Solar activity dependency of a specular intake for an ABEP system

Abstract Challenging space missions at very low altitudes face significant atmospheric drag, requiring efficient propulsion methods such as Atmosphere-Breathing Electric Propulsion (ABEP) to extend mission lifetimes. ABEP captures atmospheric particles and uses them as propellant for an electric thruster, reducing dependence on limited on-board propellant. This could extend missions in Very Low Earth Orbit (VLEO) and on celestial bodies with an atmosphere, such as Mars. The Institute of Space Systems (IRS), under the EU H2020 DISCOVERER, ESA Ram-CLEP, and CRC ATLAS projects, is developing a high-efficiency specular intake and a RF Helicon-based plasma thruster (IPT) for ABEP. This study uses the numerical tool PICLas and it’s Direct Simulation Monte Carlo Method’s (DSMC) to analyse the effect of solar activity and evaluate the validity of the hyperthermal assumption in VLEO for ABEP intake designs. Additionally, the effect of changing intake lengths on important key parameters, such as intake efficiency, mass flow rate, and pressure, is examined. The results show that efficiency decreases with higher solar activity, longer intakes and higher altitudes, with particle temperature having the greatest effect on efficiency, due to its influence on thermal velocity and the molecular speed ratio. An almost linear relationship between efficiency and molecular speed ratio is shown, revealing that the hyperthermal assumption may not be valid for VLEO applications. To achieve the required pressure level for ignition, flexible ABEP operation is recommended to accommodate for varying solar activity, suggesting lower altitude operation during low solar activity and higher altitude operation during high solar activity.