Intelligent systems often operate in a blend of cyberspace and physical space. Cyberspace operations - planning, actions, and effects in realms where signals affect intelligent systems - often occur in milliseconds without human intervention. Decisions and actions in cyberspace can affect physical space, particularly in SCADA - supervisory control and data acquisition - systems. For critical military missions, intelligent and autonomous systems must adhere to commander intent and operate in ways that assure the integrity of mission operations. This paper shows how policy, expressed using an access-control logic, serves as a bridge between commanders and implementers. We describe an access-control logic based on a multi-agent propositional modal logic, show how policies are described, how access decisions are justified, and give examples of how concepts of operations are analyzed. Our experience is policy-based design and verification is within the reach of practicing engineers. A logical approach enables engineers to think precisely about the security and integrity of their systems and the missions they support.