Application of Multiple Model Control to Space Structure Systems with Nonlinear Inertia Properties by Kazumi Masuda

Future space systems will require high robustness of the control system as well as high performance because of their two major features: lightly damped structural dynamics; and nonlinear inertia properties induced by the large motion of articulating sensor heads and antennas. Effective robust control design techniques are needed to satisfy the performance requirements of future space systems in the presence of model uncertainties and nonlinear changes in their inertia properties. In this thesis, the Multiple Model (MM) technique is applied to a plant system which has multiple off-nominal factors including nonlinear inertia properties. Three control design problems are presented to examine the effectiveness of the MM technique: sample designs for a simple plant system; single-input, single-output (SISO) designs for the Middeck Active Control Experiment (MACE); and multiple-input, multiple-output (MIMO) designs for the MACE. A plant model of the MACE test article has two off-nominal factors, i.e. frequency uncertainty in the Z-axis bending modes and nonlinear inertia changes due to different primary payload average angles. In each design problem, LQG compensators are first designed and used as initial compensators in the subsequent MM designs. Through the comparison between LQG and MM compensators, the effectiveness of the MM technique is examined. In every design problem, the MM technique enhances robust stability and performance of an original LQG compensator with small loss in nominal performance. In particular, in the MIMO designs for the MACE, the MM technique substantially improves robust performance for nonlinear inertia properties of the MACE test article. This research reveals the effectiveness of the MM technique for multiple off-nominal factors including nonlinear changes of inertia properties. Thesis Supervisor: Dr. David W. Miller Title: Principal Research Scientist, Department of Aeronautics and Astronautics -~-i~~-YYIII-~^*~I..PCP--YIY-*--YAONWWWONWW* L