1 Introduction
Stratospheric airship, a typical lighter-than-air aircraft, has many distinguishing features like long endurance, high payload-to-weight ratio and low fuel consumption. It is viewed as a significant platform for many missions, such as surveillance, earth observation, region navigation, telecommunication, and environmental monitoring[1]. Lots of related researches have been done during the past two decades, the famous ones include “high altitude airships” (HAA) project of the U.S. Lockheed Martin[2], the HiSentinel of the Southwest Research Institute[3], the stratellite of Sanswire[4], the high altitude long endurance airship of NASA[5] and the Korean high altitude platform systems[6]. Due to the airship is an inherently nonlinear and highly coupled multi-input multi-output system with parameter uncertainties, unknown disturbances and actuator saturation, design its flight control system has become a challenging problem.