This work aims to solve the problem of relative navigation for space rendezvous and proximity operations using a monocular camera in a numerically efficient manner. It is assumed that the target spacecraft has a special pattern to aid the task of relative pose estimation, and that the chaser spacecraft uses a monocular camera as the primary visual sensor. In this sense, the problem falls under the category of cooperative relative navigation in orbit. While existing systems for cooperative localization with fiducial markers allow full 6-DOF pose estimation, the majority of them are not suitable for in-space cooperative navigation (especially when involving a small-size chaser spacecraft), due to their computational cost. Moreover, most existing fiducial-based localization methods are designed for ground-based applications with limited range (e.g., ground robotics, augmented reality), and their performance deteriorates under large scale changes, such as those encountered in space appl...