Concurrent fuzzy logic control of a gimballed payload and space platform system

A fuzzy logic control methodology is developed in this dissertation to enhance attitude control and instrument/payload pointing on a class of spacecraft that consists of rigid structures with flexible appendages and multiple scanning/tracking science instruments and subsystems. The methodology is applicable for using fuzzy logic control on two systems which are dynamically coupled but with separate mission objectives.; First, a dynamic model of a space platform with multiple payloads is developed. Payload-payload and structure-payload disturbance-response transfer functions are derived from the model. The Euler beam equation with the appropriate boundary conditions is developed to analyze the short-term (orbital) periodic changes in modal characteristics when flexible appendages such as solar array rotate and the long-term effects due to mass expenditure (fuel and/or cryogen expenditures). As the appendage transverse vibration varies from about the roll axis (minimum tip inertia) to the yaw axis (maximum tip inertia) on the spacecraft, the modal frequencies, mode shapes and resulting spacecraft vibration amplitude vary as a consequence of the rotation. Due to the changing orientation of the appendage mode shapes with respect to the fixed disturbances on the spacecraft, the disturbance transmission to the mode shapes and the resulting vibration response also varies with rotation of the appendage. Because the spacecraft's latitude varies with solar array rotation, the resulting vibration response is latitude specific.; Second, fuzzy logic control is applied to the payload/platform system. The fuzzy controllers outperformed controllers designed using Linear Quadratic Regulator (LQR) control design. An optimization approach is used to tune membership functions for all linguistic variables to achieve global performance. The approach allows design constraints to be implemented during the tuning process. The optimization approach provides a simple and direct means to tune fuzzy controllers. The platform feedback control is augmented with fuzzy feed-forward control (using input from the payload controller) to reduce the platform attitude error resulting from deterministic payload disturbances. The platform feed-forward controller is tuned using the optimization approach with the response as a performance index (objective function). The augmented feed-forward control significantly reduced the platform response to the payload disturbance.