Guidance and nonlinear MRAC of a powered air-to-surface weapon with terminal constraint

This paper addresses the guidance and control of a powered air-to-surface weapon where it is desired to hit the target along a preselected terminal flight path. To satisfy the flight path terminal condition, an air-to-surface guidance law is developed which is the solution of a linear-quadratic regulator problem with servo-mechanism action. The guidance law enables satisfaction of the desired flight path angle aloft with the vehicle then proceeding down the flight path to impact. This is in contrast to other guidance laws which satisfy terminal flight path angle constraints asymptotically. To control the vehicle, a nonlinear autopilot based on model reference adaptive control (MRAC) is designed. The autopilot employs model reference observers in both the inner and outer loops to achieve fast yet smooth adaptation. The state-dependent Riccati equation (SDRE) method with integral servo-mechanism action is used to control each of the reference models. A detailed six-degrees-of-freedom (6-DOF) simulation is used to evaluate the effectiveness and robustness of the guidance law and autopilot and simulation results are presented.