Robust gain scheduled longitudinal autopilot design for rockets during the sustaining phase

Abstract

This paper explores the design of a pitch axis load factor autopilot for a class of rockets during the sustaining phase. The existence of the thrust enhances the time-variant characteristic of the rockets mathematical model which contributes to the difficulty of the autopilot design. According to the longitudinal dynamic model of the 122 mm rocket and the design goal of cruising at a constant height, a global autopilot is designed via robust gain scheduling technology regarding time as the scheduling parameter. In contrast to the full-order and the reduced-order mixed sensitivity ${\mathcal{H}}_{\infty }$ linear compensators, it is a fixed-structure controller consisting of one proportional-integral, two proportional controllers and one first-order filter. With respect to the flight condition uncertainty throughout the sustaining phase, the robust stability is analyzed based on the structured singular value. Simulation results show that the autopilot is insensitive to measurement noises and that the flight path of the rocket can be held at a constant height in different launching angles with an additional simple height controller.