| As the largest number of spacecraft,earth satellites occupy an important position in many fields such as earth observation,weather forecasting,communication and navigation.With the development of aerospace science and technology and the increase of complex space missions,the requirements for the autonomous operation capabilities of earth satellites have gradually increased.Autonomous navigation technology is an important prerequisite to realize the autonomous operation of earth satellites,and it has also attracted widespread attention because of its strong anti-interference and high reliability.Compared with MEO(Medium Earth Orbit)and HEO(High Earth Orbit)satellites,LEO(Low Earth Orbit)satellites have the advantages of high accuracy of earth observation,short communication delay,and low link loss.Combining starlight refraction navigation with inertial navigation can improve the overall accuracy and reliability of the navigation system.Therefore,in order to improve the navigation performance of the LEO satellite,this paper takes the LEO satellite autonomous navigation technology as the research background,and focuses on solving the key technical problems involved in the stellar refraction/INS(Inertial Navigation System)integrated navigation system.Firstly,the model of the stellar refraction/INS integrated navigation system is established.Stellar refraction navigation system can obtain high-precision navigation information by observing the refracted starlight indirectly sensitive to the horizon,while inertial navigation technology,as a classic autonomous navigation technology,complements advantages of the stellar refraction navigation.The integrated navigation system based on both can effectively improve the autonomous navigation performance of the LEO satellite.Secondly,for the inertial navigation misalignment angle and the installation error of the star sensor in the integrated navigation system lead to the degradation of the overall performance,a new system error online calibration strategy is proposed.Because the star sensor cannot make continuous observation of refracted starlight,the observability of the system is weak in some periods,so it is difficult for the traditional filtering method to estimate the system errors of all navigation equipment fast and accurately.In this paper,the rotation information output by the inertial navigation and the star image point information output by the star sensor are used to construct the measurement.The relationship equation between the measurement and the error is established,and solved by the least square method.The results of Monte Carlo target practice simulation show that compared with the traditional filtering estimation method,the online calibration method of the system error proposed in this paper can estimate misalignment angle of INS and the installation error of the star sensor effectively and fast.And after the error online calibration,the navigation performance of the integrated navigation system can also be guaranteed without subsequent filtering state estimation.Then,in order to improve the observability of the starlight refraction navigation system,an optimal design method of stargazing scheme considering stargazing azimuth,quantity,quality and dispersion is proposed.For the different stargazing configurations corresponding to different stargazing directions,the navigation accuracy is also different.A simplified model of refraction apparent height and position error is established for the position and orbit determination problem.By the numerical optimization method,the optimal star-gazing azimuth is determined,and the influence law of star-gazing configuration on position and orbit determination accuracy is obtained.For many other factors that affect the navigation accuracy,the integrated navigation simulation analysis is carried out by controlling the variables one by one,and the influence law is summarized into three dimensions: star-gazing quantity,quality and dispersion.Based on the above research,a general and effective star selection criterion is provided for the observation of refracted stars of LEO satellites.Finally,for LEO satellites that perform typical approaching orbit change navigation tasks,the integrated navigation scheme is designed,the online calibration of the integrated navigation system error is completed,and the refractor star observation plan before and after orbit change is optimized.The integrated navigation simulation is carried out based on the standard orbit data of the satellite generated by STK(Satellite Tool Kit).The simulation results show that the above-mentioned system error online calibration method and the optimized star-gazing scheme are effective,realizing the rapid convergence of the error of the integrated navigation system before and after the orbit change,and ensuring the successful completion of the autonomous navigation task of the LEO satellite orbit changing. |
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