Plasma plume characterization of electric solid propellant pulsed microthrusters

Electric Solid Propellants are an exciting potential option for propulsion because they are ignited only by an applied electric current. This leads to exciting capabilities such as on-demand throttling and re-ignition, and insensitivity to accidental ignition by spark, impact or open flame. Digital Solid State Propulsion has developed a pulsed microthruster using an electric solid propellant. In this work, the plasma plume created by these microthrusters is investigated using a nude Faraday Probe, an array of single Langmuir Probes, a triple Langmuir probe and Residual Gas Analysis. The thruster was tested at a vacuum level of 2×10^-5 Torr. Results indicate a peak centerline ion current density of about 200 mA/cm², peak electron temperature of about 1 eV and peak electron density of between 1 and 2×10¹¹ cm^-3. Additionally, ionization fraction estimates are < 1% of an ablation mass bit of about 250 µg on average. Exhaust velocity estimates are largely inconclusive, but are on the order of a few km/s.