Hall Thruster Performance and Efficiency Analysis of a Molecular Propellant

An efficiency model is developed for Hall effect thrusters (HETs) operating on molecular propellants to inform which energy sinks lead to the largest degradations in HET efficiency. Similar to existing atomic efficiency models, the molecular model decomposes thrust efficiency into energy, propellant, and beam efficiencies and allows for the direct comparison of efficiencies between molecular and atomic propellants and between ionic species produced from a molecular propellant. The model was applied to experimental data on a 5 kW HET operating on nitrogen, argon, and xenon with a mass flow rate range of 5.0–5.4 mg/s and a discharge voltage range of 230–300 V. The measured thrust, specific impulse, and anode thrust efficiency ranges on each propellant are 72.8–86.8 mN, 1485–1770 s, and 32.9–39.6% (xenon); 90.2–111.9 mN, 1838–2280 s, and 25.2–29.0% (argon); and 61.4–90.0 mN, 1251–1724 s, and 12.8–16.9% (nitrogen), respectively. The low nitrogen efficiency is primarily attributed to poor mass utilization of atomic nitrogen ([Formula: see text]) and decreased energy efficiency due to molecular-specific energy sinks, such as dissociation and excitation of molecular energy modes. Despite thrust efficiencies less than 17% at current power levels, nitrogen exhibits promise operating above 5 kW due to the high voltage utilization seen with the [Formula: see text] species ([Formula: see text]).