Satellite Orbit and Ephemeris Determination using Inter Satellite Links

Autonomous Onboard ProcessingInter Satellite Links7.4.3 User Position Error with Onboard Integrity MonitoringThe next four simulations have been conducted using the onboard integrity monitor describedabove. This means, there are 33 Kalman filters running in parallel an processing onlymeasurements and information available at the satellite, and at a time when they becomeavailable. It is assumed that the satellites broadcasts its integrity status via inter satellite linkto the other satellites, which then becomes available at the other satellites in the next epoch, aswell as to the user. If a user receives an "Unhealthy" flag from a satellite, this SV is excludedfrom the position solution. The same applies to the satellites monitoring their own status usingISL's. A received unhealthy flag leads to exclusion of this particular link.In the simulation, a non integrity case is assumed, if the position error or the clock errorexceeds 1 meter in each direction. The trigger values for the state vector alarm are therefore:X, Y and Z EstimatedPosition ErrorState Trigger Value Result1 Meter NO GO (Unheathy flag israised)Clock Offset 1 Meter NO GOVX,VY,VZ EstimatedVelocity Error2 cm/s Warning OnlyClock Drift 2 cm/s Warning OnlyFigure 7-11 Trigger Values for Fault Detector7.4.3.1 Strong Orbit ManoeuvreThe first simulated non-integrity case is an orbit manoeuvre with 50 Newtons thrust,producing a velocity increment of 0.5 m/s in the along track direction. The affected satellite isagain SV 26, which is visible to the user at a medium elevation. The resulting orbit error overtime is depicted in the figure below.Page 174R. Wolf