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. The main advantage of such designs is elimination of problems with electrode erosion that cause rival designs of ion thrusters which use electrodes to have a short 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.
The engine design encompasses three parts: turning gas into plasma via helicon RF antennas; energizing plasma via further RF heating in an ion cyclotron resonance frequency (ICRF) booster; and using electromagnets to create a magnetic nozzle to convert the plasma's built-up thermal energy into kinetic force. By varying the amount of energy dedicated to RF heating and the amount of propellant delivered for plasma generation VASIMR is capable of either generating low-thrust, high-specific impulse exhaust or relatively high-thrust, low-specific impulse exhaust.
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