Yasutaka Otsuji’s scientific contributions

There are so many heavenly bodies, asteroids between Mars and Jupiter. Most of asteroids are not sphere because of small body, and they are like a potato shape. They are called dead heavenly bodies because it is easy to get cold by small body, therefore they have been preserving old information of the solar system. The asteroids are one of the important keys in the study about the growth of the solar system. HAYABUSA that is Japanese engineering spacecraft tried to get the sample of surface of the asteroid. However the inside sample is better than the surface sample because a surface on asteroid was polluted by solar wind. HAYABUSA2 that is the next project following HAYABUSA had a plan to make a crater on the asteroid to get the inside sample by an impactor. The impactor has a special shaped "head" to convey impact energy efficiently. In this study, we designed the form of the impactor's head and evaluated potentiality of a crater formation by the hypervelocity impact experiment.

Space debris is increasing by development of the space environment. The impact of space debris with the International Space Station is considered to be questionable. The model of the space environment is made as one example of the measures. However, the modeling error of the ejecta has been focused recently. It is necessary to do the evaluation examination of ejecta. As for the examination, the size and the depth of crater on a witness plate, and size and velocity distribution of ejecta are measured and evaluated. The distribution of velocity can be measured from tracking fragments using pictures obtained with X-rays. In the measurement of velocity distribution, three flash X-ray tubes are used because two or more pictures are required for measurement of the three-dimensional distributions of space and velocity. However, identification of fragments was difficult in this method because the images irradiated by the different flash X-ray tubes are used for the identification. In this study, we design and develop double anode X-ray tube with different discharging paths so that it can make two irradiations in a short interval. We conduct experiments using the double anode X-ray tube in order to evaluate the performance of the double exposure system.