Study On Attitude Coordination Control Of Spacecraft Formation

Due to significant roles in some formation missions such as space-based interferometry and synthetic-aperture imaging, coordinated attitude control of spacecraft formation has been paid considerable attention in recent years. In practical situations, for the sake of the existence of the detrimental factors such as model uncertainties, external disturbances, input saturation and time delays in communication links, it's difficult to get satisfactory coordination control performance. To solve such a problem, the robust attitude coordination control scheme is investigated in this research. The main contents of this dissertation are as follows:The study on the attitude control problem for a single spacecraft, which acts as the basis of the coordinated control of spacecraft formation, is performed. For solving the robust attitude regulation problem for flexible spacecraft, by transforming the original attitude kinemics and controlled dynamics to the standard singular perturbation model, a MRP (Modified Rodrigues Parameters) based nonlinear PID controller which can achieve semi-global stability is designed; With suitable Lyapunov functions, quaternion and MRP based model independent controllers which can yield global convergence in the absence and presence of constant disturbances are derived. Aiming to solve the more general tracking control problem, simple robust Lyapunov-based controllers that only require the attitude and angular velocity measurement are proposed. By using well chosen Lyapunov functions and indispensable proof techniques, the global convergence of the proposed controllers in the presence of model uncertainties and external disturbances is proven.Following the above research, a MRP based coordination controller which is robust to constant disturbances is developed. To overcome its drawback of sensitivity to model uncertainties, suitable parameter estimation variables are incorporated to Lyapunov functions, and quaternion as well as MRP based coordination control laws are derived. These controllers are also robust to constant disturbances and information transmission delays among spacecraft. By virtue of a corollary of Barbalat's Lemma, attractiveness of the proposed controllers for the closed-loop systems is proven. In addition, the application of the quaternion based controller in particular situations and the coordination controller design problem for flexible spacecraft formation are discussed.To further obtain coordination controller which is still globally convergent in the presence of general bounded disturbances, and improve the transient performance in the attitude coordination control, proper coordination variables are chosen and quaternion as well as MRP variable structure control algorithms with clear structures are derived based on Lyapunov's direct method. These controllers are insensitive to model errors, exogenous disturbances and intercommunication delays. For recovering the balance between the absolute motion control and relative motion control, modified versions of the proposed controllers are also presented. Moreover, robust saturated coordinated controllers which possess global convergence are developed, and a MRP based attitude coordination control law for flexible spacecraft formation in the presence of model uncertainties and bounded disturbances is designed.Since the attitude kinematics and dynamics can be transformed to the second order Lagrange equation, the coordination control problem in terms of such a general dynamics is investigated. First, a coordination control law which is globally asymptotically stable in the presence of model uncertainties and disturbances is proposed. Then, its improved versions are presented. Using these results, the control problems of rigid spacecraft attitude coordination and double integrator system coordination are solved. In some particular cases, it can be found that the truncated versions of the controller developed for the general Lagrange dynamics are also applicable.For the controller presented in this dissertation, numerical simulations using Matlab are carried out to validate the theoretical results. In addition, the animation demonstration using STK are performed to test the control results of spacecraft formation for beam synchronization.