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A photon rocket is a hypothetical rocket that uses thrust from emitted photons (radiation pressure by emission) for its propulsion. Photons could be generated by onboard generators, as in the nuclear photonic rocket. The standard textbook case of such a rocket is the ideal case where all of the fuel is converted to photons which are radiated in the same direction. In more realistic treatments, one takes into account that the beam of photons is not perfectly collimated, that not all of the fuel is converted to photons, and so on. A large amount of fuel would be required and the rocket would be a huge vessel.〔(A Photon Rocket, by G.G. Zel'kin )〕〔(There will be no photon rocket, by V. Smilga )〕 In the ''Beamed Laser Propulsion'', the photon generators and the spacecraft are physically separated and the photons are beamed from the photon source to the spacecraft using lasers. In the Photonic Laser Thruster, collimated photons are reused by mirrors, multiplying the force by the number of bounces. ==Speed== The speed an ideal photon rocket will reach, in the absence of external forces, depends on the ratio of its initial and final mass: : where is the initial mass and is the final mass. The gamma factor corresponding to this speed has the simple expression: : 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「photon rocket」の詳細全文を読む スポンサード リンク
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