Linearized State-Space Model-Based Attitude Control for Rocket With Four Controllable Fins—Part 1-1: Basic Modeling and Identification

In this study, we present, analyze, and validate a linear state-space model for a simplified rocket with four fins. The model is validated experimentally using a wind tunnel. The proposed model consists of two main elements: a rocket body and fins. The body is represented as a cylinder integrated from infinitesimal sections along the longitudinal direction (x-axis), and each fin is interpreted as an individual rigid body. Applying a linear state space facilitates the use of linear analysis tools, leading to expedient system stability assessment and controller design. Stability analysis of the specific model is performed for validation. The results of the analysis showed that the phase margins of pitching and yawing were 16.9°, and that of rolling was 2.21°. However, the linearized state space carries the risk of discrepancies with the actual dynamics. The model is experimentally validated in a wind tunnel to reduce risk. The rocket model is affixed to a stationary jig in a wind tunnel and has four degrees of freedom. This arrangement allows for the verification of a coupled three-axis rotational model. The results show convergence within an average similarity of 77% in the linear range, confirming the reliability of the model. The validated model can be used for comprehensive analyses including control system design, performance optimization, and robustness analysis of a rocket with four fins in the future.