General Description
Ion thrusters use beams of ions (electrically charged atoms or molecules) to create thrust in accordance with momentum conservation. The method of accelerating the ions varies, but all designs take advantage of the charge/mass ratio of the ions. This ratio means that relatively small potential differences can create very high exhaust velocities. This reduces the amount of reaction mass or fuel required, but increases the amount of specific power required compared to chemical rockets. Ion thrusters are therefore able to achieve extremely high specific impulses. The drawback of the low thrust is low spacecraft acceleration, because the mass of current electric power units is directly correlated with the amount of power given. This low thrust makes ion thrusters unsuited for launching spacecraft into orbit, but they are ideal for in-space propulsion applications.
Various ion thrusters have been designed and they all generally fit under two categories. The thrusters are categorized as either electrostatic or electromagnetic. The main difference is how the ions are accelerated.
- Electrostatic ion thrusters use the Coulomb force and are categorized as accelerating the ions in the direction of the electric field.
- Electromagnetic ion thrusters use the Lorentz force to accelerate the ions.
Power supplies for ion thrusters are usually solar panels, but at sufficiently large distances from the Sun, nuclear power is used. In each case the power supply mass is essentially proportional to the peak power that can be supplied, and they both essentially give, for this application, no limit to the energy.
Electric thrusters tend to produce low thrust, which results in low acceleration. Using 1 g is 9.81 m/s²; F = m a or a = F/m
An NSTAR thruster producing a thrust (=force) of 92 mN will accelerate a satellite with a mass of 1000 kg by 0.092 / 1000 = 0.000092 m/s² (or 9.38E-6 g).
Read more about this topic: Ion Thruster
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