Modelling the anomalous acceleration and radiation pressure forces for the TOPEX/POSEIDON spacecraft

A few months after launch of the TOPEX/POSEIDON (T/P) spacecraft, during the verification phase of the mission, the Precision Orbit Determination Team discovered residual along–track accelerations which were unexpected and of unknown origin. This paper describes the analysis of radiation forces acting on the T/P spacecraft for the purpose of understanding and providing an explanation for the anomalous accelerations. The radiation forces acting on the solar array, which experiences warping due to temperature differences between the front and back surfaces, are analysed and the resulting along–track accelerations are determined. This analysis led to the development of a new radiation force model which includes (1) warping of the solar array, (2) solar array deployment deflections as large as 2°, (3) necessary adjustments to certain surface property parameters, and (4) an adjustment to the coefficient of drag. As a result of the new model, estimates of the empirical constant along–track acceleration are significantly reduced in magnitude and are less dependent upon the location of the Sun relative to the orbit plane.