A Simple Method for Identifying the Natural Frequency of a Micro Satellite with a Primary Structure Made of Aluminum Alloy

Micro satellites must survive severe mechanical conditions during their launch phase. Usually, the structural design of a micro satellite is performed using the internal stress analysis and the natural frequency analysis, which are based on a finite element method (FEM). The validity of this structural design is evaluated through vibration tests. In an early stage of development, which has a FEM model of a satellite in the process of creation, presumption of the minimum natural frequency of a satellite may be difficult. In this study, a simple method for determining the longitudinal and lateral minimum natural frequencies of micro satellites during the ascent phase was clarified. The structure of the micro satellites used in this research is made of aluminum alloy, and they have a monocoque structure. The Young's modulus and moment of inertia of area used to calculate the minimum natural frequencies were determined using the area ratio of the monocoque structure to the entire satellite. When the method proposed in this study is used, the calculated values agree with the vibration-tested values within 10%. In particular, in the case of W6U-type satellites, the two agree within a range of approximately 2% in the longitudinal direction and approximately 5% in the lateral direction. In the early stages of a satellite structure design when a FEM cannot be created, the proposed method will work effectively as the method of determining the minimum natural frequency. In order to simplify the process of micro satellites development, this paper describes a practical estimation method of the minimum natural frequency for micro satellites.