Measurement for the liquid volume in a closed volume under micro-gravity condition is one of important space technologies, for example, in order to know how much water or fuel is left in a container. However, it is difficult to measure the liquid volume in such a situation because liquid and gas system are not clearly separated, rather mixed up. In order to establish an effective and low cost measurement technique, a Helmholtz resonance is applied in the present study. We successfully detected the Helmholtz resonance frequency and its higher order harmonics for a closed container system under micro-gravity condition. The detection of the higher harmonics is indispensable to apply this technique to a large-scale container because the Helmholtz resonance frequency becomes low as increasing the volume of container. The accuracy of this measurement technique is also investigated here. We report the results of micro-gravity experiment and discuss the effectiveness of this measurement technique.
