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Fundamentals of
Electric Propulsion
Ion and Hall Thrusters
Dan M. Goebel
Ira Katz
Jet Propulsion Laboratory
California Institute of Technology
Electric propulsion is a technology aimed at achieving thrust with high exhaust
velocities, which results in a reduction in the amount of propellant required for
a given space mission or application compared to other conventional propulsion
methods. Reduced propellant mass can significantly decrease the launch mass
of a spacecraft or satellite, leading to lower costs from the use of smaller launch
vehicles to deliver a desired mass into a given orbit or to a deep-space target.
In general, electric propulsion (EP) encompasses any propulsion technology in
which electricity is used to increase the propellant exhaust velocity. There are
many figures of merit for electric thrusters, but mission and application
planners are primarily interested in thrust, specific impulse, and total efficiency
in relating the performance of the thruster to the delivered mass and change in
the spacecraft velocity during thrust periods. While thrust is self-explanatory,
specific impulse (Isp) is defined as the propellant exhaust velocity divided by
the gravitational acceleration constant g, which results in the unusual units of
seconds. The total efficiency is the jet power produced by the thrust beam
divided by the electrical power into the system. Naturally, spacecraft designers
are then concerned with providing the electrical power that the thruster requires
to produce a given thrust, as well as with dissipating the thermal power that the
thruster generates as waste h
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