Research On Integration Of Autonomous Orbit Determination And Orbit Maintenance Control Of Navigation Constellation

The safety of navigation satellites is of great significance to the economy,people’s livelihood and national defense.Navigation satellites are the principal part of the navigation function,but at the same time,they also rely on the coordinated work of ground stations to control the satellites and maintain their orbits.Once the ground station is attacked or interfered,the normal functions of the navigation satellites will be affected or even completely lost.And with the rapid increase in the number of navigation constellation satellites,the measurement and control burden and pressure faced by ground stations will also increase,which will have to consume greater manpower and material costs.The autonomous navigation technology based on the inter-satellite ranging can reduce the dependence of the earth navigation constellation on the ground station,which not only reduces the working pressure of the ground station,but also maintains precise of orbit determination for a period of time under extreme conditions(when communication with the ground station cannot be obtained).The accuracy of autonomous orbit determination enhances the independent survivability of the navigation constellation and improves its safety under special conditions.In order to solve the problem that the global rotation constellation cannot be eliminated when relying solely on intersatellite ranging to achieve autonomous orbit determination,the introduction of a Lagrange navigation constellation to form an extended navigation constellation is a better solution,which can not only realize the truly autonomous operation of the space-based satellite navigation system,but also extend the service area of the navigation constellation to deep space exploration.However,existing studies on extended navigation constellations have not considered orbital maneuvers.In fact,orbit maintenance often accompanies the entire life cycle of navigation satellites.To make navigation constellations truly long-term autonomous operation capabilities,it is necessary to consider both autonomous orbit determination and autonomous orbit control.Considering that the dynamic equations of satellite orbits will change significantly after adding orbit control force,and become a typical nonlinear system,the observability may change.This paper first analyzes the effect of orbit control force on the observability of the system.The symmetry of the coordinates of the dynamic equations and the distribution of the gravitational field draw the conclusion that the observability is unchanged,which lays the foundation for subsequent research.As a member of extended navigation constellation,GEO satellite orbit has some particularity,and the frequency of orbit keeping control is high.In this paper,a dual neural network integrated observation and control scheme is studied for GEO satellite.The neural network is used to improve the modeling accuracy and control accuracy.Through numerical simulation,it is proved that this scheme has better effect than the traditional nonlinear filter.In addition,the joint autonomous orbit determination of extended navigation constellation considering the orbit maneuver of Lagrange navigation satellite is studied.The scheme of autonomous orbit determination based on Unscented Kalman filter and the scheme of autonomous orbit maintain with small thrust control based on joint autonomous orbit determination result are studied.Numerical simulation results show that autonomous orbit determination and autonomous orbit maintain control do not interfere with each other,and the extended navigation constellation can realize autonomous operation.