Results of plasma measurement in HTV during ISS approach phase

H-II Transfer Vehicle, HTV, is Japanese spacecraft docks to the international space station, ISS, for the purpose of logistic supply and waste disposal. The HTV is the series spacecraft, and its size is 10 m in length and 4 m in diameter. The sixth HTV, HTV-6, is equipped with the instrument to measure the potential of HTV-6 against ambient plasma, and the number density of electron. The ISS is equipped with the instrument to measure the plasma characteristics of ionosphere. The instruments on two spacecraft can provide us the in-situ measurement data for different position. In this presentation, we focus on the plasma bubble measured by the two instruments. The HTV-6 encountered the plasma bubble on 0430-0600 11 December 2016. The HTV was fling on same orbital plane as the ISS, and approaching to the behind of ISS. The altitude of HTV and ISS were 295 km and 400 km, respectively. The differential altitude of both spacecraft is approximately 100 km. The HTV passed the latitude / longitude where ISS passed several minutes later. In the above time period, the HTV measured the depletion of electron density. As the signal of GPS receiver on HTV-6 also showed the disturbance, we evaluated the cause of depletion of electron density as plasma bubble. The ISS measured the depletion of electron density after HTV measured. As the instrument on the both spacecraft measured the depletion of electron density for approximately 10 minutes, we measured the plasma bubble in the space with approximately 80 km to the latitude direction, and 100 km for the height. The authors expect the in-situ measurement data obtained from two satellite can be potentially useful for the research about ionospheric plasma.