Investigation of Gas‐Surface Interactions and Neutral Atmospheric Properties and Their Impact on Satellite Drag Coefficients

Abstract Changes in the thermospheric composition and temperature influence satellite drag coefficients through functional dependencies in the closed‐form solutions, and gas‐surface interactions via accommodation coefficients. This study investigates drag coefficient variations for the Gravity Recovery And Climate Experiment (GRACE) and Communications/Navigation Outage Forecasting System (C/NOFS) satellites under varying atmospheric conditions and satellite orientations. The closed‐form solutions of Diffuse Reflection and Incomplete Accommodation (DRIA) and Cercignani‐Lampis‐Lord (CLL) gas‐surface interaction models have been used to calculate the drag coefficients. The momentum and energy accommodation coefficients, derived using empirical models, are used as input variables in the closed‐form solutions to specify the nature of the gas‐surface interactions. The results provide a realistic view of drag coefficient variations for the atmospheric changes observed for low‐Earth orbit satellites. The analysis reveals that increasing the atomic oxygen mole fraction leads to significant decreases in the drag coefficients, with CLL showing greater variability than DRIA. The variability of the drag coefficients with neutral temperature demonstrates a strong dependence on satellite shapes, with GRACE drag coefficients increasing with temperature while C/NOFS drag coefficients decrease. Analysis of the C/NOFS orbits demonstrates drastic changes in the gas‐surface interactions, transitioning from oxygen‐dominated diffuse scattering at lower altitudes to helium‐dominated quasi‐specular interactions at higher altitudes. These variations persist during the September 2011 geomagnetic storm, with slightly reduced drag coefficients during storm‐time conditions compared to quiet periods. The GRACE drag coefficients are highly sensitive to pitch and yaw angle variations, while the C/NOFS drag coefficients show minimal sensitivity due to its more symmetrical geometry.