Satellite Orbit and Ephemeris Determination using Inter Satellite Links

Simulations and ResultsInter Satellite Links0.140.120.10URE [m]0.080.060.040.020.002450998.0 2450998.2 2450998.4 2450998.6 2450998.8Julian Date [Days]Figure 6-47 URE without smoothing using ISL'sAlthough the raw estimate has not been smoothed, the orbit prediction error is relativly smallif compared to the propagation of the raw estimate derived from ground based only tracking.A better prediction accuracy can only be achieved if the determined orbit is smoothed over asufficient long period (approximately one orbit revolution).This fact bears an interesting option if fast generation of broadcast ephemeris together with areduced computation load is desired, which is especially interesting for board autonomousephemeris generation.Of course, if highest precision is desired, the ISL aided orbit determination can be smoothedto. The last two figures show propagation error and broadcast ephemris degradation if the rawestimate is smoothed over 12 hours prior to propagation.Note that although the values seems to be slightly better than in the example for the groundbased only derived orbit with 12 hour smoothing, there is in fact no relevant difference in theorbit accuracy. If the orbit is smoothed a sufficient time prior to propagation, it makes nodifference if the raw estimate has been of high or medium accuracy.Page 146R. Wolf