SPM-Nav: Persistent Space–Portal Memory for Zero-Shot Object Navigation

Zero-shot object navigation requires long-horizon search in unseen environments, where effective decisions depend on both target likelihood and accumulated search history. However, existing spatial representations often leave search evidence and progress fragmented, limiting the persistence and reuse of search experience across revisits. To address this issue, SPM-Nav presents a zero-shot object navigation framework centered on Persistent Space–Portal Memory. Each Space maintains a persistent regional search state that consolidates regional semantics, target evidence, historical observations, negative evidence, and search progress across locations and viewpoints. Portals represent traversal-validated inter-Space transitions and preserve reusable connectivity between regions. Building upon this Memory, Adaptive Space Search, which dynamically adjusts local search effort according to accumulated Space states, reducing redundant inspection while preserving essential inter-region connectivity. SPM-Nav is evaluated on HM3D-v1, HM3D-v2, and MP3D, achieving success rates of 70.6%, 83.8%, and 55.7%, respectively. Component ablations and mechanism analyses further validate the effectiveness of persistent search states, reusable inter-Space transitions, and memory-conditioned adaptive allocation.