Drag coefficient model using the Cercignani-Lampis-Lord gas-surface interaction model

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 ∼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 ∼2% below ∼500 km altitude. Further comparison shows that solar minimum drag coefficients are up to ∼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 ∼2% at solar maximum but disagree by up to ∼11% at solar minimum.