Approach to the parametric design of ion thrusters

A methodology that can be used to evaluate ion thruster performance capabilities is presented. It can be applied to determine which of several physical constraints limit ion thruster power and thrust under various design and operating conditons. Results are presented for a typical case in which power and thrust are limited by grid system span-to-gap, intragrid electric field, discharge chamber power per unit beam area, and screen and accelerator grid lifetime constraints. In this case the thruster operating condition is selected to assure maximum thrust-to-power over a range of beam areas and specific impluses. It is pointed out that other operational objectives such as optimization of payload fraction or thrust duration for a mission of interest can be substituted readily for the thrust-to-power objective. An important result illustrated by an example case is that the specific impulse at which a typical ion thruster operates can be increased substantially above the value that produces maximum payload fraction without inducing a substantial loss in the payload fraction.