- Electric propulsion
Electric propulsion is a form of
spacecraft propulsionused in outer space. This type of rocket-like reaction engineutilize electric energyto 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.cite web |url=http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=34201&fbodylongid=1535 |title=Electric versus Chemical Propulsion |work=Electric Spacecraft Propulsion |publisher= ESA|accessdate=2007-02-17 ] Russian satellites have used electric propulsion for decades, and newer Western geo-orbiting spacecraft are starting to use them for north-south stationkeeping.
The idea of electric propulsion dates back to 1906, when Robert Goddard considered the possibility in his personal notebook.cite journal
last = Choueiri
first = Edgar Y.
year = 2004
title = A Critical History of Electric Propulsion: The First 50 Years (1906–1956)
journal = Journal of Propulsion and Power
volume = 20
issue = 2
pages = 193–203
url = http://alfven.princeton.edu/papers/choueiriJPP04aabstext.htm
doi = 10.2514/1.9245 ]
Konstantin Tsiolkovskypublished 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).
If the acceleration is caused mainly by the
Coulomb Force(i.e application of a static electric fieldin the direction of the acceleration) the device is considered electrostatic.
Electrostatic ion thruster
Field Emission Electric Propulsion
The electrothermal category groups the devices where electromagnetic fields are used to generate a
plasmato increase the heatof the bulk propellant. The thermal energy imparted to the propellant gas is then converted into kinetic energy by a nozzleof 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 USSRelectrothermal engines were used since 1971, Soviet "Meteor-3", "Meteor-Priroda", "Resurs-O" satellite series and Russian "Elektro" satellite are equipped with them. [ru icon [http://www.novosti-kosmonavtiki.ru/content/numbers/198/35.shtml Native Electric Propulsion Engines Today] , Novosti Kosmonavtiki, 1999, No.7] Electrothermal systems by Aerojet(MR-510) are currently used on Lockheed-MartinA2100 satellites using hydrazineas a propellant.
If the ions are accelerated either by the
Lorentz Forceor by the effect of an electromagnetic fields where the electric field is not in the direction of the acceleration, the device is considered electromagnetic.
Electrodeless plasma thruster
Hall effect thruster
Pulsed inductive thruster
Vacuum arc thruster
Battery electric vehicle
*Aerospace America, AIAA publication, December 2005, Propulsion and Energy section, pp.54-55, written by Mitchell Walker.
* [http://www.pwrengineering.com/dataresources/Lazarovici_paper.pdf Distributed Power Architecture for Electric Propulsion]
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