Research On Centralized Autonomous Orbit Determination Key Technology With Beidou-3 Inter-Satellite Link Ranging

Inter-Satellite Link(ISL)has the capacity for inter-satellite measurement and communication and it is an important part of modern global satellite navigation systems.With the support of ISL,satellite navigation systems can have the ability to achieve Autonomous orbit determination(AOD)which enable satellites to update their ephemeris on-orbit without the support of the Operational Control Segment(OCS),which enhances the vitality of the navigation system in special periods.As one of the fastest-growing satellite navigation system,the Beidou satellite navigation system(BDS)completed an demonstration constellation from March 2015 to February 2016 to verify ISL technology and its application in AOD.Since the first BDS-3 satellite launched in November 2017,up to the end of 2018 the BDS-3 has formed a basic constellation composed by 18MEO+1GEO.All satellites of BDS-3 have equipped with ISL payloads,which realizes inter-satellite measurement and communication based on Ka-band.It is a key issue in the construction of BDS how to realize the autonomous orbit determination with ISL.At present,the United States of America(USA)has a complete theory on GPS autonomous orbit determination,and has achieved AOD on GPS BLOCK IIR and later satellites.However,the key technologies of GPS's AOD system have not been disclosed.In the last fewer years,some domestic scholars have carried out some useful research and exploration on AOD with the simulation data.But the results of applying the ISL to AOD are still relatively few.This thesis aims to systematically study the key technologies in centralized AOD,and apply the BDS-3 ISL to AOD,which is expected to provide a theoretical reference and technical support for the follow-up of China BDS to achieve AOD.The main work and contributions are as follows:(1)The development of satellite inter-satellite links and the research status of AOD are reviewed.Then,the basic theory of satellite orbit determination is summarized,and the mathematical model of centralized AOD based on ISL is deduced in detail.(2)In the Kalman filtering algorithm,the calculation of the gain matrix requires an inversion operation.When the matrix of the inversion in the calculation process loses non-negative characterization,the gain matrix will generate a large error,which will cause a huge error in the parameter estimation.Aimed at this problem and the processing characteristics and requirements of AOD,this paper introduces a Kalman filtering algorithm based on UD decomposition to avoid the matrix inversion operation,which can not only reduce the calculation amount of filter measurement update,but also improve the stability of AOD process.(3)In the conventional batch processing algorithm,the formation of the law equation needs a large amount of computation and the ill-posed problem of the equation may occur.In this paper,a square root free givens transformation algorithm named Givens-Gentleman(GG)is introduced.The significant advantages of this algorithm are that the processing of the observation data is processed one by one,and the large coefficient matrix are avoided to economize memory occupation.Meanwhile,the characteristic of the coefficient matrix in AOD containing a large number of zero elements is used to reduce the calculation amount.The GG transformation algorithm avoids a large number of square root operations,which will improve the efficiency of parameter solving and obtain a higher precision solution.(4)A simple method for the calibration of ISL systematic delay with post and accurate satellite orbits and clock is presented.The results show that the sum of ISL transmission and reception delay has a good stability and the standard deviation(STD)is better than 0.1m within 30 days.However,the stability of the subtraction of ISL transmission and reception is worse than their sum,and the standard deviation(STD)reaches 0.3m within 30 days.(5)A centralized AOD based on filtering processing for 30 days is realized using BDS-3 ISL.The results show that in the case of 18 MEO satellites,the average three-dimensional(3D)error of AOD is less than 2.0m,and the accuracy of the orbital URE is better than 0.5m.The RMS of all satellites' ISL observations post-residuals is less than 0.5m.When checked with SLR,the RMS of the 30-day residual is less than 0.4 m.(6)A batch processing algorithm for centralized AOD is realized.When processing of the BDS-3 ISL,an average radial error less than 0.1m is achieved and the average orbital URE is better than 0.25 m within 7 days.Compared with the filter-based centralized AOD,the radial,tangential and normal accuracy of the orbit can be increased by 11.87%,15.52% and 28.31% in 7 days.