A multi-scale approach to electrospray ion source modeling has been developed. The evolution of a single-emitter electrospray plume in a pure ionic regime is simulated with a combination of electrohydrodynamic fluids and n-body particle modeling. Simulations are performed for the ionic liquid, EMI-BF4, firing in a positive pure-ion mode. The metastable nature of ion clusters is captured using an ion fragmentation model informed by molecular dynamics simulations and experimental data. Results are generated for three operating points (120, 324, and 440 nA) and are used to predict performance relevant properties, such as the divergence angle and the extractor surface impingement rate. Comparisons to experimental data recorded at similar operating points are provided.

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In order to better evaluate the trade-offs between different simulation options for an electrospray thruster plume, we have developed a multi-scale n-body code to compute the evolution of a single emitter electrospray plume in the pure ionic regime. The electrostatic force computations in the simulation are captured through the use of three different computational algorithms with various degrees of approximation. The results of the simulations for a simple test case are compared in terms of computational speed and accuracy. The test case utilizes a single operating point (323nA) for a stable meniscus solution for the ionic liquid EMI-BF4 firing in the positive pure ion mode. Complex species and probabilistic fragmentation processes are neglected. An overview is provided of the trade-off between accuracy and computational speed for the three algorithms in the context of simulating the electrostatic interactions between particles. For a large number of particles, the faster algorithms show a significant reduction in computational time while maintaining a high level of accuracy with a proper choice of tuning parameters.

This paper presents an initial feasibility study on the use of ionic-liquid ion sources for electrostatic actuation on atmosphere-less planetary bodies. The natural surface charging of atmosphere-less planetary bodies has been studied as the cause of the transport of regolith across the surface and for electrostatic levitation of a spacecraft in proximity to small asteroids. The low magnitude of the natural surface electric field (order 10 V/m) severely limits the capability of a vehicle to leverage electrostatic levitation as its maneuvering strategy, particularly on large planetary bodies such as the Moon. Ionic-liquid ion sources are considered as an actuator for charging of both the vehicle as well as the local surface of the planetary body. By irradiating the surface with ions, the surface electric field can be increased far beyond its natural value and could enable electrostatic levitation on planetary bodies as large as the Moon with current technology. A low-fidelity analytical model of the charging process is developed in order to estimate requirements on the local surface charge density and limitations on the vehicle's levitation height and translational speed. Experiments are conducted in a laboratory environment to demonstrate the feasibility of using ionic-liquid ion sources for combined vehicle and surface charging by creating a 1 mN electrostatic force through charge transport while requiring only 0.2 mW of input power. These experiments are in reasonable agreement with the low-fidelity model that describes the fundamental physics of this concept.