Modelling and design optimisation of a hollow cathode thruster

Abstract

The present trend in spacecraft is to have two separate thrusters systems performing different tasks, a main electric propulsion system operating on xenon and a chemical system, usually bipropellants or cold gas. The development of a low power electric propulsion system
operating on xenon to replace the chemical thrusters on board spacecrafts would be beneficial. It would be bring significant advantages in terms of mass saving from the sharing of the tanks, pipes and flow control unit, also with improvements in the specific impulse.

In recent years experiments have demonstrated the possibility of using hollow cathodes as standalone thrusters, with indirect thrust measurement performed at the University of Southampton. Nevertheless indirect thrust measurements bring large uncertainties on the real value of the thrust. For the first time, direct thrust measurements were carried out with two different thrust balances on two different hollow cathode thrusters, derived from the T5 and T6 hollow cathodes, with unique design modification in the orifice and anode geometry. These measurements provide a
unique insight into the real performance range of hollow cathode thrusters. Significant improvements in thrust, specific impulse and thrust efficiency have been achieved thanks to the optimized design of the T6 hollow cathode.

The design of the thruster was modified using a one dimensional theoretical model developed within this research. With the help of the theoretical model the optimisation of the hollow cathode thruster design was carried out and a better understanding of the physical mechanisms which contribute to the generation of the thrust could be achieved, with the conclusion of electrothermal
and electromagnetic phenomena being the main contributors. The main conclusions of the research and recommendations for related future works are also presented.

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