LQG Controller for Load Relief in theCombined Rigid Body and Flexibility Model of a Launch Vehicle

Abstract

A launch vehicle experiences considerable disturbance moment during the atmospheric phase of ascent, resulting in axial and lateral loads. It adversely affects the structural integrity of the vehicle. The wind is a major source of disturbance, especially during the maximum dynamic pressure region of flight when wind velocities produce the largest vehicle bending moments. The wind induces an additional angle of attack that contributes significantly to the aerodynamic and hence structural loading on the vehicle. The job of a load relief control system is to minimize the effective aerodynamic loading on the vehicle as well as maintain the resulting trajectory dispersions within allowable limits. So as to make sure that the trajectory dispersions stay within affordable limits, load relief is generally applied during the maximum dynamic pressure period. However, a dedicated sensor for measuring the angle of attack increases the overall mass of the vehicle, poses additional design constraints and is not an economical option. In that regard, an estimator-based load relief control is the most feasible option. This paper discusses the design of a load relief controller using LQG technique for the 5th order combined rigid body and flexibility model of a launch vehicle for accomplishing this objective.