Application of FAMESS to a Large Space Structure Ground Test Facility

Abstract

Filter Accommodated Model Error Sensitivity Suppression (FAMESS) is applied to the problem of regulating the line-of-sight (LOS) of a laser beam pointing system mounted on a 13 meter flexible beam, which is the current configuration of the Marshall Space Flight Center Large Space Structure Ground Test Verification Facility (LSS/GTV). The configuration of the LSS/GTV exhibits many of the pathologies usually associated with large space structures (LSS): (1) low damping, (2) closely spaced modal frequencies, and (3) very low frequency bending modes. Moreover, the sensor/actuator complement of the configuration is not such that colocation of sensors and actuators can be presumed. The collection of techniques commonly known as FAMESS is used to accomplish the design of the LOS regulating control system for the LSS/GTV. These techniques include decentralization, alpha shifting techniques, model error sensitivity suppression, and filter accommodation. Several problems were encountered during the design of the controller for the facility. These problems include computational hardware limitations, proof-mass actuator limitations, controller model sensitivity, constraint placed on the control signals in the sensitivity suppression technique, and problems with modal separation for closely spaced modes. Representative test results are presented and illustrate the dramatic degradation of performance which can be expected when significant system behavior is unmodeled.