Electric propulsion

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.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 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.

*Electrostatic ion 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. [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-Martin A2100 satellites using hydrazine as a propellant.

*DC arcjet
*microwave arcjet
*Pulsed plasma thruster
*Helicon Double Layer Thruster

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.

*Electrodeless plasma thruster
*Hall effect thruster
*MPD thruster
*Pulsed inductive thruster
*VASIMR

Other

*Vacuum arc thruster

Energy efficiency

See also

* Battery electric vehicle

References

*Aerospace America, AIAA publication, December 2005, Propulsion and Energy section, pp.54-55, written by Mitchell Walker.

External links

* [http://www.pwrengineering.com/dataresources/Lazarovici_paper.pdf Distributed Power Architecture for Electric Propulsion]
*http://www.daviddarling.info/encyclopedia/E/electricprop.html
*http://www.nasa.gov/offices/oce/llis/0736.html