Abstract
Progress in spacecraft technology ranges from mega-constellations aimed at communication services to deep space missions targeting lunar and beyond exploration, all facilitated by small and micro satellites. Hall thrusters, with their high thrust density, reliable performance, simple design, and proven spaceflight heritage, are well suited for these missions.
Miniaturising Hall thrusters for low-power applications with long lifetimes and high efficiency poses considerable challenges, largely due to the high surface area-to-volume ratio
and the physical limitations involved in scaling down the magnetic circuit.
This thesis investigates a novel concept that expands the total utilised cross-sectional area of the Hall thruster by removing the channel walls and sustaining the plasma discharge
entirely outside the thruster chassis. This channel-less technology offers benefits such as a reduced thruster mass and the elimination of plasma-wall interactions. A 200 W miniaturised External Discharge Plasma Thruster (mini-XPT), featuring a channel-less design, is developed and characterised using xenon and krypton. This research identified the limitations and performance loss mechanisms that are inherent in this thruster design. A novel hollow cathode prototype featuring a modular design is also developed to support ground testing of the channel-less plasma thruster. This cathode, which includes a keeper disk, an orifice disk, and direct emitter heating, has been systematically tested under various operational conditions. The influence of the modular hollow cathode position and operating parameters on the mini-XPT performance is also assessed, revealing that the cathode position and operating mode significantly influence the performance. Plasma properties measured via a Langmuir probe reveal how the plasma potential decreases and the electron density increases in the coupling region with additional heating and higher mass flow rate. This contributes to the observed performance improvements. Finally, an auxiliary anode is used to enhance the thrust by focusing ions axially, demonstrating a trade-off between the current utilisation efficiency and the ion directional acceleration.