Potential Ionic Liquid Characterization and Testing for Ion Electrospray Thrusters

Ion electrospray propulsion is a highly effective electric propulsion technology for CubeSats and other small satellites in which ionic liquids (ILs) are used as propellants for their unique properties. There is a wide range of unexplored ILs with fascinating attributes, and making the right choice is key to maximizing the ion electrospray thrusters’ (IETs’) performance. In this work, four novel ILs were tested and characterized: 1-ethyl-3-methylimidazolium phosphate (EMI-PO₄), N-methyl-N-butylpyrrolidinium dicyanamide (MBPyrro-DCA), Triethylsulfonium bis(trifluoromethylsulfonyl)imide ( $S_{222}$ -TFSI), and 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMI-TfO). These were selected for their exceptional properties, such as high viscosity, density, and conductivity, double ion presence, absence of fluorine, symmetry/asymmetry of their ions, surface tension (ST), and ion masses. Carbon xerogel and glass fiber emitter arrays were successfully employed in this research. The tests performed for the characterization were emission current and interception, energy distribution, spatial beam distribution, and mass distribution. The results were compared with 1-ethyl-3-methylimidazolium trifluorotrifluoroborate (EMI-CF₃BF₃), which is taken as a reference for being a well-characterized IL. Aspects like firing stability, current level, fragmentation, beam angle, and $I_{\text {sp}}$ were analyzed to determine the performance of the novel propellants. As a result, their main benefits and some drawbacks were identified, highlighting the potential of EMI-PO₄.