Analysis of an Electrospray Thruster with a Concave Propellant Meniscus

The low thrust, high specific impulse, and low mass of electrospray thrusters (ETs) make them ideal for maneuvering nanosatellites, especially with the new requirement to deorbit a satellite within five years of completing its mission. These innovative thrusters use electrohydrodynamic principles of electrospray (ES) to provide thrust. These principles have been subject to much research over the past decade, though much more research is needed to fully understand the underlying physics of these thrusters. The first part of this study establishes a procedure for analyzing the theoretical thrust performance of an ET, by using propellant properties and well-documented ES scaling laws to identify the ES mode and governing equations applicable to the ET of interest. Next, this procedure is demonstrated by analyzing a novel ET in development at the University of Tennessee Space Institute, which culminates in the comparison of three theoretical thrust density and specific impulse equations based on geometry, electric pressure, and Ohmic conduction. The second part of this study will focus on a numerical analysis of ES produced from a concave meniscus using ANSYS Fluent. The novel ET will use capillary action to drive propellant through its capillaries, unlike most ETs that use a pump. The capillary action will result in the propellant forming a concave meniscus at the end of the capillary. There is little research on whether a concave meniscus can produce ES because most studies assume the meniscus is initially flat or in the Taylor cone shape. This model will focus on ES on the microscale using a low-conductivity fluid flowing through a charged capillary. The numerical model used in this study is verified by comparing the jet diameter produced by the model with well-established microscale ES scaling laws for the jet diameter. The results of this numerical model show that it is possible to produce a Taylor cone and an unsteady jet from a concave meniscus. Finally, this study will make recommendations on future work for analyzing and understanding the underlying physics of ETs.