Thermal Force Modelling for Precise Prediction and Determination of Spacecraft Orbits

The physical modeling of nonconservative forces is a limiting factor in orbit prediction. One such force arises from the anisotropic emission of thermal radiation from a satellite's surface, which can perturb a spacecraft trajectory significantly. Hence a thermal analysis is crucial for precise analytical force modeling. This paper presents the authors' approach to thermal force modeling, using GPS Block IIR and the altimetry satellite Jason-1 as test cases. The treatment of spacecraft multilayer insulation, solar panels, and other spacecraft components is described. A novel approach to determining eclipse boundary crossing times for an oblate earth and the characterization of penumbral flux are discussed. The GPS Block IIR models are tested by incorporation into a high-precision radiation pressure model developed at University College London. Orbit predictions show significant improvements with inclusion of the thermal models. The Jason-1 models have been incorporated into the routine orbit determination of Jason-1 by the Jet Propulsion Laboratory.