Research On Long-term Autonomous Orbit Determination For Navigation Constellation Based On Inter-satellite Orientation Observation

Autonomous orbit determination for navigation constellation is one of the key techniques of au-tonomous navigation which plays an important role in improving the viability of constellation and extending the applications of constellation. Based only on crosslink range observation, which is just able to measure relative positions of satellites in constellation,and can not be able to overcome the barrier of constellation rotation and translation relative to inertial reference frame, the accuracy of autonomous orbit determination is reduced with time.In order to solve this problem, the approach of using inter-satellite orientation observation, that the other satellites in constellation and background stars are observed by star sensor, is put forward to estimate the constellation rotation and translation with the benefit of absolute position information provided by stars. On this basis, a further research on high accuracy and long-term stability of auto-nomous orbit determination for navigation constellation using the information of inter-satellite orien-tation observation is made in this paper.Firstly, model of inter-satellite orientation observation is built. As a result of coefficient matrix of condition equation to precise orbit determination proved to be full-rank, it is available for navigation satellites to realize autonomous orbit determination based only on inter-satellite orientation observa-tion. The results of simulation, which show a good stability but a bad accuracy of autonomous orbit determination using only inter-satellite orientation observation, arise from the technical limitation of the precision of star sensor. While the opposite are true for the results of autonomous orbit determina-tion using only crosslink range observation. Consequently, a combination of two observation methods is designed to make up for each other's deficiencies in the algorithm of autonomous orbit determina-tion for navigation constellation put forward in this paper.Secondly, in view of the fact that most navigation satellites moving in near circular orbits, and also in order to reduce the burden of onboard computer, nonsingular orbit elements are chosen as state vector in this paper when the extended Kalman filter is designed to fuse satellite dynamic model and data of crosslink range observation and inter-satellite orientation observation to determine the orbit. In comparison with position vector and velocity vector chosen as normal, it is available to prolong orbit-al integral step and adopt perturbation resolution expression to calculate the transition matrix, which greatly reduce calculation of onboard computer.Finally, the software for algorithm mentioned above has been developed, and an elementary so- lution for hardware-in-the-loop simulation based on inter-satellite orientation observation has been designed. Simulation experiments, data of which are from IGS (International GNSS services) precise ephemeris of GPS constellation, are performed by means of self-developed software simulation plat-form. The simulation results show that, the proposed algorithm is feasible to maintain both high accu-racy and long-term stability of autonomous orbit determination for navigation constellation. Another interesting conclusion lies in that the requirements can almost be met even if only one group of in-ter-satellite orientation observation left in whole constellation.