Satellite Orbit and Ephemeris Determination using Inter Satellite Links
Satellite Orbit and Ephemeris Determination using Inter Satellite Links Satellite Orbit and Ephemeris Determination using Inter Satellite Links
Inter Satellite LinksPage iiR. Wolf
Inter Satellite LinksAbstractGlobal navigation satellite systems like GPS, GLONASS or the future systems like Galileorequire precise orbit and clock estimates in order to provide high positioning performance.Within the frame of this Ph. D. thesis, the theory of orbit determination and orbit computationis reviewed and a new approach for precise orbit and ephemeris determination using intersatellitelinks is developed. To investigate the achievable accuracy, models of the variousperturbing forces acting on a satellite have been elaborated and coded in a complex softwarepackage, allowing system level performance analysis as well as detailed evaluation of orbitprediction and orbit estimation algorithms. Several satellite constellations have beensimulated, involving nearly all classes of orbit altitude and the results are compared.The purpose of orbit determination in a satellite navigation system is the derivation ofephemeris parameters which can be broadcast to the user community (or the other satellites)and allow easy computation of the satellites position at the desired epoch. The broadcastephemeris model of both today existing satellite navigation systems, GPS and GLONASS areinvestigated, as well as two new models developed within this thesis, which are derivates ofthe GLONASS model.Furthermore, the topic of autonomous onboard processing is addressed. A conceptual designfor an onboard orbit estimator is proposed and investigated with respect to the computationalload. The algorithms have been implemented. The main benefits of ISL onboard processing,especially with respect to the great potential to ephemeris and clock state monitoring areinvestigated using complex simulations of failure scenarios. By simulating several types ofnon-integrity cases, it is showed that one single fault detection mechanism is likely to beinsufficient. Within the algorithm design of the onboard processor, a reasonable combinationof fault detection mechanisms is presented, covering different fault cases.ZusammenfassungGlobale Navigationssysteme wie GPS, GLONASS oder zukünftige Systeme wie Galileoerfordern die hochpräzise Bestimmung der Orbital- und Uhrenparameter, um hoheNavigationsgenauigkeit bieten zu können. Im Rahmen dieser Dissertation wurde die Theorieder Orbitprädiktion und der Orbitbestimmung erörtert und ein neuer Ansatz für die präzisenOrbitbestimmung mit Hilfe von Intersatelliten-Messungen entwickelt. Um die erreichbareGenauigkeit und Präzision der Orbitbestimmung zu untersuchen, wurden mathematischeModelle der zahlreiche Orbitstörungen erarbeitet und in einem komplexen Software-Paketimplemetiert. Dieses bietet die Möglichkeit für Systemstudien von Satellitennavigations-Systemen beliebiger Orbitklassen, sowie zur detaillierten Untersuchung speziellerFragestellungen der Orbitprädiktion und -bestimmung. Eine Reihe von Simulationen mitexistierenden sowie fiktiven Satelliten-Navigations-Systemen wurden durchgeführt, derenErgebnisse in dieser Arbeit präsentiert werden.Die präzise Orbitbestimmung in einem SatNav-System ist kein Selbstzweck, sondern dientlediglich der Bestimmung der Ephemeridenparameter, die - vom Satellite gesendet - es demNutzer-Empfänger erlauben, mit Hilfe einfacher Berechnungen die Position des Satelliten zuermitteln. Die Ephemeridenformate beider existierender SatNav-Systeme - GPS undR. Wolf Page iii
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<strong>Inter</strong> <strong>Satellite</strong> <strong>Links</strong>Page iiR. Wolf
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