THERMAL FORCE MODELING FOR GLOBAL POSITIONING SYSTEM SATELLITES USINGTHE FINITE-ELEMENT METHOD

Geophysical applications of the Global Positioning System (GPS) requir e the capability to estimate and propagate satellite orbits with high precision. An accurate model of all the forces acting on a satellite i s an essential part of achieving high orbit accuracy. Methods of analy zing the perturbation due to thermal radiation and determining its eff ects on the long-term orbital behaviour of GPS satellites are presente d. The thermal imbalance force, a nongravitational orbit perturbation previously considered negligible, is the focus of this paper. The Eart h's shadowing of a satellite in orbit causes periodic changes in the s atellite's thermal environment. Simulations show that neglecting therm al imbalance in the satellite force model gives orbit errors larger th an 10 m over several days for eclipsing satellites. This orbit mismode ling can limit accuracy in orbit determination and in estimation of ba selines used for geophysical applications.