Application of a satellite aerodynamics model based on normal and tangential momentum accommodation coefficients

Tangential and normal momentum accommodation coefficients are reviewed as a parametrization of the gas-surface interaction for modelling aerodynamic forces on artificial Earth satellites. By reference to experimental data and other studies, a simple empirical relationship for the normal momentum coefficients, σ', is deduced whilst the tangential coefficient, σ, is taken to be invariant with the angle, ξ, between the incident stream and the surface normal. Parameters within these coefficients are estimated by least-squares reduction of orbital elements of ANS-1 (1974-70 A). Derived results are σ = 0.93 and σ' = 1.11-0.17sec ξ, yielding a drag coefficient for a sphere of 2.05 ± 0.03, which is less than 10% below the accepted values of 2.2 for heights near 300 km.