Satellite Orbit and Ephemeris Determination using Inter Satellite Links

Orbit ComputationInter Satellite LinksRadial [m] Along Track [m] Cross Track [m]7 x 7 0 0 05 x 5 0 0.01 02 x 2 6.2 14.8 0.8J2-Propagator (2 x 0) 4.4 18.5 0.7Kepler (0 x 0) 786 763 0.3JGM-2 (70 x 70) 0 0 0GEM-T3 (50 x 50) 0.44 0.58 0GRIM4-S4 (66 x 66) 0.26 0.3 0Deviated JGM-3 0 0 0Table 4-10 GEO 6 hoursAnother interesting fact is that the model uncertainties are negligible, especially if comparedto the LEO orbit. This is due to the fact that the uncertainties of the lower order harmonicscompared to their magnitude are far smaller than those of the higher order harmonics.It is clear that the GEO orbit, due to the fact the it has a non inclined orbit and see's always thesame part of the gravity field is subjected to extreme low perturbation from the higher orderharmonics. A more general class of orbits, the inclined geosynchronous orbit (IGSO) has thesame revolution period (and therefore orbit altitude) as the GEO. The error introduced to anIGSO orbit by neglecting higher order harmonics shows similar tendencies as for the GEOorbit. The IGSO is slightly more affected by tesseral and sectorial harmonics than the GEO,due to its inclined orbit. But also for this orbit class a 9 x 9 gravity model is sufficient.Page 46R. Wolf