Optical observations of nonoperational satellites in graveyard orbits

National Institute of Information and Communications Technology (NICT) plans to launch Engineering Test Satellite-9 (ETS-9) in the geosynchronous Earth orbit (GEO) in 2021. When the operation of a GEO satellite is terminated, it must be removed from the GEO protected region and maneuvered to a graveyard orbit. For example, ETS-8, former generation of ETS-9, ended its operation as planned in 2017 and moved to a graveyard orbit. Wideband Inter Networking engineering test and Demonstration Satellite (WINDS) suddenly ended its operation due to a communication error in 2019 and it could not be maneuvered to a graveyard orbit. From the above, we should be aware of the rotation of the objects not only in graveyard orbits but also of objects in GEO to ensure the safety of the operation of ETS-9 and also telecom, earth observation, and navigation satellites. In this study, we carried out optical observations for some of nonoperational satellites including ETS-8 and WINDS using a CCD camera attached to a 1-m telescope. We will report how to select the nonoperational satellites, the results of the optical observations, and the light curves of the satellites using photometry. As a result, we estimate the rotational status of the nonoperational satellites from the light curves.