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Orbit Design and Optimization of Regional Navigation Satellite Constellation

Sharif Ahmadian, Alireza | 2014

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 45333 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Assadian, Nima
  7. Abstract:
  8. In this thesis, optimum set of satellite constellations for regional navigation has been investigated. The cost function is the required multiple coverage for navigation in the Iran region with the lowest possible positioning error. In the satellite navigation systems the GDOP (Geometric Dilution of Precision) is a quantitative measure which is usually used to determine the effect of satellites’ orbits geometry on position error estimation. The lower the GDOP, the more precise the navigation would be. In fact, GDOP relates computed satellite-receiver range error to position estimation error. This thesis has two major parts; modeling and optimization. In the modeling of the problem, geographical coordinates of some receiving spots (sites) in four corners of Iran is considered and accessibility between spots and satellites are modeled. The satellites configuration GDOP for each spot can be computed when at least four satellites are in its sight. The objective of the optimization is to minimize the maximum value of GDOP over the time. However, to have a better convergence in the optimization, a penalty function is included in the cost function for the time intervals in which the four-fold coverage is not met. The genetic algorithm (GA) is selected for optimization of the problem. The GA is a well-known and efficient heuristic approach for optimizing the nonlinear and multi-modal problems with many local minimums. This single objective optimization is implemented for different number of satellites between 4 and 7. The design variables of the problem, including the initial orbital elements such as semi major axis, eccentricity, inclination, etc., have been constrained to minimum and maximum possible values. The other regional satellite navigation configurations have been examined. Finally, the results demonstrated that in most cases the regional navigation constellation orbits tend to GEO and inclined GSO satellite orbits. The results are promising and the maximum GDOP is around 2 in unconstrained cases. However, a minimum of five satellites is needed
  9. Keywords:
  10. Optimization ; Genetic Algorithm ; Satellite Constellation ; Regional Navigation ; Geometric Dilution of Precision (GDOP)

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