SATELLITE WESTPAC INFLUENCE OF THE GRAVITY FIELD ON THE ACCURACY OF ORBIT ESTIMATION

摘要

WESTPAC (Western Pacific Laser Tracking Network Satellite) was launched on July 10, 1998, into a circular orbit at an altitude of 835 km and with an inclination of 98 degrees. To obtain a high-quality orbit solution, the perturbing forces need to modelled as accurately as possible. This paper discusses the influence of the modelling of physical effects caused by conservative forces on the motion of WESTPAC, in particular in terms of orbit quality. The study is based on SLR observations taken by the global network of ground stations during the period from August 1, 1998, until March 30, 1999. In this study, a number of different test cases are defined and investigated. Firsl, the reference scenario is defined, which includes the following main elements: EGM-96 gravity field up to degree and order 70 * 70 (Lemoine et al.,1998) and tidal model, DTM 87 atmospheric density model. The following unknowns were estimated in each scenario: the satellite state-vector for each 8-day arc, atmospheric drag parameters C_D, solar radiation pressure scaling parameters C_R and empirical accelerations in different directions. Alternatively, a number of other scenarios were defined, all of them derived from the reference scenario in which modifications have been made in terms of gravity field and the tidal models. The quality of the orbit solution is assessed by looking at the rms-of-fit.