The Japanese interplanetary probe Hayabusa2 was launched on December 3, 2014 and the probe arrived at the vicinity of asteroid 162173 Ryugu on June 27, 2018. During its 1.4 years of asteroid proximity phase, the probe successfully accomplished numbers of record-breaking achievements including two touchdowns and one artificial cratering experiment, which are highly expected to have secured surface and subsurface samples from the asteroid inside its sample container for the first time in history. The Hayabusa2 spacecraft was designed not to orbit but to hover above the asteroid along the sub-Earth line. This orbital and geometrical configuration allows the spacecraft to utilize its high-gain antennas for telecommunication with the ground station on Earth while pointing its scientific observation and navigation sensors at the asteroid. This paper focuses on the regular station-keeping operation of Hayabusa2, which is called "home position" (HP)-keeping operation. First, together with the spacecraft design, an operation scheme called HP navigation (HPNAV), which includes a daily trajectory control and scientific observations as regular activities, is introduced. Following the description on the guidance, navigation, and control design as well as the framework of optical and radiometric navigation, the results of the HP-keeping operation including trajectory estimation and delta- $V$ planning during the entire asteroid proximity phase are summarized and evaluated as a first report. Consequently, this paper states that the HP-keeping operation in the framework of HPNAV had succeeded without critical incidents, and the number of trajectory control delta- $V$ was planned efficiently throughout the period.

A solar power sail demonstrator "IKAROS" demonstrated solar sailing technology in 2010. The membrane of the spinning solar sail IKAROS is estimated to be deformed toward the Sun. The deformation was kept even under low spin-rate. Previous studies suggest that curvature of thin-film solar cells on the membrane increases the out-of-plane stiffness by finite element analysis. Shape, out-of-plane stiffness, and natural frequency of membranes have to be predicted for solar sails with thin-film devices, such as thin-film solar cells, dust counters, and reflectivity control devices in order to reduce the margins of sail size and propellant mass against disturbance solar pressure torque acting on the membrane. In this paper, the effect of a curved thin-film device on the natural frequency of a rectangle membrane under uniaxial tension was investigated. Three types of membranes were evaluated: a membrane with a curved thin-film device, a membrane with a flat thin-film device, and a plane membrane. Geometric nonlinear finite element analysis and eigenvalue analysis were conducted to investigate the natural frequencies under varying tension. The simulations were verified by vibration experiments. It was found that under low tension, the natural frequency of the membrane with the curved thin-film device is significantly higher than that of the others and that under high tension, the natural frequency of the membrane with the thin-film device is slightly lower than that of the plane membrane. In addition, parametric analysis on the curvature of the thin-film device shows that natural frequency at low tension is sensitive to the curvature. The eigenvalue analysis of a whole solar sail with the curved thin-film devices also suggests that the curvature remarkably affects the vibration modes. In conclusion, curved thin-film devices have a significant impact on the out-of-plane stiffness of a membrane under low tension.