Convolutional-Neural-Network-Based Autonomous Navigation of Hera Mission Around Didymos

The European Space Agency (ESA)’s Hera mission requires autonomous visual-based navigation in order to safely orbit around the target binary asteroid system Didymos and its moon Dimorphos in 2027. Nevertheless, the performance of optical-based navigation systems depends on the intrinsic properties of the image, such as high Sun phase angles, the presence of other bodies, and, especially, the irregular shape of the target. Therefore, to improve the navigation performance, thermal and/or range measurements from additional onboard instruments are usually needed to complement optical measurements. However, this work addresses these challenges by developing a fully visual-based autonomous navigation system using a convolutional-neural-network (CNN)-based image processing (IP) algorithm and applying it to the detailed characterization phase of the proximity operation of the mission. The images taken by the onboard camera are processed by the CNN-based IP algorithm that estimates the position of the geometrical centers of Didymos and Dimorphos, the range from Didymos, and the associated covariances. The results show that the developed algorithm can be used for a fully visual-based navigation for the position of the Hera spacecraft around the target with good robustness and accuracy.