Adaptive Control of Hypersonic Vehicles in Presence of Actuation Uncertainties by Amith Somanath

The thesis develops a new class of adaptive controllers that guarantee global stability in presence of actuation uncertainties. Actuation uncertainties culminate to linear plants with a partially known input matrix B. Currently available multivariable adaptive controllers yield global stability only when the input matrix B is completely known. It is shown in this work that when additional information regarding the structure of B is available, this difficulty can be overcome using the proposed class of controllers. In addition, a nonlinear damping term is added to the adaptive law to further improve the stability characteristics. It is shown here that the adaptive controllers developed above are well suited for command tracking in hypersonic vehicles (HSV) in the presence of aerodynamic and center of gravity (CG) uncertainties. A model that accurately captures the effect of CG shifts on the longitudinal dynamics of the HSV is derived from first principles. Linearization of these nonlinear equations about an operating point indicate that a constant gain controller does not guarantee vehicle stability, thereby motivating the use of an adaptive controller. Performance improvements are shown using simulation studies carried out on a full scale nonlinear model of the HSV. It is shown that the tolerable CG shifts can be almost doubled by using an adaptive controller as compared to a linear controller while tracking reference commands in velocity and altitude. Thesis Supervisor: Dr Anuradha Annaswamy Title: Senior Research Scientist, Dept of Mechanical Engineering Acknowledgments I would like to thank Dr. Anuradha Annaswamy for her invaluable guidance, motivation and support throughout the course of my master's program. I would also like to thank my lab mates Travis Gibson, Megumi Matsutani, Manohar Srikanth and Zac Dydek for making my stay at the lab enjoyable. I would like to express my sincere gratitude to my parents for their continuous support and encouragement without which this work would have not been possible. This thesis is dedicated to them. This work is supported by NASA award NNX07AC48A