Drag Coefficient Model Using the Cercignani–Lampis–Lord Gas

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Drag Coefficient Model Using the Cercignani–Lampis–Lord Gas–Surface Interaction Model

Walker, Andrew / Mehta, Piyush / Koller, Josef

Drag coefficient calculations using the Cercignani–Lampis–Lord quasi-specular gas–surface interaction model have been used to derive modified closed-form solutions for several simple geometries. The key component of the modified closed-form solutions is a relation between the normal energy and normal momentum accommodation coefficients, which is valid within $\sim 0.5 %$ over the global parameter space. The modified closed-form solutions are made self-consistent by relating the effective energy accommodation to the partial pressure of atomic oxygen through a Langmuir isotherm. The modified closed-form solutions are compared to fitted drag coefficients and drag coefficients computed using two other gas–surface interaction models: diffuse reflection with incomplete accommodation and Maxwell’s model. Comparison during solar maximum conditions shows that both the diffuse reflection with incomplete accommodation and Cercignani–Lampis–Lord models agree with fitted drag coefficients within $\sim 2 %$ below $\sim 500 km$ altitude. Further comparison shows that solar minimum drag coefficients are up to $\sim 24 %$ higher than those at solar maximum based on global ionosphere–thermosphere model atmospheric properties. Drag coefficients computed with atmospheric properties from the Naval Research Laboratory mass spectrometer incoherent scatter extended model and the global ionosphere–thermosphere model agree within $\sim 2 %$ at solar maximum but disagree by up to $\sim 11 %$ at solar minimum.