Rocket Propulsion/Electric Propulsion

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Contents 1 Introduction 2 Forms of Electric Propulsion 2.1 Electrothermal 2.1.1 Resistojets 2.1.2 Arcjets 2.2 Electrostatic 2.2.1 Ion Engines 2.2.2 Hall Thrusters 2.3 Electromagnetic 2.3.1 Magnetoplasmadynamics (MPD) Thrusters 2.3.2 Pulsed Plasma Thrusters (PPTs) 2.3.3 Colloid Thrusters 2.3.4 Field Emission Electric Propulsion (FEEP) 2.3.5 Vacuum arc thrusters (VATs)

[edit] Introduction

Electric Ion rockets use xenon atoms charged with [w:|radio waves] to create thrust. When thinking about rockets already in space, it is easy to forget that moving them around is not all about playing with fire. Although electric ion thruster technology is currently unable to launch a space craft directly off the Earth's surface, it can produce a small amount of thrust that would help it navigate in space.

To understand how this works you have to think of how charged objects are attracted to or repulsed by other charged objects. Electrically charged gases are called ionization ions. Xenon is a [w:Noble_gas|noble gas] with a complete electronic outer shell. Its outer shell can be ionized with radio waves stripping outer layer electrons and leaving behind a positively charged ion. The ion can then be moved by introducing an electric field. This is typically done with two oppositely charged metal plates, at least one of which is perforated to allow the accelerated ions to pass through and exit the nozzle of the rocket. This does not create much thrust, but it is very efficient and can produce incredibly high speeds over great distances.

[edit] Forms of Electric Propulsion

[edit] Electrothermal

Electrothermal propulsion produces thrust by electrically heating propellant to very high temperatures and expanding it through a nozzle. This process is similar to the process used by chemical rocket propulsion, except the propellant is heated electrically instead of by combustion.

[edit] Resistojets

Resistojets heat propellant electrically through the use of an electric heater. Their first use was in 1965 on board U.S. Department of Defense satellites. These particular resistojets used nitrogen as propellant.

[edit] Arcjets

Arcjets are very similar to resistojets, except arcjets heat propellant electrically through the use of an electric arc. This electric arc heats propellant to temperatures greater than 3000°C.

[edit] Electrostatic

[edit] Ion Engines

[edit] Hall Thrusters

[edit] Electromagnetic

[edit] Magnetoplasmadynamics (MPD) Thrusters

[edit] Pulsed Plasma Thrusters (PPTs)

Pulsed Plasma Thrusters operate by ablating Teflon material between two electrodes by means of an electric arc. The Lorentz force accelerates the material out as thrust.

[edit] Colloid Thrusters

[edit] Field Emission Electric Propulsion (FEEP)

[edit] Vacuum arc thrusters (VATs)

VATs operate by vapourising and ionising cathode material by means of a vacuum arc. The plasma accelerates outward as thrust.