Direct and indirect charged aerodynamic mechanisms in the ionosphere

Objects in a flowing plasma may exchange momentum both directly, through gas-surface interactions, and indirectly, through field effects. Applying a control surface approach developed in the study of dusty (complex) plasmas, this work outlines a framework for investigating the relative contribution of direct and indirect charged aerodynamic forces that may arise from the aerodynamic interaction of LEO objects with the ionosphere i.e. ionospheric aerodynamics. In particular, this work focuses on plasma interaction phenomena described by the scaling parameters αk and χ, which describe the ratio of body potential energy to ion kinetic energy and the ratio of body size to sheath thickness respectively. Ion kinetic dominated flows (αk≪1) were found to be well approximated by neutral aerodynamic treatments, the charged drag coefficient (CD,C) of a long (2D) cylinder with a diffusely reflecting surface with complete thermal accommodation to a 500 K wall calculated as 2.232. Body potential dominated systems (αk≫1), however, were dominated by indirect charged aerodynamic mechanisms, an example being the indirect thrust required to balance the sheath driven acceleration of ions through the fore-body sheath, which caused an 82% reduction in net charged drag for the αk=16.9 case. This drag reduction was partially offset by indirect drag forces caused by the deflection of non-colliding ions, the net CD,C being 7.741 for the αk=16.9. A similar study of the relative sheath thickness, described by χ, saw asymptotic behaviours given a constant αk of 1.072; direct charged drag forces becoming either Orbital Motion Limit (OML) for thick-sheath systems (χ→0) or sheath-limited (χ≫1). These results demonstrate the importance of accounting for both direct and indirect charged aerodynamic forces when studying ionospheric aerodynamics, while also providing new physical insights into physical mechanisms momentum exchange processes between a flowing plasma and immersed object.