Electric propulsion is a form of
spacecraft propulsion used in
outer
space. This type of rocket-like
reaction engine utilize
electric energy to obtain thrust from propellant carried with the vehicle.
Unlike rocket engines these kinds of engines do not necessarily have
rocket nozzles, and thus many types are not considered true
rockets.
While electric thrusters typically offer much higher
specific impulse, due to electrical power constraints thrust is weaker
compared to chemical thrusters by several
orders of magnitude.
The idea of electric propulsion dates back to
1906, when
Robert Goddard considered the possibility in his personal notebook.
Konstantin Tsiolkovsky published the idea in
1911.
Types of electric propulsion
The various technologies of electric propulsion for spacecraft are usually
grouped in three families based on the type of force used to accelerate the ions
of the plasma.
Electric propulsion systems can also be characterized in terms of their
operation in either steady (continuous firing for a prescribed duration) or
unsteady (pulsed firings accumulating to a desired thrust bit).
Electrostatic
If the acceleration is caused mainly by the
Coulomb Force (i.e application of a static
electric field in the direction of the acceleration) the device is
considered electrostatic.
-
Ion
thruster
-
Hall effect thruster
-
Field Emission Electric Propulsion
-
Colloid thruster
Electrothermal
The electrothermal category groups the devices where electromagnetic fields
are used to generate a
plasma to
increase the heat
of the bulk propellant. The thermal energy imparted to the propellant gas is
then converted into kinetic energy by a
nozzle of
either physical material construction or by magnetic means. Low molecular weight
gases are preferred propellants (e.g. hydrogen, helium, ammonia) for this kind
of system.
Performance of electrothermal systems in terms of specific impulse (Isp) is
somewhat modest (500 to ~1000 seconds), but exceeds that of
cold gas thrusters,
monopropellant thrusters, and even most
bi-propellant thrusters. In the
USSR electrothermal engines were used since 1971,
Soviet
"Meteor-3", "Meteor-Priroda", "Resurs-O" satellite series and
Russian "Elektro"
satellite are equipped with them.
Electrothermal systems by
Aerojet
(MR-510) are currently used on
Lockheed-Martin A2100 satellites using
hydrazine
as a propellant.
-
DC arcjet
-
microwave arcjet
-
VASIMR
Electromagnetic
If the ions are accelerated either by the
Lorentz Force or by the effect of an electromagnetic fields where the
electric field is not in the direction of the acceleration, the device is
considered electromagnetic.
-
MPD thruster
-
Electrodeless plasma thruster
-
Pulsed inductive thruster
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