PLASMA ENGINE

A plasma engine is an electric propulsion drive system that uses plasma, a high energy state of matter to generate thrust. Plasma is a state of matter; the other three commonly known states are solid, liquid and gas. Plasma is characterized by the presence of a significant portion of charged particles such as ions and electrons. Plasma can be generated by heating a neutral gas or subjecting it to a strong magnetic field so that some of the electrons are freed from the atoms or molecules. It then changes its state and becomes a mixture of partially ionized gas, containing ions, electrons and neutral atoms.

There are several types of plasma engines which includes; ion engines, Hall Effect thrusters (HETs), magneto-plasma dynamic thrusters (PPTs), and electrostatic ion engines.

The main component of a plasma engine are as follows; power processing unit (PPU), ionization chamber, accelerator, neutralizer, propellant management system (PMS), thermal management system (TMS) and the control system.

The power processing unit (PPU) is responsible for converting the electrical energy from the power source into a high voltage, high current output that is used to power the plasma engine.

The ionization chamber is where the propellant typically xenon gas is ionized into a plasma state.

The accelerator is responsible for accelerating the ions to high speed, typically using an electrostatic or electromagnetic field.

The neutralizer is responsible for neutralizing the ions that are accelerated by the accelerator typically by injecting electrons into the plasma.

The propellant management system (PMS) is responsible for managing the flow of propellant to the ionization chamber.

The thermal management system (TMU) is responsible for managing the temperature of the plasma engine typically by using radiators or heat pipes.

The control system is responsible for controlling the operation of the plasma engine by using sensors and actuators.

A plasma engine power source is usually from an array of solar panels or a nuclear reactor and it is used to generate electrical energy.

The propellant is usually xenon gas which is stored in tanks within the spacecraft.

The ionization chamber is where the xenon gas is ionized to create plasma.

The electrostatic grids are used to accelerate the ions and create thrust.

The neutralizer is used to neutralize the ions thereby creating a neutral beam of particles.

In their operation the xenon gas is ionized in the ionization chamber creating a plasma of positively charged ions and negatively charged electrons.

Then the ions are accelerated through the electrostatic grids which are biased at high voltages. This creates an electric field that accelerate the ions. As the ions are accelerated they are expelled out of the back of the space craft creating a reaction force that propels the space craft forward.

The ions are neutralized by the neutralizer which adds electrons to the beam, creating a neutral beam of particles. The neutral beam of particles is expelled out of the back of the space craft creating a high speed exhaust that generates thrust.

The advantages of a plasma engine are; plasma engines are highly efficient with specific impulse values ranging from 3000 to 5000 seconds. Plasma engines can operate for thousand of hours. Plasma engines are comparatively lighter than conventional chemical propulsion systems.

The disadvantages are; plasma engines produces low thrust, require a high amount of electric power and are very complex requiring sophisticated control power systems to operate.

Plasma engines find application particularly in space exploration, satellite propulsion and interplanetary mission.

The future of plasma engines depends on the developments in the following technologies;  new materials, new designs of engine and the use of advanced propellant such as water or air rather than the traditional or conventional xenon gas would enable higher power levels, efficiency and as well as low cost of both deployment, operation and maintenance of plasma engines.

SOURCES:

• Electric propulsion for spacecraft by Juan R. San-martin.
• Spacecraft propulsion by Charles D. Brown.
• Electric propulsion system by Richard G. Jahn and Eric Y. Choueri.
• Plasma propulsion systems by Martin A. Lieberman and Allan J. Lichtenberg.
• Ion engines for space propulsion by Ernst Eckhard and Holger Kersten.