Satellite Orbit and Ephemeris Determination using Inter Satellite Links

Inter Satellite LinksOrbit Computation4.3.5 Other PerturbationsOther forces which contribute to the orbit perturbations are• Solid earth tides• Ocean tides• Albedo (reflection from earth)• Third body attraction due to major planetsIn this section, only a few of them will be considered. LEO satellites are subject toperturbations from earth albedo, solid earth tides and ocean loading tides. These perturbationscan be of non negligible magnitude in orbits below 800 km. Here, the major focus is onsatellite orbits suited for navigation applications. A constellation consisting of LEO satellitesrequires a high number of space craft to make sure that always a minimum of four spacevehicles are visible from any location on earth. The required number increases withdecreasing orbit height, thus a navigation constellation would have an orbit altitude above1000 km. Therefore, only two of the minor perturbation are shown in this section.Figure 4-10 and Figure 4-11 show the prediction error due to neglecting solid earth tides. Forthe 800 km LEO, the error is quite noticeable after one day, but for the MEO it is almostnegligible.50Orbit Error [m]-5-10-15-20-25RadialAlong TrackCross Track-30-3506:39:30.000 13:19:30.000 19:59:30.000UTC [hours:minutes:seconds]Figure 4-10 Orbit Error of 800 km LEO neglecting Solid Earth TidesR. Wolf Page 55