Numerical investigation of critical aspects for the intake of atmosphere-breathing electric propulsions for VLEO applications

The capacity to collect and adequately compress the incoming hyperthermal flow is crucial to the improvement of the design of air-breathing propulsion systems. Since this technology aims at the lower range of the Very Low Earth Orbits (VLEO), the drag to compensate is another determining design factor. In this context, the Direct Simulation Monte Carlo method can help shed light on the crucial aspects for the intake design of this propulsion concept and enhance further development towards the on-ground or in-orbit testing. This computational method is suitable for low-density hyperthermal flows, and it allows the gas-surface interaction modelling, which is paramount for the correct description of the interaction between the wall and the rarefied flow in the free-molecular regime. Assuming a partially diffuse re-emission, the impact of the gas-surface interaction model on the drag and other performances is evaluated for three altitudes 150, 180, 210 km and the results yielded by the widely adopted Maxwellian reflection model are compared to the ones obtained with the Cercignani–Lampis–Lord model, which has been extensively adopted for VLEO satellite drag estimation but more rarely for air-breathing electric propulsion intake studies. Finally, for the mid-altitude of interest, 180 km, the impact of the angle of attack variation (0°–20°) on the collection and compression efficiency is evaluated to identify the propellant delivery limitation, which can result in the electric thruster ignition failing.