Electric propulsion
Encyclopedia
An electrically powered spacecraft propulsion system is any of a number of forms of electric motor
s which spacecraft
can employ to gain mechanical energy in outer space
. Most of these kinds of spacecraft propulsion
work by electrically powering propellant to high speed, but electrodynamic tether
s work by interacting with a planet's magnetosphere.
Electric thrusters typically offer much higher specific impulse
; however, due to practical power source constraints thrust is weaker compared to chemical thrusters by several orders of magnitude. Russia
n satellites have used electric propulsion for decades, and newer Western geo-orbiting spacecraft are starting to use them for north-south stationkeeping.
for spacecraft dates back to 1906, when Robert Goddard considered the possibility in his personal notebook.
Konstantin Tsiolkovsky
published the idea in 1911.
uses 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
.
Electric propulsion thrusters for spacecraft are usually grouped in three families based on the type of force used to accelerate the ions of the plasma:
in the direction of the acceleration) the device is considered electrostatic.
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 solid material or magnetic fields. Low molecular weight gases (e.g. hydrogen, helium, ammonia) are preferred propellants 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 thruster
s, monopropellant rocket
s, and even most bipropellant rockets. In the USSR, electrothermal engines were used since 1971; the Soviet
"Meteor-3
", "Meteor-Priroda", "Resurs-O" satellite series and the Russia
n "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.
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.
, by converting their kinetic energy
to electrical energy, or as motors
, converting electrical energy to kinetic energy. Electric potential is generated across a conductive tether by its motion through the Earth's magnetic field. The choice of the metal conductor
to be used in an electrodynamic tether is determined by a variety of factors. Primary factors usually include high electrical conductivity, and low density
. Secondary factors, depending on the application, include cost, strength, and melting point.
Electric motor
An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...
s which spacecraft
Spacecraft
A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....
can employ to gain mechanical energy in outer space
Outer space
Outer space is the void that exists between celestial bodies, including the Earth. It is not completely empty, but consists of a hard vacuum containing a low density of particles: predominantly a plasma of hydrogen and helium, as well as electromagnetic radiation, magnetic fields, and neutrinos....
. Most of these kinds of spacecraft propulsion
Spacecraft propulsion
Spacecraft propulsion is any method used to accelerate spacecraft and artificial satellites. There are many different methods. Each method has drawbacks and advantages, and spacecraft propulsion is an active area of research. However, most spacecraft today are propelled by forcing a gas from the...
work by electrically powering propellant to high speed, but electrodynamic tether
Electrodynamic tether
Electrodynamic tethers are long conducting wires, such as one deployed from a tether satellite, which can operate on electromagnetic principles as generators, by converting their kinetic energy to electrical energy, or as motors, converting electrical energy to kinetic energy...
s work by interacting with a planet's magnetosphere.
Electric thrusters typically offer much higher specific impulse
Specific impulse
Specific impulse is a way to describe the efficiency of rocket and jet engines. It represents the derivative of the impulse with respect to amount of propellant used, i.e., the thrust divided by the amount of propellant used per unit time. If the "amount" of propellant is given in terms of mass ,...
; however, due to practical power source constraints thrust is weaker compared to chemical thrusters by several orders of magnitude. Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
n satellites have used electric propulsion for decades, and newer Western geo-orbiting spacecraft are starting to use them for north-south stationkeeping.
History
The idea of electric propulsionElectric propulsion
An electrically powered spacecraft propulsion system is any of a number of forms of electric motors which spacecraft can employ to gain mechanical energy in outer space...
for spacecraft dates back to 1906, when Robert Goddard considered the possibility in his personal notebook.
Konstantin Tsiolkovsky
Konstantin Tsiolkovsky
Konstantin Eduardovich Tsiolkovsky was an Imperial Russian and Soviet rocket scientist and pioneer of the astronautic theory. Along with his followers the German Hermann Oberth and the American Robert H. Goddard, he is considered to be one of the founding fathers of rocketry and astronautics...
published the idea in 1911.
Ion/plasma drives
This type of rocket-like reaction engineReaction engine
A reaction engine is an engine or motor which provides propulsion by expelling reaction mass, in accordance with Newton's third law of motion...
uses electric energy to obtain thrust from propellant
Propellant
A propellant is a material that produces pressurized gas that:* can be directed through a nozzle, thereby producing thrust ;...
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
Rocket engine
A rocket engine, or simply "rocket", is a jet engineRocket Propulsion Elements; 7th edition- chapter 1 that uses only propellant mass for forming its high speed propulsive jet. Rocket engines are reaction engines and obtain thrust in accordance with Newton's third law...
.
Electric propulsion thrusters for spacecraft are usually grouped in three families based on the type of force used to accelerate the ions of the plasma:
Electrostatic
If the acceleration is caused mainly by the Coulomb Force (i.e application of a static electric fieldElectric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...
in the direction of the acceleration) the device is considered electrostatic.
- Electrostatic ion thrusterElectrostatic ion thrusterAn electrostatic ion thruster is a design for ion thrusters . These designs use high voltage electrodes in order to accelerate ions with electrostatic forces.-History:...
- Hall effect thrusterHall effect thrusterIn spacecraft propulsion, a Hall thruster is a type of ion thruster in which the propellant is accelerated by an electric field. Hall thrusters trap electrons in a magnetic field and then use the electrons to ionize propellant, efficiently accelerate the ions to produce thrust, and neutralize the...
- Field Emission Electric PropulsionField Emission Electric PropulsionField-emission electric propulsion is an advanced electrostatic propulsion concept, a form of ion thruster, that uses liquid metal as a propellant. A FEEP device consists of an emitter and an accelerator electrode...
- Colloid thrusterColloid thruster]A colloid thruster is a type of thruster which uses electrostatic acceleration of charged liquid droplets for propulsion. It is closely related to electrospray ionization and other hydrodynamic spraying processes. In a colloid thruster charged liquid droplets are produced by an electrospray...
Electrothermal
The electrothermal category groups the devices where electromagnetic fields are used to generate a plasmaPlasma (physics)
In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...
to increase the heat
Heat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...
of the bulk propellant. The thermal energy imparted to the propellant gas is then converted into kinetic energy by a nozzle
Nozzle
A nozzle is a device designed to control the direction or characteristics of a fluid flow as it exits an enclosed chamber or pipe via an orifice....
of either solid material or magnetic fields. Low molecular weight gases (e.g. hydrogen, helium, ammonia) are preferred propellants 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 thruster
Cold gas thruster
A cold gas thruster is a rocket engine/thruster that uses a gas as the reaction mass.A cold gas thruster usually simply consists of a pressurized tank containing gas, a valve to control its release and a nozzle, and plumbing connecting them...
s, monopropellant rocket
Monopropellant rocket
A monopropellant rocket is a rocket that uses a single chemical as its propellant.-Chemical-reaction monopropellant rockets:...
s, and even most bipropellant rockets. In the USSR, electrothermal engines were used since 1971; the Soviet
Soviet Union
The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....
"Meteor-3
Meteor (satellite)
The Meteor craft are weather observation satellites launched by the USSR. The Meteor satellites were designed to monitor atmospheric and sea-surface temperatures, humidity, radiation, sea ice conditions, snow-cover, and clouds.-Meteor 2-21:...
", "Meteor-Priroda", "Resurs-O" satellite series and the Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
n "Elektro" satellite are equipped with them. Electrothermal systems by Aerojet
Aerojet
Aerojet is an American rocket and missile propulsion manufacturer based primarily in Rancho Cordova, California with divisions in Redmond, Washington, Orange, Gainesville and Camden, Arkansas. Aerojet is owned by GenCorp. They are the only US propulsion company that provides both solid rocket...
(MR-510) are currently used on Lockheed-Martin A2100 satellites using hydrazine
Hydrazine
Hydrazine is an inorganic compound with the formula N2H4. It is a colourless flammable liquid with an ammonia-like odor. Hydrazine is highly toxic and dangerously unstable unless handled in solution. Approximately 260,000 tons are manufactured annually...
as a propellant.
- DC arcjetArcjet rocketArcjets are a form of electric propulsion for spacecraft, whereby an electrical discharge is created in a flow of propellant . This imparts additional energy to the propellant, so that one can extract more work out of each kilogram of propellant, at theexpense of increased power consumption and ...
- microwave arcjetArcjet rocketArcjets are a form of electric propulsion for spacecraft, whereby an electrical discharge is created in a flow of propellant . This imparts additional energy to the propellant, so that one can extract more work out of each kilogram of propellant, at theexpense of increased power consumption and ...
- Pulsed plasma thrusterPulsed plasma thrusterPulsed plasma thrusters are a method of spacecraft propulsion also known as Plasma Jet Engines in general. They use an arc of electric current adjacent to a solid propellant, to produce a quick and repeatable burst of impulse...
Electromagnetic
If ions are accelerated either by the Lorentz ForceLorentz force
In physics, the Lorentz force is the force on a point charge due to electromagnetic fields. It is given by the following equation in terms of the electric and magnetic fields:...
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 thrusterElectrodeless plasma thrusterThe electrodeless plasma thruster is a spacecraft propulsion engine. It was created by Mr. Gregory Emsellem based on technology developed by French Atomic Energy Commission scientist Dr Richard Geller and Dr...
- MPD thruster
- Pulsed inductive thrusterPulsed inductive thrusterPulsed inductive thrusters are a form of ion thruster, used in spacecraft propulsion. A PIT uses perpendicular electric and magnetic fields to accelerate a propellant. A nozzle releases a puff of gas which spreads across a flat induction coil of wire about 1 meter across...
- Helicon Double Layer ThrusterHelicon Double Layer ThrusterThe Helicon Double Layer Thruster is a prototype spacecraft propulsion engine. It was created by Australian scientist Dr. Christine Charles, based on a technology invented by Professor Rod Boswell, both of the Australian National University....
- VASIMRVariable specific impulse magnetoplasma rocketThe Variable Specific Impulse Magnetoplasma Rocket is an electro-magnetic thruster for spacecraft propulsion. It uses radio waves to ionize and heat a propellant and magnetic fields to accelerate the resulting plasma to generate thrust...
Electrodynamic tether
Electrodynamic tethers are long conducting wires, such as one deployed from a tether satellite, which can operate on electromagnetic principles as generatorsElectrical generator
In electricity generation, an electric generator is a device that converts mechanical energy to electrical energy. A generator forces electric charge to flow through an external electrical circuit. It is analogous to a water pump, which causes water to flow...
, by converting their kinetic energy
Kinetic energy
The kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...
to electrical energy, or as motors
Electric motor
An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...
, converting electrical energy to kinetic energy. Electric potential is generated across a conductive tether by its motion through the Earth's magnetic field. The choice of the metal conductor
Electrical conductor
In physics and electrical engineering, a conductor is a material which contains movable electric charges. In metallic conductors such as copper or aluminum, the movable charged particles are electrons...
to be used in an electrodynamic tether is determined by a variety of factors. Primary factors usually include high electrical conductivity, and low density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
. Secondary factors, depending on the application, include cost, strength, and melting point.
Steady vs. unsteady
Electric propulsion systems can also be characterized as either steady (continuous firing for a prescribed duration) or unsteady (pulsed firings accumulating to a desired impulse). However, these classifications are not unique to electric propulsion systems and can be applied to all types of propulsion engines.External links
- NASA Jet Propulsion Laboratory
- http://alfven.princeton.edu/
- Distributed Power Architecture for Electric Propulsion
- Colorado State University Electric Propulsion and Plasma Engineering (CEPPE) Laboratory
- http://www.daviddarling.info/encyclopedia/E/electricprop.html
- http://www.nasa.gov/offices/oce/llis/0736.html