Recently the development of the small satellite becomes active. In general, small satellites are expected to be developed faster and cheaper than the large satellites. The launching cost of the piggyback satellite is low, and then a cost of a piggyback satellite is often decided by weight. Therefore it is important to reduce the weight of satellite for cost. Considering the severe mechanical environment of launching, we have to design of satellite structure. The natural frequency of the satellite should be higher than the value decided by the rocket and the satellite should withstand the loads during launch. In this paper, we will propose the design of the satellite whose dimension is 20 centimeters cube. The satellite supposed to be launched by H-2A rocked and we focused on the trade-off design between minimization of mass and maximization of natural frequency under the maximum stress condition for optimizing the satellite structures.