The accuracy of orbit estimation for the low-orbit satellites LARETS and WESTPAC

The experience acquired during the orbit estimation of WESTPAC was applied to the orbit investigation of LARETS. The WESTPAC was merely used for reference and initial parameters of the force model [Rutkowska, M., Noomenn, R., Global orbit analysis of the satellite WESTPAC, Adv. Space Res., 30(2), 265-270, 2002]. The orbit of LARETS was estimated with an rms-of-fit to the SLR measurements of 3.9 cm, using the following computation model: the CSR TEG-4 gravity field up to degree and order (200,200), the Ray tide model, the MSIS86 model for atmospheric density [Hedin, A.E., MSIS-86 Thermospheric Model, J. Geophys. Res., 92 (A5), 4649-4662, 1987], and the solution of 8-hourly CD-values. It has been verified that the modeling of the gravity field up to degree and order (100,100) which gives the same rms-of-fit value. Estimated orbits for both satellites are compared to each other in Fig. 2. All computations are performed with the NASA program GEODYN II [Eddy, W.F, McCarthy, J.J., Pavlis, D.E., Marshall, J.A., Luthce, S.B., Tsaoussi, L.S., GEODYN II System Operations Manual, vol. 1-5, ST System Corp., Lanham MD, USA, 1990].