In this paper, an improved bank-to-turn (BTT) command allocation strategy is investigated for TH-Ⅲ (a small solid rocket) to track the standard trajectory. In a BTT system, the angle of attack and roll angle are principally used to guide the rocket, which are usually calculated through a polar converting logic (PCL) from the acceleration commands generated by traditional skid-to-turn (STT) guidance command in the prevalent guidance law. Whereas, the used arctangent operation in PCL would result in a mathematical singularity problem when the vertical acceleration command approaches zero. To circumvent this problem, an improved shortest path adjustment method in roll channel is proposed to calculate the roll angle command in the body coordinate frame. And when the vertical acceleration command approaches zero, an auxiliary STT maneuver is introduced to ensure providing adequate maneuver ability for vehicles in any directions. In order to decrease the magnitude of abrupt change of roll angle, two reasonable precondition is proposed for the maneuver form switch. Finally, the robustness and validity of the proposed allocation strategy are demonstrated through the Monte-Carlo numerical simulations under parameters uncertainties.
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