The AltiCube+ mission involves the on-orbit assembly of multiple CubeSats to build two radar interferometers. To accomplish this, vision-based relative navigation is required both for target localization during rendezvous and for post-docking relative displacement estimation of structural deformation. This paper presents the design, simulation, and experimental validation of a compact monocular vision-based system capable of fulfilling both functions using a single camera architecture. The proposed system consists of a camera mounted on the chaser spacecraft and an active LED fiducial marker configuration on the target spacecraft. A non-planar marker geometry combined with colour-based segmentation enables robust detection over distances ranging from 10 m to close contact. Sub-pixel marker localization is performed using weighted centroiding and Gaussian fitting, followed by pose estimation through an Efficient Perspective-n-Point (EPnP) algorithm with iterative refinement. The results show that the proposed architecture can support both rendezvous localization and micrometre-scale structural deformation monitoring, providing a compact sensing solution for CubeSat assembly missions. ... Read more