On-orbit proximity operations are becoming increasingly important for both present and future missions, particularly OOS (On-Orbiting-Services) and ADR (Active-Debris Removal). In this framework, a high-accuracy estimation of the relative pose (position and attitude) between spacecraft is mandatory to successfully and safely achieve inspection/observation, rendezvous and docking phases. Spacecraft pose estimation is defined as the capability of an active spacecraft (chaser) to estimate the relative position and attitude of a known non-cooperative one (target). It involves both theoretical and technological challenges related to the search for the most suitable sensor architecture and algorithm solutions. On this behalf, visual navigation consists of estimating the pose of the target from a single image.