Abstract
This study assesses the navigation-service availability and observation geometry of a layered cislunar architecture using the BeiDou Navigation Satellite System Phase III (BDS-3) as the Earth-side primary source and distant retrograde orbit (DRO) and near-rectilinear halo orbit (NRHO) nodes as lunar-side augmentation sources. The assessment distinguishes geometrically visible links, beam-accessible links, receiver-detectable signals, and usable navigation observations. Four configurations—BDS-3, BDS-3+DRO, BDS-3+NRHO, and BDS-3+DRO+NRHO—are compared along a representative transfer trajectory and over a grid in the principal Earth–Moon plane. BDS-3 alone provides intermittent support that decreases sharply beyond the near-Earth region. DRO extends coverage and supplies usable observations, whereas the present two-node NRHO configuration provides localized geometric supplementation. The combined configuration yields the largest improvement and reaches 59.7% qualified navigation availability during the late-transfer stage, although the middle-transfer corridor remains weak. The study evaluates service access and geometry rather than end-to-end positioning accuracy.