Aerodynamic Performance Characterization and Geometry Optimization of Satellite Control Surfaces in Very Low Earth Orbit

Very Low Earth Orbit (VLEO) refers to altitudes ranging from the Kármán Line up to approximately 400 km. Interest in VLEO has surged in recent years due to its unique advantages, such as enhanced imaging resolution, improved radar communications, reduced launch and operational costs, and self-cleaning orbits that help mitigate space debris accumulation. However, VLEO environments present considerable challenges for satellite operations. In this region, the high density of atomic oxygen accelerates surface degradation and increases unpredictability from particle impacts. The denser atmosphere relative to LEO also causes substantial aerodynamic drag, leading to complex interactions that remain challenging to model, especially regarding particle re-emission from surfaces. In VLEO, adding surface elements to utilize aerodynamic forces can provide effective control over satellite attitude and orbit. Given the high-speed flow, flat plates may initially appear effective for satellite maneuvering. However, as flow regimes shift from rarefied to continuum, this geometry may not provide optimal maneuvering efficiency. To further investigate the interactions between gas and surface, the von Karman Institute developed the DRAG-ON facility to replicate VLEO conditions on Earth. This study’s first objective is to characterize the forces generated by rarefied and ionized flows on an inclined flat plate within this facility. The model considers pressure contributions from high-speed atoms and ions, excluding electrons. Depending on the accommodation coefficient, some particles adhere and diffuse across the surface, while others reflect specularly. These pressures are then integrated over the plate surface to determine axial and normal forces based on the plate’s incidence angle. To validate this model, advanced tools are used: SMARTA, a view-factor-based software, and SPARTA, a Direct Simulation Monte Carlo (DSMC) tool. The second objective of this thesis is to investigate how the optimal geometry for maximizing aerodynamic efficiency in VLEO changes as altitude decreases and the flow transitions between free molecular and continuum regimes. Using SPARTA, aerodynamic forces are assessed starting from a flat plate baseline and introducing a hinged plate design to explore how an additional degree of freedom affects the lift-to-drag ratio. This study identifies the altitude threshold at which intermolecular collisions occur due to sufficient local particle density around the hinged plate, leading to deviations from the free molecular flow analytical model. Simulations reveal that the optimal angle of attack for a flat plate configuration changes with altitude variations. While a flat plate maximizes lift-to-drag ratio and lift coefficient in free molecular flow, its efficiency can decrease at lower altitudes as a function of the accommodation coefficient. Based on these results, the study pinpoints when surface curvature and varying accommodation coefficients create optimal conditions for spacecraft control and operational longevity in VLEO.