Attitude Control And Trajectory Optimization Of Solar Sail Spacecraft

With the rapid progress in the aerospace field, the human have left their footprints in a vast space from their homes on the earth. As a class of novel space technology, solar sail offers a broad prospect for human to achieve in-depth exploration of the solar system and even interplanetary flight. Solar sail is a thruster propelled by means of a continuous sunlight pressure, which can provide a continuous low-thrust for the spacecraft. It does not need to carry large amounts of fuel, and can be used to fight on the orbit of some non-traditional tasks, such as imaging and real-time communication of high-latitude regions of the earth, detection of terrestrial planets, sample return mission and so on. Therefore, solar sail technology has broad application prospects for deep space exploration and interplanetary flight, and has been concerned widely by the international aerospace community in recent years.The features of solar sail spacecraft include the intense coupling and nonlinear relationship between the attitude dynamics and its flexible structure such as the large-scale film sail and booms. Namely attitude adjustment will induce flexible structural vibration, thereby affect the spacecraft's thrust magnitude and direction. Furthermore, compared with conventional spacecraft, solar sail spacecraft needs a relatively long period for transferring to the target orbit, thus it is necessary to optimize the transfer trajectory of solar sail spacecraft between the initial orbit and the target orbit. Consequently, researches on attitude dynamics modeling and control of solar sail spacecraft, and its transfer trajectory optimization have important practical significance and an extremely high theoretical value.This paper is mainly focused on attitude dynamics modeling and control of solar sail spacecraft, and its orbit transfer optimization problem. Based on the current typical configuration of solar sail and its rigid dynamics model, combined with the relevant research of rigid-flexible coupling dynamics, the linear and nonlinear attitude dynamics model of solar sail spacecraft and the corresponding attitude control method were studied respectively. For solar sail spacecraft trajectory optimization problems, in the light of the latest researches on he evolutionary algorithm and the multi-objective methods, the optimal transfer trajectory of the solar sail spacecraft for different tasks are studied.Existing literature shows that the pitch-axis rigid body dynamic model of solar sail spacecraft can not accurately describe the characteristics of its flexible structures. In Chapter Two, dynamic responses of solar sail spacecraft rigid body model controlled by the gimbal system and reaction jet were analyzed respectively. Based on the rigid body dynamics, combined with the idea of the hybrid coordinate method, solar sail spacecraft attitude dynamics model with the rigid-flexible coupling characteristics was established. In order to suppress the vibration of flexible structures induced by the attitude adjustment process of solar sail spacecraft, and ensure its accuracy and stability of the attitude adjustment, the Hoo controller was designed for the rigid-flexible coupling dynamics model of solar sail spacecraft. The goal of control is to achieve the asymptotic tracking of the target attitude angle, and robust vibration suppression of flexible structures.Small angle approximation of solar sail spacecraft dynamics model can not accurately describe its dynamics. In Chapter Three, the pitch-axis nonlinear rigid body dynamics model controlled by the gimbal torque and reaction jet force was established firstly. Then through the hybrid coordinate method, solar sail spacecraft nonlinear rigid-flexible coupling attitude dynamics model was derived. Based on the model, a local small-angle approximation was performed on the attitude angular change rate, gimbal angel and its change rate, and the model was transformed into the form of matrix second-order system. And under some assumptions, solar sail spacecraft rigid-flexible coupling nonlinear attitude dynamics model was translated into a class of polytopic linear parameter varying (LPV) system. And then the linear state feedback control law was designed for the system, and the solution of the control law parameters was obtained by solving the convex optimization problem with linear matrix inequality (LMI) constraints. Finally the simulation example of solar sail spacecraft attitude angle tracking demonstrates the effectiveness of the method.The fuel carried by the solar sail spacecraft is limited, and its attitude adjustment has the characteristics of a long period and small magnitudes. Considering those features, based on idea of the direct shooting method, the piecewise linear interpolation method was used in Chapter Four for approximation of continuous-time changes of attitude angle. And then combined with the mechanical model and the features of solar sail trajectory optimization, solar sail orbit transfer optimal control problem was turned into parameter optimization problem. Then differential evolution algorithm and the improved imperialist competitive algorithm were used respectively to achieve the transfer trajectory optimization of solar sail spacecraft for a variety of tasks, and the optimization results are comparative analyzed.The solar sail spacecraft trajectory optimization was characterized by the inherent constraints on the parameters to be optimised, and the multi-objective optimization theory can be used to deal with such problems. In Chapter Five, a Nondominated Sorting Big Bang-Big Crunch (NSBBBC) method was proposed, through the proposed threshold selection strategy and elitists'preservation scheme, as well as a constraint handling approach without penalty parameters, the solar sail spacecraft trajectory optimization problems were classified and studied. Finally, the feasibility of the approach was verified by numerical examples.