This paper presents the optical navigation results of the asteroid explorer Hayabusa2 during the final rendezvous approach phase with the asteroid Ryugu. The orbit determination of Hayabusa2 during the cruising phase uses a triangulation-based method that estimates the probe and asteroid orbits using the directions from which they are observed. Conversely, the asteroid size is available as optical information just prior to arrival. The size information allows us to estimate the relative distance between the probe and the asteroid with high accuracy, that is strongly related to the success or failure of the rendezvous. In this study, the relative distance and asteroid size in real space are simultaneously estimated in real time by focusing on the rate of change of the asteroid size observed in sequential images. The real-time estimation results coincided with those of precise analyses performed after arrival.

The present paper proposes a control method to excite spinning solar sail membranes for three-dimensional use. Using optical property switching, the input is given as the change in magnitude of the solar radiation pressure. The resonance point of this system varies with the vibration state due to its nonlinearity and the change in equilibrium state. To deal with this, a state feedback control law that automatically tracks the resonance point is developed in the present study. The proposed method enables decentralized control of the actuators on the sail, each of which determines the control input independently using only the information of vibration state. The proposed method is validated using numerical simulations. The results show that the nonlinear system behaves differently from the linear system, and the vibration grows using the decentralized control regardless of resonance point variation.