Nonlinear, hybrid bank-to-turn/skid-to-turn missile autopilot design

Abstract

Nomenclature A full-envelope, hybrid bank-to-turn (BTT)/ skid-to-turn (STT) autopilot design for an air-breathing air-to-air missile is carried out using the state-dependent Riccati equation (SDRE) technique of nonlinear control. Hybrid BTT/STT autopilot command logic is used to convert the guidance law's commanded acceleration to angle of attack, side-slip, and bank angle reference commands for the autopilot. In the midcourse and terminal phases of flight, BTT control is employed to prevent engine flameout. In the endgame, STT control is employed to increase response time. As the missile approaches the endgame phase and passes a preset time-to-go threshold, STT commands are ramped into the BTT commands over a preselected time interval to attenuate transient responses. During this interval, the missile is flying hybrid BTT/STT. An SDRE nonlinear outer-loop controller converts the angle-of-attack, sideslip, and bank angle commands to body rates commands for the inner loop. An inner-loop SDRE nonlinear controller converts the body rate commands to fin commands. Hard bounds on the fin deflections are embedded within the inner-loop controller dynamics ensuring that the autopilot only commands deflections that are achievable. The nonlinear design is evaluated using a detailed six-degrees-of-freedom simulation.