Facility pressure effects on thrust measurement of micronozzles and thrust correction for space applications

Abstract

Accurate thrust estimation of low-Reynolds-number micronozzles is essential for designing reliable micropropulsion systems. However, ground-based measurements are influenced by facility pressure effects, which reduce the measured thrust due to rarefied gas interactions between the nozzle jet plume and the ambient gas. This study aims to identify the key parameters of and develop a thrust correction model for the facility pressure effect, grounded in a gas depletion framework. Direct simulation Monte Carlo simulation reveals that thrust decreases as the inverse nozzle pressure ratio increases, with this reduction varying significantly based on the throat Reynolds number. In terms of nozzle geometry, the divergence angle and expansion ratio had minimal effects, while the exit wall radius had a substantial impact on thrust reduction. Although gas species influenced specific impulse efficiency, the thrust reduction caused by the facility pressure remained nearly independent of gas species. Based on the simulation results, the correction factor in the gas depletion model was empirically formulated. The model accurately predicted thrust reductions of up to 50 %, with a maximum estimation error of 2.2 %. This approach allows for precise prediction of in-space nozzle performance from ground test data, supporting the operational reliability of small spacecraft.