Research On The Orbit Navigation And Control Of The Satellite Cluster

With the rapid development of the aerospace missions, the satellite cluster flight has become an important focus of the aerospace field all over the world. Satellite cluster is described as a kind of satellite system in which multiple satellites remain in close spatial region, satellite communication links are utilized to achieve information exchange and task collaboration. Compared with traditional satellite formation flying technology, satellite cluster has the particularities:1) satellite cluster does not depend on the relative measurement information, all the members remain in a certain region for long time, but does not provide a precise inter-satellite phase and distance contact, and do not maintain a strict configuration;2) the long-term autonomous abilities are needed, such as autonomous navigation, long-term orbit designed and establishment and the strategy for orbit-keeping and collision avoidance and so on. Based on these particularities, this dissertation focuses on the long term autonomous navigation, the establishment of the cluster flight and the strategy of cluster flight safety. The major contents of this dissertation are consisted of the following parts.Firstly, the formulations of the mean orbital elements are derived. The coordinate frames are analyzed, the proper frame for this dissertation is selected. The mathematical description of the osculating orbital elements is presented. The mean orbital elements are defined from the osculating orbital elements. A semi analytical dynamical model of mean orbital elements that includes zonal/tesseral/sectorial harmonics and drag is formulated to capture the daily, long-periodic, and secular evolution of the mean orbital elements.Secondly, a new approach for onboard estimation of mean orbital elements is studied based on recursive filter for long-term autonomous navigation. The filter model of mean orbital elements is formulated. The Extend Kalman Filter (EKF) and Unscented Kalman Filter (UKF) are served as estimator The spherical simplex sigma-point selection and the square root form of UKF are fused for less computational cost and better numerical stability on-board A kind of direct computation method is presented for comparisons The effectiveness and robustness of the filter-based mean orbital elements estimation approach is validated by numerical simulations of three conditions, including without orbit maneuver, with impulsive orbit control and with continuous orbit control. And the accuracy is compared by the simulations.Thirdly, the initial orbit establishment approaches are studied for distance bounded cluster flight. According to the special requirement of cluster flight mission, the distance-bounded natural orbit using mean orbital elements is derived under the perturbation of zonal harmonics and spherical drag. For fuel balance, a kind of distribute orbit controller is offered to establish cluster initial orbit, using cyclic strategy and constant continuous thrusters, and the stability of the orbit control law is proven. The controller is simplified for the near circular orbit mission. For fuel optimal, a kind of Improved Gauss Pseudospectral Method (IGPM) is offered. The nonlinear state integral constraint is transformed into the equivalent linear form for faster convergence speed. The closed-loop control strategy of IGPM is used to decrease the effects of undesired errors and uncertainties. The effectiveness of the initial orbit constraints and two kinds of orbit establishment approaches are validated by numerical simulations.Finally, the cluster flight and collision avoidance strategies are studied to fulfill the safety requirements. A cluster-keeping strategy and cluster-keeping controller is developed for the relative distance of any pair of cluster members reaches the upper or lower bound using the relationships of relative distance, orbital elements and distant-bounded constraints. To ensure the safety, the collision warning level is used to evaluate the collision risk. The collision probability calculation methods are given. The prediction method of the time duration for collision is derived. Two collision avoidance maneuver strategies are given based on collision probability and relative distance, respectively. The thruster working duration constraint is offered. The desired conditions for postmaneuver orbit are designed. The effectiveness of strategies is validated by numerical simulation.