Design and optimisation of a passive Atmosphere-Breathing Electric Propulsion (ABEP) intake

In order to extend the orbital lifetime of spacecraft operating in Very-Low Earth Orbit (VLEO), Atmosphere-Breathing Electric Propulsion (ABEP) can be employed for atmospheric drag compensation. The concept is based on the ingestion of rarefied atmospheric particles to be used as propellant for an electric thruster, thereby removing the need for onboard propellant. The present paper aims to design and analyse a passive ABEP intake optimised for the RF Helicon-based Plasma Thruster (IPT), which is selected as the most promising system due to its electrodeless design, as it removes the issue of thruster corrosion, and reduced susceptibility to atmospheric variations. This is achieved by implementing the analytical model, referred to as the Balancing Model (BM), along with its main performance parameters. The Direct Simulation Monte Carlo (DSMC) solver dsmcFoam+ is thus employed to simulate the transmission probability of cylinders and hexagonal prisms with non-zero entrance velocity, yielding a mean percentage error of 2% when compared to independent DSMC results. In addition, a novel DSMC transmittance investigation of square prisms is performed. Various design configurations are optimised for circular and hexagonal intakes based on the functional requirements of the thruster, leading to a maximum collection efficiency of 45% for a cylindrical intake with a hexagonal honeycomb. The optimal intake is hence simulated via DSMC, showing a good accuracy with the BM with or without intermolecular collisions, yielding a percentage error of 0.22% in the former case and 5.53% in the latter one. The variation of incidence flow angle, accommodation coefficient and thruster transmission probability is finally investigated, and the results are validated by the agreement shown with values retrieved from the literature.