1. Accuracy analysis of the two-loop attitude control system on the Sich spacecraft

Annotation: The development of the domestic Sich satellite family for Earth observation missions requires a radical increase in the stabilization accuracy of optoelectronic payload. Contemporary requirements for spatial resolution impose strict limitations on the angular oscillations of the satellite platform. Due to a trade-off between maximum torque and engine sensitivity, traditional stabilization systems consisting of a single loop of reaction wheels cannot simultaneously provide high dynamics during rapid programmed maneuvers and minimal tracking errors during imaging. Implementing a two-loop reaction wheel confi guration, which integrates a primary loop and a precision loop, is critical as it minimizes angular errors under the strict power constraints of onboard systems. This paper discusses a comprehensive mathematical model developed for the attitude control system of the Sich satellite. The model’s key feature is the mathematical description of the interaction between two levels of actuators: a primary loop of large reaction wheels for quick dynamic maneuvers, and a precision loop of small wheels for high-accuracy microdisturbance compensation and fi nal stabilization. The object of the study includes transient attitude control processes across various operational modes: initial detumbling after separation, long-term maintenance of the desired three-axis attitude, rapid programmed rotations, and pointing to the ground station during data downlink. The paper off ers new algorithms that are based on the separation of control signals’ frequency to achieve the optimal allocation of control torques between the two loops of actuators. Additionally, the paper synthesizes a control law for the continuous momentum desaturation of the reaction wheel system using magnetorquers that interact with the geomagnetic fi eld, preventing actuator saturation. Mathematical simulation results fully confi rm the eff ectiveness of the proposed two-level confi guration of the actuators. It reduces the amplitude of low-frequency angular oscillations of the satellite during imaging. The joint operation of both loops meets the stringent requirements for precise orientation while signifi cantly reducing the detumbling period and minimizing power consumption, thereby extending the satellite’s operational lifespan.