Multivariable control of flexible spacecraft

This thesis addresses H-infinity mixed sensitivity and LQR (Linear Quadratric Regulator) control system design for a large flexible spacecraft. The spacecraft consists of a rigid central body with two flexible roll-out solar arrays. In this paper, we look at how changes in spacecraft parameters such as mass, width and length of the solar arrays influence the feasibility of obtaining an acceptable control design. In the following case studies. H-infinity mixed sensitivity and LQR controllers are designed and an analysis is presented.; For the nominal case, a control system is created for the spacecraft given its nominal weight along with its nominal length and width. However, the results show that for the nominal case, arriving at an acceptable control design that attenuates worst-case disturbance torques is not achievable.; Then, in Case 1, an analysis is presented where the spacecraft's mass is increased. As a consequence, the arrays become stiffer. This extra stiffness allows for the design of an acceptable control system capable of attenuating the given disturbances.; In Case 2, the width of the array is increased and its length decreased. The final mass for Case 2 is very close to the nominal case. Similar to Case 1, an acceptable control design is found. However, the torque used for this case is lower than in Case 1.; The final results for both cases show that in Case 2, driving the initial states to zero uses less torque than in Case 1. Also, since adding extra weight to the spacecraft is undesirable, Case 2 seems to be the most appropriate solution to the control problem.