Plasma Modeling
We study the multiscale modeling of electrospray thruster plume, from binary inter-particle collisions (nm scale) to plume interactions (mm scale) in an array and multi-array effects (cm scale). We aim to patch the models at different size scales to form a comprehensive plume model that will capture all the complex underlying physics driving the plume evolution. In parallel, we extend this multiscale framework to higher-power electric propulsion systems by modeling plasma energy deposition and power-loss pathways within the discharge, enabling physics-based thermal modeling of high-power thrusters.
Molecular dynamics simulations of propellant-propellant interactions
(PhD Student: Abu Taqui Md Tahsin)
Electrospray thrusters represent an attractive technology for micropropulsion of small satellites. They produce thrust by ejecting charged molecules at high velocities using strong electric fields. However, the molecules present in the plume are susceptible to collision, chemical reaction, and fragmentation, which may introduce different new species with various mass-to-charge ratios inside the plume. Prediction of the byproducts that appear upon collisions is of prime importance to predicting the evolution of the plume and estimating the performance and the lifetime expectancy of the thruster. We use molecular dynamics simulations on the Large-scale Atomic Molecular Massively Parallel Simulator (LAMMPS) to investigate monomer-neutral collisions at different impact configurations, impact energies, and impact parameters, and obtain the mass spectra of the resulting species.
Pure Momentum Exchange
Ionic Fragmentation
Charge Exchange
Covalent Fragmentation
Recombination
Five types of monomer-neutral collisions [Tahsin et al., AIAA SciTech 2024]
Molecular dynamics simulations of propellant-surface interactions
(Post Bac: Nicholas Laws)
Electrospray ionic liquid ion sources used for micropropulsion operate in the pure ion regime by emitting metastable, low solvation ion clusters whose unimolecular dissociation can reshape plume composition, energy distributions, and diagnostic observables. Motivated by the contrast between microsecond scale, field-free decay measured downstream and the strong, rapidly varying fields experienced during nanosecond acceleration, this work leverages ensemble-scale microcanonical molecular dynamics simulations in LAMMPS to quantify thermal and field-assisted breakup of \ce{EMI-BF4} dimers, trimers, and tetramers. Trajectories are sampled across 600 to 1000 K and uniform electric fields of 106 to 109 V/m, with lifetimes extracted via a connectivity-based fragmentation criterion and products classified to obtain pathway-resolved branching probabilities. The results reveal a universal transition from a low-field, temperature-controlled regime to a strong field regime where electrostatic work collapses lifetimes by orders of magnitudes and drives topology changes such as charged core ejection. The MD dataset is reduced to compact parameterizations of lifetime that provide transferable kinetic inputs for multiscale electrospray plume transport models.
n-body Ion Beam Simulation
(PhD Students: Adler Smith)
A gridless particle-particle simulation technique is used to model the acceleration region of a single emitter [Petro et al., JAP 2022]. This model includes the electrohydrodynamic emission (EHD) model [Gallud et al., JFM 2022] to inject particles into the computational domain. Charged particles are accelerated downstream due to a Laplace field between the emitter and the extractor. A leap-frog integrator is used to integrate the particle trajectories.
324 nA n-body simulation
Analytical Study of Electrospray Plume
(Post Doc: McKenna Breddan)
Electrospray thrusters have high potential for power-limited endeavors, such as small satellite and deep space missions. However, their complexity has prevented the development of an analytical description for plume shape, necessitating costly and time-intensive experimental and computational research. The discovery of a simple mathematical description of plume shape based on emitted particle properties and environmental variables (like pressure and electric field strength) would save substantive investment in characterizing electrospray plumes. We created a simplified version of an electrospray and determined mathematical descriptions of resulting plume shape which show dependences on particle charge and emission velocity, paving the way for future analytical studies to build system complexity back towards a physical electrospray. We use particle dynamics data from our in-house N-body electrospray code Adaptive Resolution Electrospray Simulation (ARES) to determine the best-fit functions to plume shape and perform a parameter sweep of emitted particle properties to investigate how the best-fit function coefficients depend on particle properties.
Analytical Study of Plasma Energy Deposition Models
(PhD Student: Kaylin Borders)
This work develops and compares analytical plasma energy deposition models to quantify heat generation and thermal loading in Hall effect thrusters operating with multiple propellants. By resolving how discharge power is distributed among ions, electrons, neutrals, radiation, and wall interactions, the study links plasma physics directly to thruster thermal behavior. Originally formulated for xenon, the models are extended to krypton, argon, and water vapor, incorporating propellant-specific ionization costs and excitation pathways. Applied to a representative SPT-100 operating condition and extrapolated to higher power, the results highlight how propellant choice and modeling assumptions influence wall heating and thermal response. Together, this framework provides a physically grounded foundation for thermal management and design of future high-power electric propulsion systems.
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Kinetic Ion Beam Modeling for Electrospray Thrusters
Sustainable space exploration requires longevity and flexibility in satellite platforms. For small satellites, compact electric propulsion devices such as electrospray thrusters can significantly extend lifetime and capability. As these devices operate under different principles and with more complex propellants than traditional plasma thrusters, fundamental modeling of the ion emission process and plume-spacecraft interactions are required. Towards this end, we have developed a kinetic model of the plume evolution of an electrospray ion source that tracks processes at the individual ion level. This model can be used to predict the trajectory of plume ions and neutral bi-products and their impact on performance. As a spacecraft-integrated device would have thousands of emission sites, further research will include the physics of the composite plume.
[Petro et al., IEPC 2019]
Expansion to Multi-emitter Arrays
(PhD Student: Adler Smith)
A multi-scale approach to multi-emitter electrospray ion source modeling has been developed and integrated with the Air Force Research Laboratory’s (AFRL) Thermophysics Universal Research Framework (TURF). This framework is used to extend single-emitter models of electrospray plume evolution to the array-scale using the PIC method. Source models for individual emission sites are informed by an n-body single-emitter model. Molecular effects such as ion-cluster fragmentation are included. This model is used to predict array-level properties such as plume divergence angle, and demonstrate the computational feasibility of modeling many emitters in parallel.
[Smith et al., AIAA SciTech / JPP 2023]
Designing Propulsion systems for In-Situ Resource Compatability
We have been studying the efficacy of replacing traditional noble gas propellants used in plasma propulsion devices with gaseous water. We have analyzed plasma generation efficiency which is applicable to a range of propulsion devices [1] and the efficiency of various non-contact plasma acceleration schemes [2,3]. Methods we have used include plasma-chemical analyses coupled with particle-in-cell modeling and quasi-1D plasma flow approximations. Our current research focus involves the study of dual-mode devices for flexible mission architectures using a shared propellant and efficiency improvements for water-plasma devices.
[1] Petro and Sedwick, Effects of Water Vapor Propellant on Electrodeless Thruster Performance, AIAA Journal of Propulsion and Power, 2017.
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[2] Petro, Brieda, and Sedwick, PIC Simulations of Chemistry Effects in an Electrodeless Water Plasma Thruster, Proceedings of AIAA Propulsion and Energy Forum, 2019.
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[3] Petro and Sedwick, Effects of Water Vapor Propellant on Helicon Thruster Performance, Proceedings of AIAA Propulsion and Energy Forum, 2016.
Electric Propulsion and Mission Design
The choice of propulsion system is deeply tied to mission objectives and spacecraft properties. Electric propulsion systems often enable missions that are otherwise infeasible with less fuel-efficient propulsion architectures. For these missions, the propulsion system, spacecraft, and trajectory are closely coupled throughout the formulation and design process. We are interested in exploring new ways that electric propulsion and other revolutionary architectures can enable new solar system science and we are working to develop tools to explore this design space more efficiently.
[1] Petro and Sedwick, Survey of Moderate-Power Electric Propulsion Systems, Journal of Spacecraft and Rockets, Vol. 54, No. 3, 2017.
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[2] Sheerin, Petro, Lozano, and Lubin, Fast Solar System Transportation with Electric Propulsion Powered by Directed Energy, Acta Astronautica, vol. 179, 2021.
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[3] MacKensie, et. al., THEO Concept Mission: Testing the Habitability of Enceladus’s Ocean, Advances in Space Research, Vol. 58, No. 6, 2016.
