Terminal guidance algorithm for ramjet-powered missiles

The terminal guidance design problem for a long-range bank-to-turn (BTT) ramjet missile involves a completely coupled pitch-yaw-roll nonlinear dynamics model. Because of these nonlinear dynamics, an optimal solution for acceleration and roll rate commands can be found only by numerical methods for solving two point boundary value problems. Because the roll-rate dynamics of the state-of-the-art missiles is much faster than the rest of the system states, a near-optimal solution is obtained to the BTT guidance problem using multiple timescale techniques. Nonlinear feedback solutions for the acceleration command and roll-rate command are derived. The zero-order slow solution obtained by treating roll rate as infinitely fast, is exactly the optimal guidance law for a skid-to-turn missile. The zero-order fast solution provides the roll-rate command. A first-order analysis corrects the acceleration command for the finite dynamics behavior in bank angle. Simulation results are presented for a representative terminal engagement using this algorithm. Near-zero miss distances are obtained in a noise-free environment.