Terrain relative navigation enhanced with sar for moon’s shadowed regions

This study proposes a terrain relative navigation (TRN) method to estimate spacecraft positions in the shadowed regions of the moon with high precision by combining the camera image and the synthetic aperture radar (SAR) data. TRN, which estimates the position of a spacecraft by comparing the preliminary terrain information stored in a database with the observed terrain, is an effective method of correcting the drift errors of inertial measurement units (IMUs). Optical cameras are primarily used for TRN sensors to observe the terrain; however, shadow images do not have enough characteristic points to match with the database. SAR is a form of radar that can generate high-resolution photo-like images, regardless of light conditions. In this study, we propose the use of SAR as navigation sensors and demonstrate effectiveness of SAR.