Design of control system for autonomous airship and experiment

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Airship is a unique vehicle which enables safe and long-duration flight and station keeping. Recently, the interest to unmanned airships has been increasing. Many interesting projects are in progress such as Stratospheric Platform Project, in which the stratospheric airship is utilized as a mobile and low-cost platform for high-speed wireless communication instead of satellites. The position and attitude control is one of the most important component technologies.This study deals with the problem of controlling both the planar position and orientation of an under-actuated airship, which is a nonholonomic system with fewer independent inputs than degree of freedom to be controlled. A robust global stabilization problem is considered for the case where the dynamics of the underactuated airship are subjected to bounded uncertainties. A smooth and time-varying coordinate transformation is utilized to reduce the problem of the airship to that of a linear system. The transformation is independent of the initial state of the system and is nonsingular. The following advantages are obtained. First, the case is dealt with where the dynamics are known and presents a new controller to guarantee exponential stability of the system for any initial states. The design method based on the well-known linear control theory is simple and straightforward. Second, the robust stabilization problem is considered for the uncertain airship with unknown but bounded parameters. The new problem is reduced to the well-known quadric stabilization problem for an uncertain linear system. The design method is simple, and it involves a certain algebraic Riccati equation. Finally, experimental results show the effectiveness of the proposed control system.