AFRL MicroPPT Development for Small Spacecraft Propulsion

A class of miniaturized pulsed plasma thrusters (PPT), known asMicroPPTs, ' is currently in development at the Air Force Research Laboratory. The MicroPPTs use a surface discharge across solid propellant to provide precise impulse bits in the 10 range. In the near term, these thrusters can provide propulsive attitude control on spacecraft using the dry mass of conventional torque rods and reaction wheels. ' Eventually these thrusters are designed for primary and attitude control propulsion on 25-kg class spacecraft. Efforts to characterize MicroPPT performance and the thruster plume are underway. To this end, a modified torsional thrust stand has been developed for the purpose of accurately measuring the low-level thrust generated by the MicroPPT. A Hemott Cell interferometer is introduced to establish the electron and neutral densities in the thruster plume. Comparison of the measured electron density with modeling predictions shows close agreement. Additionally, a Pockels cell has been developed to provide a zero-impedance MicroPPT breakdown voltage measurement, and an intensified CCD array has been used to characterize the divergence of both the thruster plume and the particulate emission. A synopsis is also presented of the status of the thruster development, including lifetime, thermal, and environmental testing