Emission Modes in Electrospray Thrusters Operating with High Conductivity Ionic Liquids

Abstract

Electrospray thruster life and mission performance are strongly influenced by grid impingement, the extent of which can be correlated with emission modes that occur at steady-state extraction voltages, and thruster command transients. Most notably, we experimentally observed skewed cone-jet emission during steady-state electrospray thruster operation, which leads to the definition of an additional grid impingement mechanism that we termed “tilted emission”. Long distance microscopy was used in conjunction with high speed videography to observe the emission site of an electrospray thruster operating with an ionic liquid propellant (EMI-Im). During steady-state thruster operation, no unsteady electrohydrodynamic emission modes were observed, though the conical meniscus exhibited steady off-axis tilt of up to 15°. Cone tilt angle was independent over a wide range of flow rates but proved strongly dependent on extraction voltage. For the geometry and propellant used, the optimal extraction voltage was near 1.6 kV. A second experiment characterized transient emission behavior by observing startup and shutdown of the thruster via flow or voltage. Three of the four possible startup and shutdown procedures transition to quiescence within ∼475 μs, with no observed unsteady modes. However, during voltage-induced thruster startup, unsteady electrohydrodynamic modes were observed.

Simulation of electrospray emission processes for low to moderate conductivity liquids

“…9(a). At a lower flow rate, the jet may develop into the unstable whipping mode due to excessive electrostatic force as experimentally observed in Uchizono et al 31 Similarly, c increasing from 0:01 to 0:04 N m À1 results in increasing charge density with transition of the meniscus from concave to convex toward vacuum.…”

“…29,30 Measurements have shown the flow to be axisymmetric below the threshold when the jet begins whipping at high electric Reynolds number or low non-dimensional flow rates. 12,31 We limit the scope of our study to the steady cone-jet mode at moderate electric Reynolds number where axisymmetric modes are dominant. Sensitivity study is performed to determine the total number of mesh cells, N c , large enough to show no further dependence of the computed results on the grid size.…”

Metal Additive Manufacturing for Satellites and Rockets

“…Thrusters can be categorized based on diverse working principles, such as Hall thrusters showing a high thrust efficiency and high ion beam density due to a moderate magnetic field applied to the acceleration zone [47], pulsed plasma thrusters [48], electrospray thrusters working with ionic liquid propellants [49,50], etc. While Hall thrusters are most often used for satellites [51], applications requiring lower energies, such as the aforementioned CubeSats or other microsatellites, can be driven and navigated by microcathode arc or other plasma thrusters, field emission thrusters, electrospray thrusters, or different sorts of electric thrusters [52][53][54][55].…”

Multiscale modeling of electrospray ion emission

“…In particular, information about the dynamics of fragmentation is of particular interest to performance. 15 As in plasma devices, it is necessary to understand fundamental processes in order to design for maximum lifetime and efficiency.…”