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. 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 satellite structure. The natural frequency of the satellite should be higher than the value decided by the launching and the satellite should bear the loads during launch. And the satellite should be considered with the value of the moment of inertia and a center of gravity because of stability of position. In this paper, we will propose the design of the satellite whose dimension is 20 centimeters cube. We focused on the trade-off design between minimization of stress condition and the appropriate center of gravity and the moment of inertia under the minimum natural frequency and the maximum mass for optimizing the satellite structures.