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The Variable Specific Impulse Magnetoplasma Rocket (VASIMR) is an electromagnetic thruster for spacecraft propulsion. It uses radio waves to ionize and heat a propellant, and magnetic fields to accelerate the resulting plasma to generate thrust. It is one of several types of spacecraft electric propulsion systems. The method of heating plasma used in VASIMR was originally developed as a result of research into nuclear fusion. VASIMR is intended to bridge the gap between high-thrust, low-specific impulse propulsion systems and low-thrust, high-specific impulse systems. VASIMR is capable of functioning in either mode. Costa Rican–born American scientist and former NASA astronaut Franklin Chang Díaz created the VASIMR concept and has been working on its development since 1977. VASIMRs units for development and test have been assembled by the Ad Astra Rocket Company, headquartered in the city of Houston, Texas, United States.〔(【引用サイトリンク】url=http://www.adastrarocket.com/aarc/about-us )〕 == Design and operation == The Variable Specific Impulse Magnetoplasma Rocket, sometimes referred to as the Electro-thermal Plasma Thruster or Electro-thermal Magnetoplasma Rocket, uses radio waves to ionize and heat propellant, which generates plasma that is accelerated using magnetic fields to generate thrust. This type of engine is electrodeless and as such belongs to the same electric propulsion family (while differing in the method of plasma acceleration) as the electrodeless plasma thruster, the microwave arcjet, or the pulsed inductive thruster class. It can also be seen as an electrodeless version of an arcjet, able to reach higher propellant temperature by limiting the heat flux from the plasma to the structure. Neither type of engine has any electrodes. This is advantageous in that it eliminates problems with electrode erosion that cause rival designs of ion thrusters to have relatively shorter life expectancy. Furthermore, since every part of a VASIMR engine is magnetically shielded and does not come into direct contact with plasma, the potential durability of this engine design is greater than other ion/plasma engine designs.〔 VASIMR can be most basically thought of as a convergent-divergent nozzle for ions and electrons. The propellant (a neutral gas such as argon or xenon) is first injected into a hollow cylinder surfaced with electromagnets. Upon entry into the engine, the gas is first heated to a “cold plasma” by a helicon RF antenna (also known as a “coupler”) which bombards the gas with electromagnetic waves, stripping electrons off the argon or xenon atoms and leaving plasma consisting of ions and loose electrons to continue down the engine compartment. By varying the amount of energy dedicated to RF heating and the amount of propellant delivered for plasma generation VASIMR is capable of generating either low-thrust, high–specific impulse exhaust or relatively high-thrust, low–specific impulse exhaust. The second phase is a strong electromagnet positioned to compress the ionized plasma in a similar fashion to a convergent-divergent nozzle that compresses gas in traditional rocket engines. A second coupler, known as the Ion Cyclotron Heating (ICH) section, emits electromagnetic waves in resonance with the orbits of ions and electrons as they travel through the engine. Resonance of the waves and plasma is achieved through a reduction of the magnetic field in this portion of the engine which slows down the orbital motion of the plasma particles. This section further heats the plasma to temperatures upwards of 1,000,000 kelvin—about 173 times the temperature of the Sun’s surface. Motion of ions and electrons through the engine can be approximated by lines parallel to the engine walls; however, the particles actually orbit those lines at the same time that they are traveling linearly through the engine. The final, diverging, section of the engine contains a steadily expanding magnetic field which forces the ions and electrons into steadily lengthening spiral orbits in order to eject from the engine parallel and opposite to the direction of motion at speeds of up to 50,000 m/s, propelling the rocket forward through space.〔 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「Variable Specific Impulse Magnetoplasma Rocket」の詳細全文を読む スポンサード リンク
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