Theory And Software Development On Autonomous Orbit Determination With Spaceborne GPS Measurements

With the development of our country astronautics science and technology, the astronautical mission will increase unceasingly; so the traditional earth-based TT&C are in the high activity, especially the rapid development of small satellite which required the high accuracy parameters of the entire trajectory recently. If the earth-based TT&C will still be used to track these small satellites, not only it will take expensive cost day by day, but also it is much difficult to build the ground stations all over the world. Therefore, the technical development of the high accuracy spacecraft autonomous orbit determination is an imminent task.The developed science and technology such as spaceborne GPS reciver, GPS satellite navigation system and the precise orbit determination theory, has provided the advantageous condition for the high accuracy autonomous navigation. However, the autonomous navigation system will determine satellite real-time trajectory on the processor onborne, so that the autonomous navigation theory is much different from the precise orbit determination. According to the existing orbit determination theory, this dissertation established the high accuracy autonomous algorithm with spaceborne GPS measurements theoretically, and developed spaceborne GPS autonomous navigation software (SATODS) practically. The autonomous navigation experimental results from plenty of data collected from CHAMP and SAC-C missions are presented. The results have demonstrated that the orbit accuracy can achieve±1.5~3.0 meter and velocity accuracy±3 millimeters/second with GPS broadcast ephemeris. Moreover the autonomous navigation software may apply in the period of orbit maneuver. The concrete contents and the main contributions are as follows:On the basis of brief summary of dynamics orbit determination theory, 4 step Runge-Kutta-Fehlberg integrator was used as orbit integration method of autonomous navigation with numerical simulations and the state transition matrix was calculated directly instead of numerical integration method. In view of processor onboard with limited computation ability, serval key problems were researched in order that autonomous navigation will enter into practical application in the future. These problems include that: the optimized recursion algorithm was introduced to reduce computation consumes; the reasonable order of gravitational field model and which of the other perturbation forces were selected and the reasonable step time of integrator was determined with plenty of numerical analysises, 5 step Hermite polynomial interpolation algorithm was introduced to output high density trajectory parameters and so on.Spaceborne GPS measurements are different from that on the ground because of spaceborne GPS receiver move at the speed of several kilometer/second. Therefore each erroneous source and the correction model in the spaceborne GPS measurements were discussed in detail. Ionospheric correction model for single frequency spaceborne GPS users was presented. A valuable accuracy assessment method of pseudorange of spaceborne GPS measurements was reduced. The results computed from data collected from CHAMP and SAC-C missions will contribute to determine the observation noise covariance matrix in autonomous navigation and support the design of optimal data weighting strategies in precise orbit determination applications.Innovation sequence detecting outlier method was presented to delete outlier data of spaceborne GPS pseudorange measurements with orbit parameters predicted. The observation data collected from CHAMP and SAC-C onboard GPS receivers were tested with this method that code outliers amount to 1.2% and 3.0% respectively. The geometry real-time orbit determination will appear on several hundred meter even kilometer trajectory errors if these outlier can not be deleted.The geometry real-time orbit determination with spaceborne GPS measurements was discussed and tested with two days data collected from CHAMP and SAC-C onboard GPS receivers. Serval key problems were summarized according to the results of simulation computation if the spacecraft had used geometry real-time orbit determination as main method of autonomous navigation.Based on theory of Kalman filtering, the integration algorithm of autonomous navigation with spaceborne GPS measurements was presented and deduced. And autonomous navigation software (SATODS) was independently developed with standard C/C++ programming language according to this new algorithm. Many simulation experiments were carried on with observation data from CHAMP and SAC-C missions. The computation results demonstrated that the orbit accuracy could achieve±1.5~3.0 meter and velocity accuracy±3 millimeter/second with this algorithm and software. This accuracy of automous navigation with spaceborne GPS measurements is equal to international ones. Moreover because this algorithm had considered some resons of Kalman filtering divergence, the SATODS software has strong stability, replantability, fast computation speed and so on.In this dissertation, main innovating points of some research contents were summarized as follows: Innovation sequence detecting outlier method was presented to delete outlier data of spaceborne GPS pseudorange measurements with orbit parameters predicted. This method can not only delete code outliers of spaceborne GPS measurements, with other methods in the measurement update of Kalman filtering, but also eliminate the effects of bad GPS broadcast ephemeris and clock error.The integration algorithm of autonomous navigation with spaceborne GPS measurements was presented and deduced. It integrated serval theory such as dynamic orbit determination, dynamic model compensation, extended Kalman filtering, U-D decomposition filtering and spaceborne GPS measurement.Autonomous navigation software with spaceborne GPS measurements was developed successfully. This software has successfully been carried on the simulation computation with plenty of data collected from CHAMP and SAC-C missions.The autonomous navigation theory and software with spaceborne GPS measurements have filled in a blank of spaceborne GPS autonomous navigation in our country. It will be helpful to extend GPS to astronautics application.