Vibration suppression is one of the most important subjects in space structures design or operation.Due to the launch limit of the rocket, such structure might have extremely light weight and it could lead to the small stiffness which is easily vibrated.Moreover, different from the earth, vibration energies are hard to be scattered in the space vacuum environment.These problems could be overcome by vibration control methodologies.According to the case on the earth, the active vibration controls are the most effective one.However, it is very difficult to be operated accurately because they contain the fundamental instability.Another way is the passive vibration controls.Although they are free from the problem of the instability, the effect of vibration suppression is not high.Integrating these methodologies, the semi-active vibration methodologies were proposed as the novel methodology for the vibration suppression in space.Especially, the effectiveness of the energy-recycling type semi-active vibration control method was well studied [1].In designing control systems, such as the layout of actuators, the optimization approach can be utilized.Some methodologies were proposed for designing active or passive control systems [2, 3].However, the optimization methodology for the semi-active vibration control systems has not been studied yet.