Crandall, P., Wirz, R.E., “Air-breathing electric propulsion: mission characterization and design analysis.,” J Electr Propuls 1, 12 (2022); https://doi.org/10.1007/s44205-022-00009-8

Air breathing electric propulsion (atmosphere-breathing electric propulsion) (ABEP) has attracted significant interest as an enabling technology for long duration space missions in very low Earth orbit (VLEO) altitudes below about 300 km. The ABEP spacecraft and mission analysis model developed allows parametric characterization of key spacecraft geometry and thruster performance parameters such as spacecraft length-to-diameter, the ratio of solar array span to spacecraft diameter, thrust-to-power, effective exhaust velocity, and inlet efficiency. For the missions analyzed ABEP generally outperforms conventional electric propulsion (EP) below 250 km altitude. Using a 6U spacecraft architecture the model shows that below 220 km ABEP is the only viable propulsion option for desirable mission lifetimes. Parametric evaluations of key spacecraft and ABEP characteristics show that the most significant technological improvements to ABEP spacecraft performance and range of applicability for VLEO missions will come from advancements in inlet efficiency, low drag materials, solar array efficiency, and thrust-to-power.

Crandall, P., Wirz, R.E., “P. Crandall, and R.E. Wirz, "Miniature RF Gridded Ion Thruster For Air-Breathing EP,” IEPC (2024)

P. Crandall, V. Piccone, T. Asanuma and R. E. Wirz, “Geomagnetic Storm Risks to Air-Breathing Electric Propulsion Missions,” IEEE Aerospace Conference (2024); 10.1109/AERO58975.2024.10520952

Geomagnetic storms can cause significant and rapid increases in atmospheric density at very low Earth orbit (VLEO) altitudes potentially putting a VLEO spacecraft into an un-recoverable orbit. Air-breathing electric propulsion (ABEP) spacecraft may be more susceptible to geomagnetic storms due to the low thrust-to-drag chosen for many proposed spacecraft. For ABEP missions to become viable, risks due to geomagnetic storms must be mitigated. This work explores geomagnetic storm risks to ABEP spacecraft using an orbit propagator. Spacecraft with low ballistic coefficient and low thrust-to-drag are identified as highly susceptible to geomagnetic storm risks. Two risk mitigation strategies are investigated for these space-craft: (1) preemptive orbit raising ahead of a storm, and (2) using onboard xenon propellant to increase thruster performance during a storm. An orbit propagator is used to investigate performance of these risk mitigation strategies during a G4 (severe) geomagnetic storm in November 2004. It is shown that preemptive orbit raising successfully mitigates geomagnetic storm risks for spacecraft with higher thrust-to-drag while adding a relatively small amount of xenon propellant mitigates geomagnetic storm risk for all spacecraft.

Crandall, P., Cretel, C., Wirz, R., “RF Gridded Ion Thruster Design for Laboratory Experiments,” AIAA SCITECH 2024; PDF, https://doi.org/10.2514/6.2024-1549

RF gridded ion thrusters are simpler in construction than other gridded ion thrusters and have been shown to be more robust for air-breathing electric propulsion and alternative propellant applications than DC thrusters. ICP sources can be difficult to construct for new users who are unfamiliar with RF systems limiting adoption of RF thrusters. This work presents a basic overview of RF ion thruster concepts, ICP operating principles, antenna matching, and thruster design for new users. A lab model RF gridded ion thruster developed at the UCLA PESPL is described as a design example and preliminary performance values are presented.

Crandall, P., Wirz, R., “Air-Breathing Electric Propulsion Spacecraft Performance and Aerodynamic Maneuverability,” IEPC 2024; PDF

Air-breathing electric propulsion (ABEP) has the potential to enable long duration missions in very low Earth orbit (VLEO). This work presents a mission analysis model which predicts ABEP minimum operating altitude and thrust-to-drag (T/D) as a function of spacecraft bus geometry and thruster performance metrics. Aerodynamic lift created from spacecraft yaw is investigated and the spacecraft lift-to-drag ratio is reported. It is determined that aerodynamic maneuvers are not viable for high accommodation coefficient materials, and low accommodation coefficient materials significantly improve lift-to-drag.