Research On Attitude And Orbit Integrated Dynamics Modeling And Control Technologies For Spacecraft Relative Motion

Several new space missions, such as spacecraft rendezvous and docking, spacecraft formation flying and on-orbit servicing, bring new requirements on spacecraft dynamics modeling and control. In this dissertation, with the background of modeling and control for six-degree-of-freedom(6 DOF) spacecraft relative motion, dual quaternion and screw are adopted as the mathematical tools to systematically research into the problem of the attitude and orbit integrated dynamics modeling, integrated optimal control, integrated control with input saturation constraint, and integrated control of underactuated spacecraft. Furthermore, a hardware-in-the-loop(HITL) simulation system is constructed based on a single-axis air bearing table, on which the proposed control laws in the paper are validated in term of physical validation. The main achievements of this dissertation are as follows.1. The problem of attitude and orbit integrated dynamics modeling for spacecraft relative motion is investigated. The fundamental properties of dual number and dual vector are introduced, followed by the derivation of the concepts of dual quaternion and screw. Then, the equations of relative attitude motion and relative orbit motion are presented based on dual quaternion and screw. Finally, the characteristic of the attitude and orbit coupling of 6 DOF relative motion is analyzed theoretically and demonstrated in detail with simulation cases.2. The problem of integrated optimal control of attitude and orbit for spacecraft relative motion is studied. The severe nonlinear and coupling system model is divided into nominal part and disturbed part. For the nominal part, Lyapunov optimizing control(LOC) technique and the method of Control Lyapunov function(CLF) are utilized to obtain the sub-optimal results of the system, avoiding the trouble of solving the Hanmilton-Jacobian-Bellman(HJB) partial differential equation(PDE) consequently. However, the control accuracy of the result is low. In order to address the problem, the former two methods are combined with integral sliding mode control to design two optimized sliding mode controllers, which can improve the control accuracy of the closed-loop system evidently, and are robust to model uncertainties and external disturbances.3. The problem of integrated control of attitude and orbit for spacecraft relative motion with input saturation constraint is investigated. To solve the problem, three different types of controllers are proposed, respectively. First, Anti-windup control, intelligent integrator and conventional proportional-integral-differential(PID) feedback control are combined to design a new anti-saturation feedback controller, which is simple in configuration and easy for implementation. However, the proposed controller can only reduce the time when the input is saturated, and cannot entirely avoid the case of input saturation. Second, a robust adaptive controller, which explicitly restrains saturation and is fast convergent and robust to model uncertainties and bounded external disturbances, is designed with input saturation constraint. Third, an adaptive variable structure control scheme is presented, which has the following properties: 1) explicit accounting for the problem of input constraint. 2) no chattering phenomenon is present in the control torque and control force. 3) the upper bounds of unknown variables are estimated dynamically. 4) the convergence rate is faster than the second controller.4. The problem of integrated control of attitude and orbit for underactuated spacecraft relative motion is studied. The control object is defined, and the underactuated control problem without input saturation and the one with input saturation considered are analyzed, respectively. In the former analysis, for the relative attitude motion control, the asymptotical stability of the underactuated subsystem for the relative attitude motion is achieved firstly. Then, a generalized sliding mode controller based on generalized inverse and null-control vector is designed to control the other two axes. For the relative orbit motion control, a power optimal trajectory is obtained by the Gauss Pseudospectral method and nonlinear programming. Then, an adaptive sliding mode controller is presented to track the optimal trajectory. According to the former analysis, the latter one combines input saturation constraint with underactuated control and optimal control, then designs a generalized adaptive sliding mode controller to stabilize the relative attitude motion and realize the optimal control of the relative orbit. The second method can weaken the surge trend enormously, obtain faster convergence rate, and consume less power.5. HITL simulation of integrated control of attitude and orbit for spacecraft relative motion is performed. First, a HITL simulation system based on a single-axis air bearing table is briefly introduced, which is used to simulate the pitch channel of the attitude motion. For the control of the other two channels and the relative orbit, however, the simulation is conducted mathematically. Second, HITL simulation is carried out to verify the proposed three different controllers(integral sliding mode control based on CLF, adaptive variable structure control with input saturation, underactuated control of 6 DOF relative motion with input saturation), respectively. Finally, the HITL simulation results are compared with the mathematical ones, demonstrating that the proposed controllers are effective and feasible.