Research On LEO Satellite Orbit Determination Based On GNSS

Low Earth Orbit(LEO)satellites has been playing a significant role in the fields such as scientific research,national defense and military affairs.The determination of satellite orbit is the premise of implementing various applications,and higher demands for the precision of satellite orbit determination and real-time autonomy are needed.Aiming at the high dynamic operation characteristics of LEO satellites and the requirements of wartime special tasks.In this paper,research on LEO satellite orbit determination based on spaceborne GNSS has been made.The main contents are as follows:In order to acquire high-quality observed orbit determination data,the raw data are preprocessed including precise orbit determination error source correction and real-time cycle slip detection.In algorithm of error source correction,firstly models for multiple system error source correction are established,and data statistics are used to estimate random errors.Then the overall correction scheme and algorithm are designed.Next,the receiver precise clock-error is solved,and the efficiency of correction model is verified by taking the inter-channel consistency as criterion.In real-time cycle slip detection,the measurements are monitored in real time by jointly using elevation angle detection,MW combination,and ionosphere residuals combination methods.Finally,the real data is used to validate the efficient of algorithm.The result shows that with the increase of error source correction terms,the computation results of receiver clock-error turn out converged,and the cycle slip detection algorithm can detect the same or not same cycle slips on two carriers.Therefore,the proposed error source correction algorithm and real-time cycle slip detection algorithm in this paper are valid and effective.For the demand of general navigation,a pseudorange-based orbit determination method of spaceborne GNSS LEO satellites is proposed.Firstly,the double-frequency pseudo range measurements are used to calculate LEO satellite position coordinates by geometric method,which is used as the measurements of filter.During the iterations,the dynamic error source correction is conducted so as to obtain high-quality measurements.Then the state equations are established based on the satellite force conditions,and the observation equations are derived based on the relationship between state variables and observation variables.Next,the LEO satellite orbit parameters are estimate by using extended Kalman filter.Finally,the real data are used to validate the algorithm.The result shows that pseudorange-based orbit determination algorithm proposed in this paper can achieve real-time and autonomous orbit determination.The precision of tangential,normal,and radial position are 0.61 m,0.43 m,and 1.05 m,respectively.In order to obtain real-time orbit determination results with higher precision,a combined orbit determination method based on clock-error modeling pseudorange and carrier phase is proposed.Firstly,Allan variance method is used to model the GNSS receiver clock-error,and the state equations are established combining with orbital dynamics models.Then,double-frequency measurements are used for real-time cycle slip detection,the measurements excluding gross errors and cycle slips are combined with the initial orbital values and precise ephemeris to perform Gauss-Newton iteration.Position,clockerror,and integer ambiguity of satellite are calculated,which are used as measurements of filter and observation equations is deduced.Next,an extended Kalman filter is used to estimate the optimal state variables.Finally,the real data is used to validate the algorithm.The result shows that the clock model built using Allan variance method is a first-order Gauss-Markov process.The clock-error model contributes to enhancing the radial error precision in orbit determination.For combined orbit determination with clock-error model assisted,its tangential,normal,and radial position precisions are 0.23 m,0.13 m,0.34 m,respectively.The velocity precisions are 0.07cm/s,0.07cm/s,and 0.09cm/s,respectively.Compared to method without clock-error assisted,the former achieves 20.59% increase on radial position precision,and 211.11% increase on velocity precision.For the issue of failure to acquire pseudorange information due to limited use of other countries navigation signals,a carrier phase-based orbit determination method for Spaceborne GNSS LEO satellites is proposed.Under the framework of extended Kalman filter,the influence of integer ambiguity is eliminated by utilizing the difference between epochs to realize real-time and autonomous orbit determination of satellites.The algorithm is verified by the real data.The result shows that the tangential,normal,and radial position precisions are 0.57 m,0.38 m,and 0.33 m.The LEO satellite orbit determination algorithm proposed in this paper covers the properties of real time,autonomy,and high precision.It is expected to become a supplement for the existing autonomous orbit determination technologies.