Researchers engaged in the development of infrared detector technologies may well benefit from a broader understanding of their products from the perspective of the end-user. An appreciation of how this technology is to be used by system designers, many of whom possess only a rudimentary understanding of quantum physics, is highly germane. Answers to questions like: "What device technology will be employed," "How will the device be used?" and "What are the impacts on signal-to-noise?" are of critical importance. In this paper, some of the fundamentals of hit-to-kill missile defense technology are examined in a largely non-mathematical context. From its "Star Wars" inception during the Reagan administration, to today’s Missile Defense Agency, the core requirement of missile defense has not changed - find the threat and destroy it before it reaches its destination. This fundamental requirement, while conceptually straightforward, is extraordinarily difficult to satisfy, and is almost exclusively dependent on our ability to detect and designate a relatively small, very fast-moving, room-temperature object, at great distances, and usually in a severe environment of shock and vibration further clouded by error and uncertainty. With an obvious bias toward passive IR detection and associated focal plane array characteristics, the flight of a fictitious interceptor is followed from launch to impact. At various points along the interceptor’s trajectory, a "peel the onion" approach is utilized to expose increasingly detailed layers of behavior, including the eventual release of the kinetic kill vehicle, and its autonomous flight to a body-to-body impact with its target. Various sources of error and their impact on the success of the mission are examined, and an overall understanding of the key features of the infrared seeker and its critical role in missile defense are ultimately developed.