Simultaneous estimation of spacecraft position and asteroid diameter during final approach of Hayabusa2 to Ryugu

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.

Self-excited oscillation of spinning solar sails utilizing solar radiation pressure

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.

Solar power sail mission of OKEANOS

The solar power sail is an original Japanese concept in which electric power is generated by thin-film solar cells attached on the solar sail membrane.Japan Aerospace Exploration Agency(JAXA)successfully demonstrated the world’s first solar power sail technology through IKAROS(Interplanetary Kite-craft Accelerated by Radiation of the Sun)mission in 2010.IKAROS demonstrated photon propulsion and power generation using thin-film solar cells during its interplanetary cruise.Scaled up,solar power sails can generate enough power to drive high specific impulse ion thrusters in the outer planetary region.With this concept,we propose a landing or sample return mission to directly explore a Jupiter Trojan asteroid using solar power sail-craft OKEANOS(Oversize Kite-craft for Exploration and AstroNautics in the Outer Solar System).After rendezvousing with a Trojan asteroid,a lander separates from OKEANOS to collect samples,and perform in-situ analyses in three proposed mission sequences,including sending samples back to Earth.This paper proposes a system design for OKEANOS and includes analyses of the latest mission.

Improvement of sail storage and deployment mechanism for spin-type solar power sail

Deployable membrane structures are expected to be used for large area space structures,such as solar propulsion sails,magnetoplasma sails,drag-deorbiting sails,membrane antennas,and solar power sails.They are lightweight and can be compactly stored at launch.One achievement of the Japan Aerospace Exploration Agency(JAXA)was the successful deployment of a 200 m2 sail using centrifugal force in the IKAROS mission,which was the first solar propulsion sail-craft in history.JAXA has long been studying the technology of spin deployment of sail membranes,and is currently planning the spin deployment of a class sail larger than 2000 m2 as the next step in the development of the IK AROS technology.This paper discusses the unexpected behaviors during on-orbit sail deployment by IKAROS,as well as problems with the sail holding method,and proposes an improved sail storage structure and deployment mechanism for the OKEANOS mission.