Lessons learnt from operating the first Cubesat mission equipped with a Hall thruster

Only a few electric propulsion solutions on-board small satellites have been operated in space, even if propulsion is nowadays seen as one of the most important subsystems for the future of small satellites. Exotrail demonstrated its Hall Effect Thruster propulsion solution in space at the end of 2020. It was the first Hall thruster ever flown onboard a satellite weighing below 100kg of mass, while also being the only known permanent magnet Hall Thruster demonstrated in space. Operations of small satellites with propulsion is a novel field and the behavior of such thrusters in space still brings new challenges. Exotrail developed its ExoMGTM propulsion system demonstrator between November 2018 and September 2019, when the flight model was delivered to the small satellite manufacturer NanoAvionics. The satellite was eventually launched in November 2020 and following the commissioning of the platform, the thruster was conditioned and subsequently fired. These two last steps will be detailed. The propulsion system consists of the propellant storage and regulation system, the control and power electronics, the actual thruster consisting of an anode and a cathode and a mechanical and thermal interface. It is operated through Exotrail’s ExoOPSTM Operations software. The different subsystems will be described as well as their interaction. Each of them has many observables that will be detailed and discussed – typically temperatures, voltages. The operations software enables the monitoring of the orbital parameters, the maneuver generation, the housekeeping of the propulsion unit and the preparation of the maneuvers. It will be briefly described as it is the main software tool to understand the behavior of the thruster. The commissioning operations of the propulsion unit are firstly focused on health check and controllability of the environmental parameters. Then a health check of the active parts of the propulsion is performed. Finally, the firing sequence is initiated. The different steps, the expected and actual results will be presented and discussed. Finally, we will present the performance estimation of our propulsion unit. Thanks to our on-board GPS data, we perform maneuver restitution and we compare the in-flight performance with ground tests. DESCRIPTION OF THE PROPULSION UNIT Electric propulsion for small satellites The propulsion subsystem for a satellite is critical to deliver high quality services. Propulsion have historically been falling in three categories: solid, liquid and electrical. The first type of propulsion, solid motors, are mainly used to provide short and powerful boosts [1]. This technology is used for rockets, but also for high-ΔV impulsive maneuvers. Liquid propulsion is the most used in the satellite industry [2]. Liquid thrusters rely on a one or more liquid propellants to generate gas in a nozzle and provide a thrust. Complex bi-propellant thrusters are used to perform orbit raising and simpler monopropellant thrusters are used for station-keeping and other low-ΔV maneuvers [3]. Finally, electrical propulsion, though used for a long time on Russian satellites, emerged in the last two decades as the breakthrough in propulsion both for orbit raising and station-keeping, but also for interplanetary missions [4] [5]. The main advantage of electric propulsion is its high fuel efficiency with its specific impulse in the range of 500 to 5000 seconds. However, the achievable thrust with those systems is typically orders of magnitude lower than their solid or liquid counterparts. It produces thrust by