Application of SISO and MIMO Modal Analysis Techniques on a Membrane Mirror Satellite

Abstract

The future of space satellite technology lies in the development of ultra-large, ultra-lightweight space structures orders of magnitude greater in size than current satellite technology. Such large craft will increase current communication and imaging capabilities from orbit. To get ultra-large structures in space, they will have to be stored within the Space Shuttle cargo bay and then inflated on-orbit. However, the highly flexible and pressurized nature of these ultra-large spacecraft poses several daunting vibration and control problems. Disturbances (i.e. on-orbit maneuvering, guidance and attitude control, and the harsh environment of space) wreck havoc with the on-orbit stability, pointing accuracy, and surface resolution capability of the inflated satellite. However, recent advances in integrated smart material systems promise to provide solutions to these problems. Recent research into the use of Macro-Fiber Composite (MFC®) devices integrated into the dynamic measurement and vibration control of inflated structures has had promising results. These piezoelectric-based devices possess a superior electromechanical coupling coefficient making them superb sensors and actuators in dynamic analysis applications. Initially, research was performed on an inflated torus using single-input, single-output (SISO) testing techniques. Since then, steps have been taken to outline a new, multiple-input, multiple-output (MIMO) testing technique for these ultralarge structures. Based on the matrix formulation and postprocessing techniques recently developed, the current work applies these results to an inflated torus with bonded membrane mirror to extract modal parameters, such as the damped natural frequencies, associated damping, and mode shapes within the frequency bandwidth of interest for these structures (5 – 200 Hz). MIMO modal testing techniques are ideal for large, inflated structure applications. The nature of the structure requires the use of multiple sensors and actuators for worthwhile dynamic analysis and control. Therefore, in the future, the results of this work will form the premise for an autonomous, self-contained system that can both identify the vibratory characteristics of an ultra-large, inflated space craft and apply an appropriate control algorithm to suppress any unwanted vibration—all while on-orbit.