Effects of atmospheric winds and aerodynamic lift on the inclination of the orbit of the S3-1 satellite

Aerodynamic drag and lift effects on the inclination of the orbit of the S3-1 satellite have been used to infer atmospheric zonal wind speeds at an altitude of 175 km and to estimate the satellite surface thermal accommodation coefficient. The unusually high quality of the orbital and attitude data permitted the 7-month data span to be analyzed in 6 non-overlapping subintervals, thereby resulting in finer local-time and spatial resolution than is normally obtained in such studies. The aerodynamic lift force was found to be quite sensitive to the assumed value of the thermal accommodation coefficient, a quantity that is neither well known nor understood. The inclination data were best fit (in a least squares sense) when the accommodation coefficient was greater than 0.95. Best agreement with theoretical models in terms of wind speed and direction was obtained when the accommodation coefficient was taken to be nearly 1.0. In this case, the inferred wind was 400 m/sec eastward at local times 19-21 hr, and 200 m/sec westward at local times 7-9 hr. The study indicates that if accurate zonal wind velocities are to be derived from satellite orbital inclination changes, care must be taken to ensure that the shape and orientation of the satellite are such that the lift forces generated are sufficiently small that the resulting uncertainty due to inadequate knowledge of the accommodation coefficient does not cause significant error.