A pulsed electric thruster for satellite control

Abstract

The research performed on a solid Teflon pulsed plasma thruster (PPT), four of which are currently providing east-west stationkeeping for the Lincoln Laboratory LES-6 communications satellite, is presented. A detailed description of the thruster operation supported by diagnostic measurements is given. First a circuit model was developed for the thruster which accurately predicted impulse bit (∼ 31 µNċs), specific impulse (∼ 300s), and gave an energy balance. It showed that ∼30 percent of the energy is lost in capacitor dissipation. Most of the remainder is lost to ionization and heating. Image converter pictures of the discharge showed a traveling plasma and a standing arc. A number of plasma diagnostics were set up, including a He-Ne Mach-Zehnder interferometer and a K-band microwave interferometer. These measured electron densities in the arc discharge and downstream. A spectrographic analysis of the plasma showed that neutral, singly, doubly, and triply ionized atoms of carbon and fluorine were present and that the greater the degree of ionization the higher the specie's velocity. A Faraday cup examination of the exhaust plume showed the beamwidth of the ∼36° and ionization no greater than 10 percent. Velocity and ionization data imply that the ions could conceivably account for all of the thruster's performance.