Investigative Report Effect of Gas Molar Mass on the Thrust Performance of DIY Ion Thrusters

This investigative laboratory report explores how the molar mass of different propellant gases affects the thrust performance of small-scale, DIY ion thrusters. Conducted as pre-university experimental research, the study applies key principles from plasma physics, gas dynamics, and aerospace propulsion engineering to quantify the performance trade-offs of various gases in electric propulsion systems.The report covers:Ion thruster design and build – Construction of a simple grid-type ion thruster using accessible materials.Propellant selection – Comparative testing of gases with varying molar masses.Thrust measurement – Use of a sensitive balance to record micro-thrust output in controlled conditions.Performance correlation – Analysis of molar mass against thrust, ionisation efficiency, and exhaust velocity.Theoretical grounding – Application of the ideal rocket equation and electric propulsion fundamentals.Experimental limitations – Discussion of measurement sensitivity, grid spacing, and ionisation energy constraints.The findings confirm that propellant molar mass plays a measurable role in ion thruster performance, with lighter gases generally enabling higher exhaust velocities, while heavier gases can produce greater impulse per ion but at lower velocities.