Satellite Orbit and Ephemeris Determination using Inter Satellite Links

Autonomous Onboard ProcessingInter Satellite Linksclock parameters would be updated at a higher rate than 24 hours, say every 6 hours, toprevent excessive positioning service degradation. This would keep the position error below 2meters.7.4.2 User Position Degradation due to Unforeseen Orbit ManoeuvreBut not only the normal orbit degradation impacts the user position. If something happenedwith the satellite clock, say an excessive increase in frequency (clock drift), this could not beovercome by frequent parameter updates. Especially if the integrity requirement an thesatellite position and clock is high, as would be the case in airborne navigation, the user cannot rely on predicted orbits only. In the following simulation, one 2 Newton thruster of theorbit control system of SV 26 is fired, resulting in a small 0.1 m/s velocity increment. At thetime the event takes place, the satellite is in view of the user position.Radial Error [m] 1998 07 01 12:01 - 1998 07 01 12:2950.025.00-25.0-50.0[min]5 10 15 20 25Along Track Error [m] 1998 07 01 12:01 - 1998 07 01 12:2910.05.0-5.00-10.0[min]5 10 15 20 25Cross Track Error [m] 1998 07 01 12:01 - 1998 07 01 12:2952.026.0-26.00-52.0[min]5 10 15 20 25Clock Error [m] 1998 07 01 12:01 - 1998 07 01 12:280.00.0-0.00-0.0[min]5 10 15 20 25Figure 7-8 SV 26 Orbit Error due to 2N Thrust / 0.1 m/s Delta VPage 172R. Wolf