Flexible Spacecraft Modelling and Control with a Robotic Manipulator

The growing of space debris orbiting around the Earth has become a significant problem for active spacecraft and future missions, due to the risk of collision and the accumulation of artificial objects, especially in Low Earth Orbit (LEO). In order to mitigate the problem, new solutions have been proposed. Space robotics has been included in on-orbit services to help human activities in the space environment, and in particular robotic manipulators can play a key role in active debris removal. The purpose of this thesis is the development of a flexible spacecraft dynamics and control model including a space manipulator. A hybrid approach is used for implementing the main body and the manipulator dynamics. In particular, the manipulator equations of motion are obtained from Lagrangian formulation, while the main body dynamics is expressed with Euler equations for a rigid body. The robotic arm is a two Degrees Of Freedom (DOF) planar manipulator with two links. The main structural properties are chosen after a comparison of space robotic arms from literature. On the other hand, the JAXA micro-satellite PRoximate Object Close flYby with Optical Navigation (PROCYON) is used as the main body of the spacecraft. As in PROCYON spacecraft, a system of four reaction wheels in pyramidal configuration is considered. All modelling and simulation phases are made in MATLAB/SIMULINK environment. Another important aspect of this work is the flexible part of the satellite, represented by the four solar panels of PROCYON spacecraft. A Finite Element Method (FEM) analysis with PATRAN/NASTRAN is conducted to obtain the natural modes and frequencies necessary for the model and a coupling matrix between rigid and flexible parts is also evaluated. The second part of the thesis is about control strategies. Two different controllers are used for the movement of the manipulator and the main body attitude control. A simple Proportional-Integral-Derivative (PID) controller is implemented for the robotic arm, with the purpose of achieving the desired joint angle position for debris/target capture. For attitude control, an Active Disturbance Rejection Control (ADRC) with a Linear Quadratic Regulator (LQR) as control law is used, in order to obtain a fast and stable response with the rejection of all internal and external disturbances acting on the system. The satisfactory results in the simulation environment demonstrate the capability of the ADRC to perform attitude control, although the high disturbance due to the manipulator movement and the vibrations of the solar panels. The PID itself ensures good performance and allows to obtain a stable response of the manipulator.