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In Hall propulsion systems, a direct and non-isolated connection between the thruster discharge and the solar array implies a significant change in terms of spacecraft grounding, thruster operation and control. In this so-called direct-drive architecture, since discharge voltage and current are no more fixed by a power processing unit but are constrained by the solar array characteristic, which changes during a space mission, specific control laws need to be developed and tested to assess the feasibility of thruster operation. In this paper, in-depth investigations performed in SITAEL on thruster performance and operation controllability of a direct-drive Hall thruster system are presented. The HT5k, a 5 kW-class Hall thruster, was connected to a solar array simulator (SAS) and tested at different operating conditions. Three different thruster control laws were implemented and were proved effective in controlling the thruster behavior with respect to on-orbit-representative variations in the SAS characteristics. The results also highlighted minimal difference between thruster performance parameters in direct-drive and with a conventional power supply. Finally, the impact of grounding on thruster plume interaction with the spacecraft was analyzed.

One of the main oscillatory modes found ubiquitously in Hall thrusters is the so-called breathing mode. This is recognized as a relatively low-frequency (10–30 kHz), longitudinal oscillation of the discharge current and plasma parameters. In this paper, we present a synergic experimental and numerical investigation of the breathing mode in a 5 kW-class Hall thruster. To this aim, we propose the use of an informed 1D fully-fluid model to provide augmented data with respect to available experimental measurements. The experimental data consists of two datasets, i.e., the discharge current signal and the local near-plume plasma properties measured at high-frequency with a fast-diving triple Langmuir probe. The model is calibrated on the discharge current signal and its accuracy is assessed by comparing predictions against the available measurements of the near-plume plasma properties. It is shown that the model can be calibrated using the discharge current signal, which is easy to measure, and that, once calibrated, it can predict with reasonable accuracy the spatio-temporal distributions of the plasma properties, which would be difficult to measure or estimate otherwise. Finally, we describe how the augmented data obtained through the combination of experiments and calibrated model can provide insight into the breathing mode oscillations and the evolution of plasma properties.

We performed a test campaign in order to fill the gaps in the experimental data and understanding of the performance of the Applied Field Magnetoplasmadynamic Thruster in low current, high mass flow rate regime. Thrust and discharge voltage were measured for two anode geometry configurations with different mass flow rate distribution, discharge current and external magnetic field strength. The general trends in thruster behavior using argon as propellant are analyzed in this paper and an approach for thruster optimization is investigated. We find an unexpectedly weak dependence of thrust efficiency on discharge current in low current, high mass flow rate regimes. Using a cylindrical anode configuration, we managed to achieve thrust efficiency of 21%, which is significantly higher than that reported in literature for AF-MPDTs operating in this regime.