A Generalized Model of Drag Coefficient Using Hybrid Gas-Surface Interaction

Accurate calculation of drag coefficients is critical for improving atmospheric drag-related applications and depends heavily on the proper specification of the gas-surface interactions (GSI). Two commonly used GSI models are the Diffuse Reflection and Incomplete Accommodation (DRIA) model and the Cercignani-Lampis-Lord (CLL) model, along with constant or variable accommodation coefficients. The DRIA model assumes a diffuse reflection, making it more appropriate for lower thermospheric conditions dominated by atomic oxygen, while the CLL model assumes quasi-specular interactions, better suited for the helium-dominated upper thermosphere. Prior studies have shown that the performance of these models varies with thermospheric density and composition as well as satellite surface properties. To address these limitations, we explore hybrid DRIA–CLL formulations, incorporating variable accommodation model in order to define a generalized model of gas-surface interactions that is applicable across a wide range of atmospheric conditions. This study compares several such hybrid models—both existing and newly proposed—against the baseline DRIA and CLL models, evaluating their accuracy in estimating drag coefficients through satellite conjunction analysis.