Hamza Eren Gunaltay

Air-breathing electric propulsion (ABEP) systems offer a potential solution for sustained spacecraft operations in Very Low Earth Orbit (VLEO), by utilizing atmospheric particles as propellant, thereby reducing dependence on onboard fuel. This work presents the design, feasibility, and orbital performance of the ABEP spacecraft EULO, intended to operate near 200 km with a high resolution optical Earth observation payload. A preliminary 550 kg spacecraft was designed to meet mass, power, and aerodynamic constraints while fitting within a UK based launcher, RS-1. The orbital performance of the satellite was simulated with a high-fidelity propagator coupled with a panel based aerodynamic force estimation method using gas-surface interaction models evaluated at each time step. This geometric framework, compared to a classic cannonball model, enables modelling of thespacecraft’s attitude, which in this study was held constant and either aligned with the orbital velocity or the local flow. Simulations on a generic ABEP spacecraft highlighted that misalignments with the relative flow can significantly affect orbital stability, with some configurations experiencing de-orbiting due to such misalignments. Furthermore, the EULO spacecraft demonstrated sustained a simulated flight at 255 km, achieving a theoretical ground sampling distance of 0.38 m and requiring the intake to have a collection efficiency of 50%. Nevertheless, uncertainties in the aerodynamic modelling suggests that improving thruster performance will be essential to mitigate these uncertainties.

Spacecraft in Very Low Earth Orbit (VLEO) could play a significant role in improving daily life through enhanced communication, Earth observation and environmental monitoring. Their close proximity to Earth enables higher resolution imagery for improved weather forecasting and disaster monitoring, faster data transmission with lower latency, and faster natural deorbiting to ensure compliance with space debris mitigation policies. However, operating at such altitudes poses significant challenges, particularly due to atmospheric drag, and requires active propulsion systems to maintain operational orbits over extended periods. Additionally, Earth's gravity field variations exert greater influence on VLEO satellites. In this research, a high-fidelity orbital propagator is being developed including atmospheric drag effects calculated via simplified Gas Surface Interaction (GSI) models and perturbations from the Earth's non-spherical gravity field and third-body attractions from the Moon and the Sun. Aerodynamic forces acting on the satellite were computed using panellised satellite models, with relative velocity including horizontal neutral winds. The propagator's accuracy was verified using Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) data with GSI parameter's described in the literature, achieving close alignment with GOCE's ephemeris during its free-fall. An air-breathing satellite platform aligned with the orbital velocity vector was tested with the propagator. This alignment, caused deviations in the relative particle velocity vector, resulting in elevated drag. This rendered passive compression systems insufficient to the meet required number density thresholds, necessitating the need for active intake systems. A control methodology was derived from the rate of change of perigee using Gauss Variational Equations which demonstrated improved flexibility and robustness compared to previous methods available in the literature.