Two-Stage Guidance Law With Constrained Impact via Circle Involute

The mission of simultaneous attack and warhead lethality enhancement requires the constraints on impact time and angle in the guidance design. To this end, a two-stage guidance law considering constrained impact as well as the robustness against external disturbances and heading errors is proposed. The first stage is based on a circle involute geometrical rule that guarantees the desired velocity direction at the involute's end. With this goal achieved, the involute guidance is switched to the guidance of nullifying line-of-sight rate such that near-zero maneuver in the second stage is ensured. To achieve both impact time and angle constraints, a simple parameter determination approach is provided to find explicit solutions for the desired two-stage trajectory. Meanwhile, a robust two-stage guidance law is constructed to implement the geometrical rule, guarantee terminal constraints, and ensure robustness. The proposed technique is easy to implement, in that it does not involve model linearization, time-to-go estimation, and numerical optimization routine. Additionally, the achievable range of different constraints is analyzed considering practical issues such as initial launch angles, initial line-of-sight angles, and acceleration limits. Extensive simulations are carried out in various engagement scenarios under uncertainties and disturbances to validate the effectiveness and robustness of the proposed guidance law.