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Advanced Space Propulsion Laboratory

VARIABLE SPECIFIC IMPULSE MAGNETOPLASMA ROCKET

The VASIMR system encompasses three linked magnetic cells, consisting of a “plasma source,” an “RF booster,” and a “magnetic nozzle.” With this configuration, plasma can be guided and controlled over a wide range of temperatures and densities.

IMAGE: Rocket Concept DiagramThe plasma source cell involves the main injection of neutral gas (typically hydrogen, or other light gases) to be turned into plasma and the ionization subsystem. The RF booster cell acts as an amplifier to further energize the plasma to the desired temperature using electromagnetic waves. The magnetic nozzle cell converts the energy of the plasma into directed motion and ultimately useful thrust.

The key to plasma rocket operation is its capability to vary or “modulate” the plasma exhaust while maintaining maximum power. This technique works like the function of the transmission in a conventional automobile.

Two parameters are varied during a typical operation: thrust and the velocity of the particles leaving at the rocket exhaust. This latter is called the specific impulse. As the ship accelerates on its journey, the thrust decreases and the specific impulse increases. The opposite is also true as the ship slows down at its destination.

Important Technology

  • Super conducting magnets at space temperatures.
  • Compact power generation and conditioning equipment.
  • Compact and robust radio frequency systems.
  • Hybrid magnetic nozzle.
  • Light weight heat shields and radiative cooling.
Range of Parameters

IMAGE: Range of Parameters
The chart depicts the dependence of the rocket thrust and propellant rate on the exhaust speed for the Mars mission vehicle with 10 megawatt power.

Note: In the metric system of units, rocket thrust is measured in Newtons (1 Newton is about 1/4 pound).

Advantages
*Variable Specific Impulse and Thrust at maximum power.
*Electrodeless design with magnetic insulation.
*High power density.
*Continuous acceleration (very low artificial gravity).
*High efficiency Ion Cyclotron Resonance Heating, high voltage and low current.
*Capability for powered mission aborts.
*Propulsion system is adaptable to slow, high payload robotic cargo missions as well as fast, lower payload human transfers.

Curator: Kim Dismukes | Responsible NASA Official: John Ira Petty | Updated: 04/16/2004
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