Estimation of the sublimation of the propellant after the pulse discharge in a parallel-plate pulsed plasma thruster

One of the electric propulsion systems suitable for microsatellites is the pulsed plasma thruster (PPT). In this study, the thrust characteristics and efficiency are evaluated when the input energy to the PPT is changed. Generally, the mass of solid propellant (Teflon) consumed is used to calculate the specific impulse. However, sublimation from the Teflon propellant surface continues even after the pulse discharge ends, and the gas generated after that is not accelerated and does not contribute to the thrust. In other words, the mass of the gas that is not accelerated is also included in the estimation of the specific impulse. The proportion of gas generated after the discharge is not yet well understood. Here, the specific impulse can also be estimated using the plasma velocity. The plasma velocity was measured using a double probe. When the plasma flows into the probe, a current corresponding to the time change of the plasma density flows, and the plasma velocity is measured from the time delay between the upstream and downstream currents. The plasma velocity was estimated to be about 35 km/s, and the propellant loss rate was about 45 %.