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Optimal Control of Roll-Pitch Seeker with Singularity Avoidance

In order to provide guidance information, various types of optics seekers are incorporated in most modern missiles. A seeker moves independently of the missile dynamics to track a target image, providing the target information to the missile. Among them, two-axis seekers are widely used because they can rotate freely toward the target. According to the direction of rotating axes, the two-axis seekers are categorized into yaw-pitch and roll-pitch types. The yaw-pitch gimbal structure has been researched widely since it provides an intuitive way to track the target. On the other hand, due to smaller size with a larger gimbal angle, the roll-pitch structure is actively studied and widely applied to missiles recently. Despite the advantages, the inherent structural characteristic of the roll-pitch seeker has made the research relatively late. When the target is aligned with the missile axial direction, a singularity occurs at which the roll angle of the gimbal becomes indefinite. Furthermore, when the target moves around the singular point, the roll gimbal command angle abruptly changes, dissipating control energy while showing an abrupt oscillation in gimbal response. This paper analyzes the singularity problem in the roll-pitch seeker and introduces an optimal control method to properly relieve the problem.