Magnetics Business & Technology - Summer 2018 - 13

SPECIAL REPORT: AEROSPACE & DEFENSE

Dual Thrusters Combine Benefits of Ion
Thrusters and Hall Eﬀect Thrusters for
Electric Propulsion
Two different types of electrostatic thrusters are used to propel
spacecraft: ion thrusters and Hall effect thrusters. Ion thrusters
have the benefit of relatively high exhaust velocities with higher
overall thrust efficiencies. Hall effect thrusters typically offer
higher thrust-to-power ratios, but they operate somewhat less
efficiently than ion thrusters do.
To take advantage of both thrusters strengths, scientists and engineers at NASA's Glenn Research Center have developed what
is essentially a dual thruster propulsion system. This patented
electric propulsion device offers the ability to switch a spacecraft's propulsion system to ion-thruster mode or Hall-thruster
mode depending on whether the principal need is efficiency or
thrust power. In addition, Glenn's technology allows the dual
thruster to operate in burst mode, with one thruster acting as
an ion thruster and one as a Hall thruster. This capability can
be valuable to facilitate smooth transitions between operating
modes or to raise total thrust level for short periods beyond what
either mode can achieve on its own.

How it works
Ion thrusters and Hall effect thrusters both generate beams of
ions to create thrust. The ion thruster uses two or three multiaperture grids, in which the ions are accelerated due to the

difference in potential between the first (screen) and second
(accelerator) grids.
Like the ion thruster, the Hall effect thruster creates thrust by
ionizing propellant within an electric field, but instead of a grid
the Hall thruster has an electron plasma at the open end of the
thruster. Because of the counter-flowing electron and ion currents in the Hall effect thruster channel, a greater ion flux can be
achieved compared to the ion thruster. For this reason, the Hall
thruster yields a higher thrust-to-power ratio, whereas the ion
thruster can produce higher exhaust velocities with higher overall
thrust efficiencies.
The dual-thruster design has several noteworthy advantages.
Having the neutralizer cathode assembly (NCA) in a central position eliminates the cantilevered-outboard NCA that most conventional ion thrusters use. In addition, the ion optics allow the
ion thrusters to be scaled to very high power by permitting very
large beam areas with relatively small electrode spans. These
flat ion optics electrodes also improve thrust-to-power ratios and
efficiencies compared to more conventional, spherically domed
electrodes. Finally, the increased anode-surface area for electron
collection means that the engine can operate at higher discharge
currents and therefore higher input power levels. All of these
advantages add up to an electric propulsion device that combines the efficiencies of an ion thruster with the thrust-to-power
capacity of a Hall effect thruster.
For more info, visit https://www.NASA.gov

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Summer 2018 * Magnetics Business & Technology

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