Atmosphere-breathing electric propulsion (ABEP) is a type of electric propulsion system that uses the atmosphere as a propellant source instead of a stored reservoir. This technology is still in its early stages, but holds the promise of providing a clean, efficient, and sustainable propulsion system for spacecraft, enabling very low Earth orbit (VLEO) mission scenarios. To optimise the ABEP technology, accurately simulating air-based plasma chemistry plays a crucial role. In this paper, an air-based global model (GM) is presented that includes a detailed chemistry model for the various reactions that are involved in ABEP applications. The model’s goal is to forecast the performance of a cathode-less RF plasma thruster under various pressure levels and species concentrations that are typical of VLEO missions. The GM was exploited to map the performance of a fictitious ABEP based on a cathode-less RF thruster in order to assess its feasibility in VLEO. The numerical model is promising as a tool for the design of ABEP systems and for the preliminary optimization of mission scenarios.

This study investigates the preliminary propulsive performances of a cathode-less plasma thruster with air as its propellant. The analysis is carried out through a global model and simulates a thruster over a power range of 0 to 50 W. The developed code considers a set of 177 chemical reactions involving 8 different species and includes empirical equations to account for electronegative effects. The analysis presents the steady-state values of species densities at 10 W, 30 W, and 50 W to gain insights into the key characteristics of plasma dynamics. Moreover, the study estimates the thrust and specific impulse and compares the results to data from models that employ xenon and iodine, aiming to understand the performances of air in low-power thrusters. Lastly, the study examines the effects of varying air inflow concentration on the chemistry, analyzing three different orbit altitudes (i.e., 200, 300, and 400 km).

Magnetic nozzles (MNs) are known to be subject to anomalous non-collisional diffusion mechanisms driven by instabilities and wave-particle interactions. This study therefore employs a fully kinetic axial–radial particle-in-cell model to examine the impact of this anomalous diffusion on plasma transport and the propulsive performance of MNs typical of low-power cathode-less radio-frequency plasma thrusters. A Bohm-type anomalous collisionality scaling ( ν an = α an ω c e ) is implemented to simulations of the 150 W-class REGULUS-150-Xe thruster, evaluating both low-power (30 W) and high-power (150 W) operating conditions. The impact on azimuthal electron current formation is assessed, as well as its subsequent effect on thrust generation, momentum and power balance, and overall propulsive efficiency. A transition region of Bohm coefficient was found to exist, where the MN expansion evolves from a well-collimated to an under-collimated state and electron transport shifts from being dominated by magnetic advection to being dominated by cross-field diffusion. This was found to occur within a narrow interval between α an = 1/128 and 1/32. Beyond this transition, it is found that the enhanced cross-field transport of electrons inhibits the formation of the typical MN potential barrier, reducing the radial confinement. The downstream potential drop is reduced by up to 15%. Diamagnetic electron current is diminished in the absence of steep pressure gradients and the E × B current becomes purely paramagnetic. The MN efficiency is cut from circa 0.5 to 0.2 due to loss of electron thermal energy conversion and increased plume divergence. At the Bohm limit of α an = 1 / 16 , agreement to experimental thrust profiles of < 20% is achieved in contrast to 48% overestimation at high-power in the classical case.