Design of adaptive sliding mode control for uncertain thrust vectored airship

Airship is lighter than air vehicle filled with lifting gas such as helium or hydrogen and can be operated at a desired altitude with long endurance. Airship can remain airborne for extended period of time1 without spending a lot of energy. Airships have also been proven to be effective in diffcult fiight conditions1 and perform better than conventional aerial vehicles in these diffcult fight conditions like planetary ight forexploration of planets. There has been an increasing interest in recent times in this field due to major applications ranging from defence, scientific exploration2, advertising to even remote monitoring. Above mentioned applications are also the driving factor in research and development of various airship designs and their control systems. These applications require advanced control systems. The uncertain environment in which airships operate makes the task of designing control system very challenging. Linear control methodology such as gain scheduling is simply insuffcient under different operating conditions. Several nonlinear control methodologies dealing with system uncertainties, such as, variable structure control,3,4 robust control,5 feedback linearization control,6,78 and adaptive control9 have been proposed in literature. Most of these control schemes have been implemented on airship models with conventional control surfaces. These control algorithms are very well suited to systems that can be defifined in control affne form and assuming that system’s parameters are known. Considering that airship’s parameters are not exactly known, practical implementation of above control schemes based on conventional formulation may not be directly applicable. Further complexities related to control afinity are encountered while formulating control laws for nonlinear airship models including thrust vectoring capabilities. A MIMO nonlinear adaptive sliding mode control is designed for thrust vectoring airship in this paper. Closed loop simulation results are provided at the end to show the effectiveness of proposed control technique on thrust vectoring airship.