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Design and implementation of stiffness enhancement of a feed supporting system for the square-kilometer array (SKA) using electrorheological (ER) variable damper is presented in this paper. The feed supporting system consists of a large parallel cable manipulator and a fine-tuning Stewart platform. Hence, the feed supporting system is a large delay system and sensitive to the influence of wind. Furthermore, the adjustment of the fine-tuning Stewart platform will affect the coarse tracking control. Therefore, in order to suppress these disturbances and realize the independent control of the two parallel manipulators, it is necessary to enhance the stiffness of the feed supporting system. The proposed ER variable damper is designed and directly attached to the shaft of the servomotor of the feed supporting system to achieve high servo stiffness and trajectory tracking accuracy. The model of the feed supporting system is first derived, the structure of the variable-viscous ER damper is presented, and then the damping coefficient model is developed. The validation of this stiffness enhancement design of the feed supporting system is demonstrated with position PD control of the feed supporting system. This result has built a solid base for the accomplishment of the high-accuracy requirement of the SKA.