Robust Partial Integrated Guidance and Control of Interceptors in Terminal Phase

Integrated guidance and control (IGC) algorithms proposed in the recent literature do not exploit the inherent time scale separation property that exists in aerospace vehicles between rotational and translational motions. Since the amount of body rates needed is explicitly not available in an IGC approach, the design tuning becomes very difficult. Consequently, unless the design is done in an extremely careful manner, this approach may lead to instability of rotational dynamics. To overcome this difficulty, a new time scale separated partial integrated guidance and control design is proposed in this paper. In this design, an outer loop optimal control formulation is solved in a computationally efficient manner using a recently-developed model predictive spread control philosophy. It directly generates the commanded pitch and yaw rates, from an outer loop (formulated in the framework of optimal control theory), whereas the commanded roll rate is generated from a roll stabilization loop. The inner loop tracks the outer loop commands using a nonlinear Dynamic inversion philosophy. In both the loops Six-degree of freedom (Six-DOF) interceptor model is used directly. This intelligent manipulation preserves the inherent time scale separation property between the translational and rotational dynamics, while preserving the benefits of the IGC philosophy. Comparative Six-DOF simulation studies of proposed partial integrated guidance and control (PIGC) scheme with an existing SDRE based one-loop IGC design as well as with a conventional three-loop design shows that the proposed PIGC scheme outperforms both of them. Moreover, to address the problem of modeling inaccuracy, a neuro-adaptive design is augmented to dynamic inversion technique in the inner loop. Numerical results indicate that the proposed approach leads to good performance robustness.