Accurate Measurement of Nano-Newton Thrust for Micropropulsion System Characterization

The ability to measure extremely low thrust levels with unusual precision is becoming more critical as attempts are made to characterize the performance of emerging micropropulsion systems. Many new attitude control concepts for nanospacecraft involve the production of thrust below 1 μN. A simple, but uniquely successful thrust stand has been developed and used to measure thrust levels as low as 88.8 nano-Newtons with an estimated accuracy of ±16%. Thrust levels in the range of 734 nano-Newtons to 1 μN have been measured with an estimated accuracy ±2%. Thrust is measured from an underexpanded orifice operating in the free molecule flow regime with helium, argon, and nitrogen propellants. The thrust stand is calibrated using results from Direct Simulation Monte Carlo numerical models and analytical solutions for free molecule flow. The thrust stand exhibits a significant improvement in accurate, low thrust measurements compared to published results.