UC Irvine

Electrospray propulsion stands out as a unique electric propulsion technology, particularly well-suited for the growing popularity of SmallSats, spacecraft with a mass below 500 kg. Microfabrication techniques are used to create highly dense arrays of emitters allowing to scale up the thrust and process the low power available in SmallSats while maintaining a very high efficiency.However, in electrospray propulsion, overspraying of the extractor and accelerator electrodes poses a significant challenge, as the accumulation of fluid on these electrodes can lead to the formation of electrically conducting films and the catastrophic shorting of power supplies. Therefore, it is crucial to have a detailed understanding of the physics of the beam and the ability to model it accurately to design electrodes effectively and predict potential impingement during the long operational periods typical of electric thrusters, which can span several years. The model presented is used to study the composition of the beam emitted by the microfabricated electrospray thruster developed by our group. The model combines two different approaches: a Lagrangian model for the inner region near the jet breakup where the trajectories of all individual charged droplets are integrated simultaneously, and where Coulomb repulsion between droplets is fully captured while integrating the equations of motion; and an Eulerian model for the outer region where the structure of the beam is obtained by computing the envelopes of beamlets in which the population of droplets is subdivided. The two regions are coupled by the initial conditions of the envelopes, which are calculated with the solution of the inner problem; and by the influence of the space charge of each region on the electric field. This strategy greatly reduces the computational time and allows to simulate the whole beam while retaining the important particle-on- particle Coulomb interaction where is significant.