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
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<strong>Inter</strong> <strong>Satellite</strong> <strong>Links</strong>AbstractGlobal navigation satellite systems like GPS, GLONASS or the future systems like Galileorequire precise orbit <strong>and</strong> clock estimates in order to provide high positioning performance.Within the frame of this Ph. D. thesis, the theory of orbit determination <strong>and</strong> orbit computationis reviewed <strong>and</strong> a new approach for precise orbit <strong>and</strong> ephemeris determination <strong>using</strong> intersatellitelinks is developed. To investigate the achievable accuracy, models of the variousperturbing forces acting on a satellite have been elaborated <strong>and</strong> coded in a complex softwarepackage, allowing system level performance analysis as well as detailed evaluation of orbitprediction <strong>and</strong> orbit estimation algorithms. Several satellite constellations have beensimulated, involving nearly all classes of orbit altitude <strong>and</strong> 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)<strong>and</strong> allow easy computation of the satellites position at the desired epoch. The broadcastephemeris model of both today existing satellite navigation systems, GPS <strong>and</strong> 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 <strong>and</strong> 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 <strong>and</strong> clock state monitoring areinvestigated <strong>using</strong> 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 <strong>Orbit</strong>al- und Uhrenparameter, um hoheNavigationsgenauigkeit bieten zu können. Im Rahmen dieser Dissertation wurde die Theorieder <strong>Orbit</strong>prädiktion und der <strong>Orbit</strong>bestimmung erörtert und ein neuer Ansatz für die präzisen<strong>Orbit</strong>bestimmung mit Hilfe von <strong>Inter</strong>satelliten-Messungen entwickelt. Um die erreichbareGenauigkeit und Präzision der <strong>Orbit</strong>bestimmung zu untersuchen, wurden mathematischeModelle der zahlreiche <strong>Orbit</strong>störungen erarbeitet und in einem komplexen Software-Paketimplemetiert. Dieses bietet die Möglichkeit für Systemstudien von <strong>Satellite</strong>nnavigations-Systemen beliebiger <strong>Orbit</strong>klassen, sowie zur detaillierten Untersuchung speziellerFragestellungen der <strong>Orbit</strong>prädiktion und -bestimmung. Eine Reihe von Simulationen mitexistierenden sowie fiktiven <strong>Satellite</strong>n-Navigations-Systemen wurden durchgeführt, derenErgebnisse in dieser Arbeit präsentiert werden.Die präzise <strong>Orbit</strong>bestimmung in einem SatNav-System ist kein Selbstzweck, sondern dientlediglich der Bestimmung der Ephemeridenparameter, die - vom <strong>Satellite</strong> gesendet - es demNutzer-Empfänger erlauben, mit Hilfe einfacher Berechnungen die Position des <strong>Satellite</strong>n zuermitteln. Die Ephemeridenformate beider existierender SatNav-Systeme - GPS undR. Wolf Page iii