A study on iron-composite polymer propellants for improved plasma generation in electric propulsion systems

Pulsed plasma thrusters (PPTs) are widely employed in CubeSats due to their compact size, simplicity, and ability to generate small and precise thrust. However, their low efficiency and thrust-to-power ratio limit broader adoption. This study introduces a novel PMMA-based metal-composite polymer propellant (PMMA@Fe) doped with iron powder to replace the conventional PTFE propellant. PMMA@Fe samples with iron powder concentrations ranging from 5 wt% to 20 wt% were synthesized and evaluated. The addition of iron powder reduced plasma impedance and increased discharge currents, resulting in a 62.5% improvement in impulse bit (from 80.3 μNs to 131.9 μNs) and a 63.5% enhancement in the thrust-to-power ratio (from 17.8 μN/J to 29.3 μN/J) when compared to pure PMMA. Material characterization revealed that the ablation rate of PMMA@Fe increased from 4.6 μg/shot (pure PMMA) to 8.2 μg/shot (5 wt% Fe) and plateaued at higher concentrations. Plasma plume analysis confirmed a 50 % increase in plasma generation as the iron content rose to 20 wt%, supported by a 40 % increase in optical emission intensity of PMMA decomposition species. Despite the enhanced performance, high iron content (≥15 wt%) led to irregular discharges and carbon–metal deposition, limiting the thruster's operational lifespan to 6,000 discharges. The study concludes that the PMMA@Fe propellant with 15 wt% iron offers an optimal balance, achieving 18.7 % thrust efficiency and a specific impulse of 1,324 s, while maintaining structural integrity. These findings demonstrate the potential of PMMA@Fe to enhance PPT performance for CubeSat applications.