Electric propulsion can generally be defined as propulsion that uses electricity rather than conventional chemical energy to accelerate ejection mass. Such a propulsion was first theorized by Konstantin Tsiolovsky in 1911, and thought in his time to be complete fiction and impossible to realize. However in 1964 the first ion engine was tested in space for 31 minutes, and nowadays hundreds of craft use a variation of electric propulsion.
The reason to use electric propulsion is because it is extremely mass efficient, using a very low amount propulsion mass. It is also more propulsion efficient, meaning that a higher percentage of fuel is converted to actual thrust. However, the contemporary electric thruster solutions are extremely low thrust, and thus they cannot be used for significant maneuvers, such as leaving the Earth's gravity well. The technology to create an electric thruster is also more complex than chemical thrust.
There are four main categories of electric propulsors:
- Electrostatic
- Uses ionisation and electric fields to accelerate ejection mass
- Electrothermal
- Uses electricity to generate heat that creates pressure which accelerates ejection mass
- Electromagnetic
- Moves ejection mass through a magnetic field to accelerate it
- Alternative methods
- E-sails
- Nuclear electric
Each of these categories have multiple thruster technologies in them. Electrostatic propulsion currently includes electrospray, Hall effect, and gridded iron technologies. These technologies stay under 100 mN of thrust in miniaturized versions, and range in size from 2.5 cubic cm to 50 cubic cm. For ejection mass, ionisable or ionised material is suitable. Electrothermal includes arcjet and resistojet technologies. Arcjet technology can generate ~300mN of thrust for ~2kW, while resistojets generate ~1mN per ~5W. For these propulsors performance is very dependent on the fuels such as hydrazine, H2O, Ar, or H2, and they are generally less fuel efficient than other technologies. Electromagnetic technologies include pulsed plasma and magnetoplasmadynamic propulsors, that are difficult to develop, high cost, and can use up to hundreds of kW. However, in theoretical models MPD is the most powerful of all electric propulsion technologies, and can use solid fuel, not only gaseous or fluid.
Paper: https://www.mdpi.com/2226-4310/8/1/22/htm
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