Resarch Of The SINS/CNS Based On Star Sensor

With the development of deep space exploration,space craft and lunar exploration,the autonomous navigation has become a crucial technology.At the same time,the development of electromagnetic countermeasure(ECM)exposures some shortcomings of GPS and radio navigation.In this case,strap-down inertial navigation and celestial navigation integrated system(SINS/CNS)becomes an attractive one.In this paper,I in-depth study INS/CNS and the star identification technology based on the high performance carrier such as airplane and ballistic missile.Star identification technology is critical for attitude determination.Therefore,I studied many star identification algorithms,especially the grid algorithm.It is robust against the noise,and has been proved to be an attractive method in the complex noise environment.However,it has a limitation that it needs at least 6 stars in sensor image.This requirement indicates that it is unsuitable for star trackers with narrow FOV or small magnitude limitation.A method named extended images may break this limitation.Its basic idea of the identification algorithm is extended the images with the information output by gyroscope and the data record at previous time step.Inspired by this idea,I modified the grid algorithm.This new algorithm has robustness for position errors and gyro errors related to update time for the star tracker with narrow FOV.This research would enable star trackers practicable to be used in small satellites and perform well in hostile environment.With the widely application of the starlight refraction method,the refraction star identification has become a research direction.In previous studies,two star sensors have been used for refraction star identification.Actually,only one star sensor is sufficient.The additional sensor will result in an extra burden for initial alignment process and design cost.In this paper,a refraction star identification scheme use only one star sensor is presented.The installed angle of star sensor is closely related with the navigation precision.Hence the determination of installed angle is also considered in this scheme,a method to calculate the optimal installed angle is given based on the spherical geometry and differential theory.Star tracker is the most commonly used attitude sensor in celestial navigation.And with the development of microelectronic technology,optical technology and star identification algorithm,the modern star tracker has a high output frequency and good performance in high dynamic environment.Therefore,the application of SINS/CNS in high dynamic environment has been realized.Under high dynamic condition,the traditional SINS/CNS method can not completely separate the rotation and translation,and yield the cone error and rowing error.Tosolve this problem,the dual quaternion is applied to SINS/CNS.The rotation and translation of carrier were unified by this algorithm,and the rotation vector was used to update dual quaternion and compensate coning error and sculling error at the same time.And derived error model based on the additive dual quaternion and error equations of navigation parameters.Then the constant errors of gyro and accelerometer were extended to be state variables,at the same time random error was used as the system input noise,and gyro drift was corrected by output parameters of star sensors.Finally,Kalman filter was used to estimate the state variables.The simulation results showed that the navigation precision of SINS/CNS integrated navigation algorithm based on the additive dual quaternion is significantly higher than traditional algorithm in high dynamic conditions.The positioning accuracy of SINS/CNS integrated navigation system depends on the sensitive accuracy of the earth's horizon.Because of the limitations of level benchmark,the positioning accuracy of the traditional SINS/CNS integrated navigation system is low.At the same time,the traditional method can not accurately estimate the bias of accelerometer,lead to the divergence of the position error and velocity error.To solve the problem,the starlight refraction method is applied to SINS/CNS.According to the previous studies,the observation model of the integrated navigation system is constructed based on the ballistic missile.The output posture of the star sensor corrects gyro drift,and combines with the atmospheric refraction model,the starlight refraction angle can be got which is used to correct the position and velocity error.And in terms of the state-of-the-art of star tracker,I research the possibility that multiple stars used on the SINS/CNS.Finally,the observability and simulation results indicate the feasibility and superiority of this study.