LOS Rate Calculation for Roll-spinning Missiles With a Two-axis Seeker

초록

In a roll-stabilized missile using a two-axis gimbal seeker, boresight error is proportional to the LOS rate. However, in a roll-spinning missile, the boresight error of the seeker is not proportional to the LOS rate due to the missile's roll maneuver, making use of a two-axis gimbal seeker challenging. To address this, a three-axis gimbal is often used, which increases the complexity, weight, and cost of the gimbal system. This paper proposes a method to calculate the LOS rate in a roll-spinning missile using a two-axis gimbal seeker, considering the coupling effect from the rotation of the missile and the gimbal. First, a LOS coordinate system is defined by rotating the x-axis of the inertial coordinate system in the order of azimuth and elevation angles, so that the x-axis points to the relative position of the target. Then, the cross product of the LOS rate and the relative position is the same as the cross product of the angular velocity of the previously defined LOS coordinate system and the relative position. Using the properties of vector cross products and the geometric relationship of vectors, the LOS rate can be calculated. The angular velocity of the LOS coordinate system can be derived using kinematic relationships of rotation between coordinate systems, including the body frame and gimbal frame, compensating for the coupling effect from the rotation of the missile and the gimbal. However, the equation calculating the angular velocity of the LOS coordinate system includes the boresight error rate of the two-axis gimbal seeker, which cannot be measured. The angular velocity of the LOS coordinate system can be calculated using an alpha-beta filter, which estimates the boresight error rate, along with the kinematic relationships between coordinate systems and this estimated rate. The proposed method for calculating the LOS rate allows the calculation of the LOS rate using two-axis mounted seeker in a missile without the need for roll stabilization, considering the coupling effect from the rotation of the missile and the gimbal. Through 6-DOF (Degree of Freedom) simulation, the error between the LOS rate calculated using the proposed method and the actual LOS rate being small is confirmed, and the impact on guidance commands is verified. When calculating the guidance commands of a roll-spinning missile, the LOS rate calculated using the proposed method is applied to verify the performance of the method. The method proposed in this paper enables the calculation of the LOS rate in a roll-spinning missile using a two-axis gimbal without the need for additional devices. © © (2024) by Engineers Australia. All rights reserved.

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