Measurement of the Fragmentation Rates of Solvated Ions in Ion Electrospray Thrusters

Formation and fragmentation of 2-hydroxyethylhydrazinium nitrate (HEHN) cluster ions: a combined electrospray ionization mass spectrometry, molecular dynamics and reaction potential surface study

“…The principle and techniques of the electrospray thruster have been discussed in many works. 14,16,17,33,[35][36][37][38][39][40][41][42][43][44][45][46][47] In brief, a high electric field is applied to ILs at a spray emitter leading to the formation of a Taylor cone at the emitter tip 12,48 and the emission of charged IL droplets and ions from the Taylor cone into the gas phase. As the emitted charged species are accelerated in a high electric field to produce a thrust, the spacecraft is accelerated in the opposite direction to the ions.…”

“…The droplet mode produces a large thrust (F) that is proportional to ffiffiffiffiffiffiffiffi ffi m=z p . The second extreme is a purely ionic mode where the emission is dominated by small ions with large ratios of z/ m. 17,36,40 In the purely ionic mode, every ion is efficiently used, resulting in a high specific impulse (I sp , the change in momentum per unit mass for rocket fuels, a key metric in assessing propulsion efficiency) that is proportional to ffiffiffiffiffiffiffiffi ffi z=m p . 14 In the electrospray thruster, greater than 90% propellant utilization is desired for mission planning, 35 yet many factors result in deviations from the theoretical optimum.…”

“…As the outcome of kinetics-controlled in-source cluster formation and inand after-source cluster fragmentation may not be accurately predicted on the sole basis of thermodynamics, molecular dynamics simulations are needed to elucidate mechanisms of these events. 53,54 For the electrospray thrusters operating in the purely ionic regime, formation of undesirable IL cluster ions, 17,33,40,41,43 in addition to single ions, brings about several specific issues: (1) I sp of the propellant is decreased by large cluster ions; (2) cluster ions of the same charge but different masses are accelerated to different final velocities and momenta by the same electric field, and the resulting ionbeam polydispersity limits the propulsion efficiency; 35,39 (3) cluster ions are metastable (lifetime of ms) 40 and undergo inflight dissociation. 56 Cluster fragmentation may occur via various mechanisms in a spacecraft, e.g., the emitted species strike a downstream surface (i.e., liberation of materials in sputtering), 46,47 the backscattering clusters (happening in a bipolar electrospray thruster) impact the surface of the spacecraft, 16 and collisions between the emitted species in ''traffic jams'' within the electrospray plume (because of the differences in their velocities).…”

Influence of Magnetic Nanoparticles and Magnetic Stress on an Ionic Liquid Electrospray Source

“…In a study on the beam energy of an externally wetted EMIM-BF4 electrospray source, Miller and Lozano concluded that similar poly-energetic RPA traces were the result of fragmentation of dimer ion species into monomer species within the extraction field. [44] Thus the lower-energy, secondary populations presented in Figure 5.10. could be the consequence of ion species fragmenting from droplets or off NPs partway through the extraction field of the source.…”

“…Therefore, producing a highly-collimated spray at the maximum possible energy provided by the extraction field is desired. Literature exists on the measurement of beam energy and divergence for multiple electrospray sources and propellants [43,44,89,95]…”