Trends in Performance Improvements of a Coaxial Gas-Fed Pulsed Plasma Thruster∗

The performance of a coaxial gas-fed pulsed plasma thruster is shown to improve with increasing capac-itance. We report experimental results which show that raising the capacitance from 94 µF to 180 µF at a pulse energy of 5 J has uniformly increased the thrust efficiency over all specific impulses by a factor of 1.2. Thrust efficiencies as high as 69 % were at-tained. This increase, however, is below the predicted trend from a simple analytical impulse model. To un-derstand this discrepancy and explore other trends, a more detailed one-dimensional numerical model was developed. This model uses an RLC circuit potential equation for the discharge electrical characteristics and a snow-plow model for mass accumulation. From this analysis it is clear that the dynamic efficiency of the gas sweeping process plays an important role in determining the effect of increasing capacitance on performance. By comparing the trends predicted by the one-dimensional numerical model with the mea-sured data it was possible to infer that the limited performance improvement may be blamed on the in-creased capacitance causing the discharge to reach the edge of the electrodes before the capacitor is fully discharged