<p>Space activity is gradually moving from occasional missions to sustained industrial operations. Space-based manufacturing, orbital servicing, lunar resource extraction and in-situ resource utilisation (ISRU) are no longer distant ideas. They are becoming part of legal, commercial and technological planning for the next phase of space development. These activities will create long and complex supply chains connecting Earth, low Earth orbit, cislunar space, lunar orbit and the lunar surface. Such supply chains will depend on critical minerals, advanced manufacturing, launch systems, autonomous technologies, robotics, artificial intelligence, communication networks and national licensing frameworks. They will also create risks that are difficult to manage through ordinary terrestrial compliance models. This paper studies supply chain due diligence as a practical governance tool for space-based manufacturing and lunar resource extraction. It argues that due diligence in cislunar operations must go beyond voluntary corporate responsibility. It must be linked with state authorisation, continuing supervision, traceability, environmental care, cybersecurity, AI governance, debris mitigation and long-term sustainability. The paper maps the major stages of the cislunar supply chain and explains how terrestrial due diligence models can be adapted to the special conditions of outer space. It also examines the relevance of space treaty principles, national space resource laws, sustainability guidelines and emerging regulatory practices. The central argument of the paper is that responsible cislunar development requires measurable and reviewable due diligence standards from the beginning. A licensing system that only asks whether a mission is technically possible will remain incomplete. Future space governance must also ask whether the mission is lawful, traceable, resilient, environmentally careful and capable of being supervised. The paper therefore proposes a Cislunar Due Diligence Cycle and a benchmarking framework to help regulators, operators and investors assess risks across the full supply chain. It concludes that early adoption of due diligence can help prevent terrestrial patterns of extraction, opacity and environmental neglect from being repeated beyond Earth.</p>