Additive Manufacturing of Hall Thrusters

From low Earth orbit mega-constellations such as Starlink and OneWeb, to space stations like the Lunar Gateway and Tiangong, and extending to deep space missions such as Psyche, Hall thrusters have emerged as the dominant electric propulsion (EP) system today. Their widespread adoption is driven by an optimal balance between thrust density and specific impulse combined with a robust and relatively simple design. While mid-power Hall thrusters are considered mature compared to other EP systems, significant challenges remain in scaling to both high- and low-power regimes, in using alternative propellants, in achieving high power densities, and in manufacturing for large constellations. Additive manufacturing (AM) of metals and ceramics introduces a paradigm shift in addressing these challenges, offering unprecedented design freedom and production efficiency. This thesis pioneers its application to Hall thrusters, focusing on magnetic circuits and propellant distribution and injection systems, while establishing a cost-effective in-house metal AM process at the University of Pisa. The research is structured into three key parts. The first examines the state of the art in AM for electric propulsion, assessing its advantages, limitations, and applicability to magnetic circuits and propellant distributors. The second part presents a study on the Material Extrusion Additive Manufacturing of Metals (MEX-M), based on the extrusion, debinding, and sintering of polymeric feedstocks highly filled with metal powders. Two base materials were investigated: Inconel-718 for fabrication of anode-distributors and soft iron for magnetic circuits. By optimizing feedstock formulation and processing parameters, the research achieves soft iron components with about 90% relative density and 80% of the saturation magnetization of pure iron, alongside Inconel components with 96% relative density and mechanical properties comparable to those obtained via Laser Powder Bed Fusion (LPBF), all while preserving complex geometries and with fractional cost compared to other metal AM techniques. The final part of the dissertation presents two case studies. The first demonstrates the design and fabrication of a Hall thruster magnetic circuit via MEX-M and the validation of its performances through magnetic field mapping using a custom-built system. The second showcases the design and production of the two anode distributors for the 20 kW TANDEM dual-channel Hall thruster using LPBF. AM enabled a 60% cost reduction, a 90% decrease in lead time and welding seam length, and the integration of all parts into one main component with respect to the previous design, while also maintaining state-of-the-art azimuthal flow uniformity. TANDEM is the first thruster in the world that successfully operated AM-anodes at power levels up to 25 kW using krypton and xenon while maintaining state-of-the-art propulsive performance. Ultimately, this work marks a significant milestone in electric propulsion research, offering the first systematic investigation into MEX-M for Hall thrusters and proving AM’s transformative potential for next-generation EP systems. Furthermore, it lays the foundation for rapid, cost-effective, in-house production of critical thruster