Precise Orbit Determination of Global Navigation Satellite System of ...

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Chapter 1 Introduction 1.2 Development Phase GNSS-2/Galileo system will be developed in the period from 2000 to 2008, building on the experience acquired from GNSS-1. The time schedule for the different steps can be summarized as follows: (Commission Communication to the European Parliament and the Council on Galileo, 2000) Development and Validation Phase 2001 to 2005 Deployment Phase 2006 to 2007 Start of Operation 2008 1.3 Orbit Determination of GNSS-2/Galileo In the early study phase, the typical space segment of GNSS-2/Galileo system was composed of inclined geosynchronous (IGSO), geostationary (GEO) and medium earth orbit (MEO) satellites. Now the space segment of Galileo system is composed of 30 MEO satellites or MEO + GEO satellites. According to the document of EU Commission Communication to the European Parliament and the Council on Galileo 2000, the advantage of the system using such satellites is more uniform in performance both in terms of accuracy and availability and greater robustness in crippled mode. With this new satellite navigation system under control of civilian institutions, the precise navigation and positioning with accuracy of at least 10 meters without differential techniques may be achieved. Therefore high precision orbit determination is required for successful applications of GNSS-2/Galileo system with this accuracy level. There are some new problems for orbit determination of GNSS-2 satellites. For example, due to high altitude of IGSO and GEO satellites, the geometrical distribution of tracking stations will have a greater influence on the accuracy of orbit determination than any other earth satellites, the distances between the satellites and tracking stations will change slowly as satellites move, which leads to some problems in the solution of observation equation, because there are no big differences for observations measured in several minutes. In other words, more observations in a short time will not contribute to improve the accuracy of orbit determination, and when using Doppler-based methods it also does not enhance the accuracy of orbit determination because the Doppler effect will not be significantly sensitive to slow changing of the range rate. Until now the actual accuracy of geostationary orbit determination is in kilometers. The precise orbit determination of a GNSS-2 satellite with comparable accuracy to a GPS satellite, therefore, is a great challenge. In order to achieve highly accurate orbit determination of GNSS-2 satellites, the satellite tracking station distribution and related data processing methods should be carefully chosen to satisfy the accuracy requirement of GNSS-2 system. The tracking systems of orbit determination can be classified as two major types: ground-based tracking systems such as S-Band and Satellite Laser Ranging (SLR) and space-borne tracking systems, for examples, DORIS and PRARE. There are two major kinds of observations for orbit determination: optical and radio microwaves. Basic optical observations are directions and angles. The microwave observation may consist of ranges, range rates (Doppler), and carrier phases. In the dissertation, the current systems of orbit determination using ranges, range rates (Doppler) and carrier phases will be discussed and evaluated. The focus is on ground orbit determination methods. In Chapter 2, the basic observations of orbit determination are discussed; in Chapter 3 current systems used for various orbit determination applications are evaluated; in Chapter 4 major sources of observation errors are analyzed; in Chapter 5 perturbations on IGSO, GEO and MEO are modeled and estimated; in Chapter 6 major algorithms of orbit determination of IGSO, GEO and MEO, for examples, dynamic, reduced dynamic and kinematic methods are developed and discussed; in Chapter 7 high accuracy of IGSO and GEO orbit determination using carrier phase observation are discussed; in Chapter 8 a serious problem of GEO orbit determination during satellite maneuvers is presented and solved, and finally the simulation results of a possible satellite tracking system of GNSS-2 are presented in Chapter 9. IGSO, GEO and MEO satellites are all possible candidates for a GNSS-2/Galileo system. MEO satellites are actually the same type as GPS/GLONASS satellites, therefore in the dissertation, my focus is on IGSO and GEO satellites, i.e. precise orbit determination of IGSO and GEO satellites, including special situation during GEO satellite maneuvers. 2
Chapter 2 Observations of Orbit Determination CHAPTER 2 OBSERVATIONS OF ORBIT DETERMINATION The basic observations of orbit determination are ranges, range rates (Doppler), carrier-phases, laser ranging, etc. According to the applications, these observations may be used for one-way or two-way systems. In this chapter, the basic observations of orbit determination, the possible error budgets, the error models related to the receivers and the advantages and disadvantages based on current satellite navigation systems, GPS/GLONASS are discussed. 2.1 One-Way System In a one-way system the signal transmitted from satellite is received by the ground tracking stations or the signal transmitted from ground tracking stations is received by satellites. The received signal is then processed for orbit determination. In a typical one-way system, the measurement is done by comparing a clock time at the transmitter antenna with a clock time at the receiver antenna. The travel time of the signal is scaled into a range measurement using signal propagation velocity. All microwave observations mentioned above can be used in a one-way system. 2.1.1 Range 2.1.1.1 Basic Observation S(t 2 ) S 1 Figure 2-1 One-way Range Measurement 3 r(t 1 ) S(t 1 ) As shown in Figure 2-1, assuming a clock time at the receiver antenna is t 2 , and a clock time at the transmitting antenna is t1 , the one-way range measurement S1 can be expressed by L = S1 = c( t2 − t1) + ε (2-1) where S1 the geometrical distance between the satellite and ground tracking station c speed of light in vacuum ε measurement noises such as ionospheric and tropospheric errors, multipath effect satellite and receiver errors, and random noises ( t1) r satellite geocenter position vector at t 1
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Chapter 5 Perturbation Models of IG
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Chapter 6 Algorithms of Orbit Deter
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Chapter 7 Orbit Determination Using
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Chapter 8 Geostationary Orbit Deter
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Chapter 9 Software and Simulation R
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Conclusion 144
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References Carpino M. (1995): SAEG
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References Klobuchar, J. A.(1996):
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References Traquilla, J. M. and J.
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Acknowledgments 152
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