Experimental and Numerical Determination of Micropropulsion Device Efficiencies at Low Reynolds Numbers

TLDR

Low‑thrust propulsion for micro‑ and nano‑spacecraft requires efficient nozzle expansions, a growing need driven by the low Reynolds number flows that characterize such systems. The authors investigated helium and nitrogen flows through a small conical nozzle and thin‑walled orifice using Direct Simulation Monte Carlo and a nano‑Newton thrust stand, then validated the model with experimental data and employed it to study the effects of geometric variations. For throat Reynolds numbers below 100 the nozzle‑to‑orifice thrust ratio is below unity, yet specific impulse remains above one across 0.02–200, and geometric adjustments can increase specific impulse by 4–8 % at low Reynolds numbers.

Abstract

Abstract : The need for low thrust propulsion systems for maneuvers on micro- and nano-spacecraft is growing. Low thrust characteristics generally lead to low Reynolds number flows from propulsive devices that utilize nozzle expansions. Low Reynolds number flows of helium and nitrogen through a small conical nozzle and a thin-walled orifice have been investigated both numerically, using the Direct Simulation Monte Carlo technique, and experimentally, using a nano-Newton thrust stand. For throat Reynolds number less than 100, the nozzle to orifice thrust ratio is less than unity; however, the corresponding ratio of specific impulse remains greater than one for the Reynolds number range from 0.02 to 200. Once the Direct Simulation Monte Carlo model results were verified using experimental thrust and mass flow data, the model was used to investigate the effects of geometrical variations on the conical nozzle's performance. At low Reynolds numbers, improvements to the specific impulse on the order of 4 to 8% were achieved through a combination of decreasing the nozzle length and increasing the nozzle expansion angle relative to the nominal experimental geometry.