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Electric Propulsion (EP) or Plasma Propulsion (PP): The acceleration of gases for the
purpose of producing propulsive thrust by electric heating, electric body forces, and/or
electric and magnetic body forces.
For satellite or deep-space missions utilizing chemical propulsion, a large percentage
of the spacecraft wet mass is propellant. Due to vehicle mass and cost design constraints,
this excessive amount of propellant decreases the mass available for payload. In some
cases, the mass available for the payload is so small that the mission is no longer feasible
within the design space.
Studies have shown that ideally, an engine which would be used as the primary source of
propulsion for orbit transfer missions or for satellite station-keeping should produce
exhaust velocities between 10-20 km/s. Cryogenic chemical rocket systems (e.g., the Space
Shuttle Main Engines) are capable of producing exhaust velocities approaching 5 km/s and
storable chemical systems that are currently in use for spacecraft propulsion have
significantly lower performance still. It is apparent that a propulsion system is
required that does not rely on energy addition through chemical reactions.
Electric Propulsion (EP) thrusters are such a design enabling technology, producing
exhaust velocities on the order of 10-20 km/s (much larger velocities are
possible). This significantly decreases propellant
mass and typically increases payload. Drawbacks of EP are low thruster
(compared to chemical rockets) and large
power supply mass. In some cases, the mass of the power supply offsets the gains of
choosing EP over chemical systems. However, recent advances in both EP and power supply
technology are making these systems viable options for energetic deep-space missions,
attitude control, and near-Earth orbit raising missions just to name a few.
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EP is logically classified into three categories: