Optical Navigation And Autonomous Control Methods Research For Small Body Probe

As a key technology of small body probes, the level of navigation guidance and control technology determines the function and performance of probes, and impacts on the mission's success. Developing advanced navigation and control methods become research focus in the small body exploration fields to improve the probes' enduring survivability. With the supports of 863 Program'Autonomy Technology of Deep Space Exploration and its Simulation and Demonstration System'and National Natural Science Foundation of China'Theory and Method of Deep Space Autonomous Navigation', this dissertation deeply studies the optical navigation and autonomous control methods of small body probes. The main contents of this dissertation are as follows:Firstly, the approaching orbit determination and autonomous encountering guidance methods are studied. Considering the characteristics of small body exploration and referencing on existing main methods, the navigation scheme and algorithms are designed and analyzed. A predictive guidance law is proposed for small body encountering probes. The maneuver opportunity selecting rule is presented by analyzing the effects of the guidance parameters, such as maneuver timing and aim point, on the intercept performance. In the selecting rule, error ellipse on the B-plane is utilized to describe confidence level of predictive intercept point to improve the basic predictive guidance law.Secondly, the around orbit parameters and small body physical parameters determination methods are studied. Due to a great deal of parameters to estimate and the complexity of the dynamics, a Square Root Information Filter(SRIF) is designed to estimate the gravity field, rotation, and ephemeris of small body and orbit parameters of probe. For the problems arising from evidently uncertainty and strongly nonlinear of orbit dynamics models, an autonomous navigation algorithm based on landmarks using the Gauss-Markov process and Unscented kalman filter is presented, to improve the precision of orbit estimation and ensure the stability of algorithm. The landmark selecting rule is summarized by analyzing the factors affecting the orbit determination accuracy using the singular value and condition number of observation matrix. Next, autonomous descending position and attitude determination and control methods are studied. To reduce the algorithmic complexity and improves solving precision, the position and attitude are decoupled to determine by importing the observation angles between measured line-of-sights. A novel landmark selecting scheme is suggested by analyzing how the landmarks geometry configuration affecting the navigation precision. For impulse maneuver control manner, an autonomous close-loop feedback control method is proposed. Considering the constrain of vertical soft landing, brake maneuvers are planed using artificial potential function guidance method to suppress the dynamic parameter uncertainty and the dynamic disturbances.Then, autonomous landing state estimating and control methods are studied. Considering the requirements of autonomous and real-time for small body landing, based on laser range finder and optical navigation camera to track the target landing point,an autonomous optical navigation algorithm is proposed. With geometry relation of measured vectors and target point, normal direction of the landing plane and the target point position are obtained. In order to achieve vertical landing, the expected descend trajectory characteristic is analyzed, and an impulse guidance and control law based on guidance variable is presented. The high precision soft landing mission is achieved by restricting the angle between line of sight of target point and normal direction of the landing plane.Finally, the navigation and control hardware system and software system are composed by analyzing the system functions and design requirement. The semi-physical simulation system is built up based on dSPACE real-time simulation computer, PC104 computer, optical navigation camera, star tracker, geomorphy simulator and star field simulator. The performance of the navigation and control methods are confirmed by the semi-physical simulation and analysis.