Scaling Laws for Pulsed Electric Propulsion with Application to the Pluto Mission

A set of universal laws for the scaling of pulsed elec-tric propulsion systems is presented. The Langmuir characteristic velocity and another characteristic ve-locity defined here as the pulsed electric propulsion (PEP) characteristic velocity are the two governing parameters in these scaling laws. The Langmuir and PEP characteristic velocities describe the relation of the power generator mass and the energy storage sys-tem mass to the propellant mass required to perform a given mission. An optimal exhaust velocity that maximizes the useful mass fraction of the spacecraft can be found using these two parameters. This tech-nique especially applies to low power, small space-craft where the mass of the energy storage system could make up a significant fraction of the total mass. An Ablative Pulsed Plasma Thruster (APPT) is used as an example low power pulsed electric propulsion system applied to the Pluto Express Mission. A 100% increase in the scientific payload mass of a recent probe design is demonstrated by replacing the chem-ical propulsion system with an optimized APPT sys-tem using only well proven off-the-shelf technologies.