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Experimental investigation of ionospheric aerodynamics effects

The accurate prediction of the motion of resident space objects (RSOs) in Low Earth Orbit (LEO) requires knowledge of all forces acting on these objects, which includes active and inactive (e.g. debris) objects. In this context, charged particle interactions with RSOs and associated orbital perturbations resulting from charged aerodynamic effects, i.e. momentum exchange between the ambient plasma and the RSO, are currently poorly understood and typically neglected. This paper presents results from an experimental investigation aimed at quantifying the net force imposed on a charged test object subjected to a 5 eV streaming Ar+ plasma representative of the plasma-body interaction experienced by RSOs orbiting within the ionosphere in LEO. In addition to net charged force measurements, the ion current collected by the charged test object was recorded. An increase in force with increasing negative test object surface potential was measured, in accord with numerically predicted behavior. Differences in the trends for the force and current measurements were observed with increasing negative test object surface bias. This can be attributed to indirect ion momentum exchange resulting from the electrostatic interaction between the streaming ions and the electrostatic sheath surrounding the charged test object. This indirect force acts to reduce the direct charged force (from ions hitting the surface) imparted on the charged test object. Numerical reconstruction of the experiments using an in-house PIC code showed very good good agreement with the experimental current data but could not accurately resolve the trend for the net charged forces with increasing test object surface bias. Further work is currently ongoing to understand and resolve this discrepancy.