cavity thruster」の詳細全文を読む スポンサード リンク
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