Orbit analysis of the satellite westpac Original Research Article

This paper addresses the computation of the orbit of the satellite WESTPAC, which 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, all forces acting on the satellite need to be modelled as accurately as possible. This paper discusses the influence of the modelling of different physical effects on the motion of WESTPAC, in particular in terms of orbit quality. The study is based on observations taken by the global network of laser stations during the period from August 1, 1998, until March 30, 1999. In this study, a number of test cases are defined and investigated, focussing on optimum orbit quality. The latter is assessed by looking at the (weighted) rms-of-fit, the orbit overlaps of successive data arcs and the stability of independent solve-for parameters. The investigation has resulted in a “best” scenario which includes the following elements: the GRIM-5S1 gravity field solution, the MSIS86 model for atmospheric density, the GOT99.2 ocean tides model, drag coefficients solved-for at 12-hour intervals, and one set of 1-cpr accelerations in the along-track and cross-track directions. This scenario gives a fit of the laser range observations of 3.7 cm and an orbit quality of about 5, 10 and 20 cm in the radial, cross-track and along-track directions, respectively.