Research on Key Technologies of Space Objects Surveillance and Tracking in Space-based Optical Surveillance
|School||National University of Defense Science and Technology|
|Course||Information and Communication Engineering|
|Keywords||Space Object Space-based Optical Surveillance Initial Orbit Determination Tracking Extended Kalman Filter (EKF) Perturbation Two-Line Elements (TLE)|
Space surveillance is one of the main means to acquire the situation information in the space. The capability of the space surveillance is the foundation of the dominance in space and is essential for controlling the space in the future. Space-based optical surveillance has great development potential for its advantages in lower power consuming, higher precision, and easier realizing. Based on the analysis on the characteristics of the space-based optical surveillance, the dissertation focus on how to utilize the solid angles measurements obtained by space-based optical sensor to realizing the passive surveillance and tracking of the space objects. The theories and key technologies are discussed and researched particularly, including the initial orbit determination with space-based optical short arcs, space objects passive tracking methods in space-based optical surveillance, tracking and two-line elements (TLE) fitting methods considering the perturbations. The main contributions of this dissertation are demonstrated as follows:Firstly, the working principle, system characteristics and the observation conditions of the space-based optical surveillance system are analyzed. And then compared with the ground-based optical system on the system parameters and targets coverage. The characteristics of the information processing flow and the corresponding information processing technologies are extracted and analyzed. The mathematical models of the space-based optical surveillance are extracted, including the definition and transformation of the coordinates, the kinetic model of the space object, the observation geometry and the solid angles measurements.To solve the problem of the initial orbit determination (IOD) of the un-cataloged target (UCT), the classical Laplace method is studied firstly, and the ill-condition of the IOD with short arc is analyzed. By analyzing the relativity of the short arc measurements and the characteristic of the coefficient matrix, the dissertation ulteriorly demonstrates that the ill-condition and the error characteristic of the IOD of the short arc measurements especially under the situation of the space-based optical surveillance. The concepts of the attributes and the admissible region are introduced, and then the kinetic states of the space object could be effectively constrained within 2-dimension plane of the slant-range and its ratio, using the measurement information extracted from the short arc. Two kinds of the IOD methods, constrained differential correction method and the triangulation iterative subdivision searching method, are put forward based on the triangulation in the admissible region, which take the selected optimal nodes by the cost function as the best initial conditions. Then the initial orbit of the new space object could be determined using two short arcs. The characteristics of the error and the convergency in Admissible Region are discussed according to the analysis on the simulation results.According to the different requirements for surveillance and tracking missions, the Covariance Analysis Describing Function Technique (CADET) is adopted to analyze the error propagating characteristics of the space object. The classical extended Kalman filter (EKF) is studied, the kinetic equation and the state transformation function are deduced especially for the space-based optical tracking. Aiming at the influence of the truncation error in the first order linearization in EKF, unscented transformation (UT) is introduced in the state prediction in order to get the second order approximation to the nonlinear system. Simultaneously the mixed state space is adopted to enhance the stability of the tracking filter, which performs the state prediction in Cartesian coordinates and filter updating in modified sphere coordinates (MSC) respectively. This method is called mixed state sigma points Kalman filter (SPKF) for space-based optical surveillance. Further more, considering the characteristics of the space-based optical measurements and improvement on filtering convergence, the MSC-SPKF method is put forward which is based on state transformation of the sigma points. The performance on tracking precision and convergency of the methods mentioned above are analyzed with simulation results. The definition of the Cramer-Rao low bound (CRLB) and the system observability degree are introduced, and the instantaneous observability degree is brought forward. The factor which may affect the system observability degree are analyzed with the simulation results, and compared with the ground-based system.Considering the influence of the J2 perturbation based on the two-body tracking filter, the kinetic model and state transformation function are deduced. The new EKF and SPKF tracking filters considering J2 perturbation are put forward,. After analyzing on the two-line elements (TLE) and SGP4 orbit prediction model, the single point fitting and sampling fitting method are studied and modified. For the space objects whose kinetic state is unknown, the new TLE fitting methods are put forward for space-based optical surveillance, which can utilize the bearing-only (BO) measurements to realize the estimation and fitting of the TLE, especially for non-cooperative space objects.