Missile longitudinal autopilot design using a new suboptimal nonlinear control method

A missile longitudinal autopilot is designed using a new nonlinear control synthesis technique called the θ-D approximation. The particular θ-D methodology used is referred to as the θ-D H₂ design. The technique can achieve suboptimal closed-form solutions to a class of nonlinear optimal control problems in the sense that it solves the Hamilton-Jacobi-Bellman equation approximately by adding perturbations to the cost function. An interesting feature of this method is that the expansion terms in the expression for suboptimal control are nothing but solutions to the state-dependent Riccati equations associated with this class of problems. The θ-D H₂ design has the same structure as that of the linear H₂ formulation, except that the two Riccati equations are state dependent. Numerical simulations are presented that demonstrate the potential of this technique for use in an autopilot design. These results are compared with the recently popular SDRE H₂ method.