CONICET | Buscador de Institutos y Recursos Humanos

Small satellites of a few kilogram mass offer the great advantage of affordable construction and deployment costs. Due to their relative simplicity and compactness, ablative pulsed plasma thrusters (APPT) are a good option as a means of propulsion for these satellites, either for attitude control or orbit maintenance. In APPT a pulsed electrical discharge generates a plasma from a small quantity of mass ablated from the dielectric insulating the electrodes, usually Teflon. The same electrical current of the discharge accelerates the plasma by Lorentz forces and/or pressure gradients due to joule heating, resulting in impulse bits of a few tens of microNewton-sec per input Joule. The large number of different processes involved makes the APPT numerical modeling and optimization a difficult task. We present in this work a self-consistent numerical model capable of accounting for the main processes: Teflon ablation, plasma generation and further evolution, coupled to the circuit driving the discharge. The model assumes a one fluid, quasi-neutral Teflon plasma in local thermodynamic equilibrium, with ionization degree determined by Saha?s equation. Modeled radiative and convective energy fluxes to the walls determine consistently the wall temperature and the ablation of Teflon. The non-stationary equations for mass, momentum and energy of the Teflon plasma are solved in a one-dimensional plane or cylindrical duct of variable cross section, using a TVD MacCormack numerical scheme. The electrodes potential and electrical current density in the plasma are coupled to the electrical circuit driving the discharge, modeled as a series resistor-inductor- capacitor. Plasma resistance and inductance are included in the circuit equation, which is solved simultaneously with the plasma evolution equations. Runs of the model are compared with the experimentally determined mass ablation and time evolution of the discharge made in our group for a cylindrical APPT