This thesis explores the growing intersection between civil and military space activities by investigating the concept of dual use in satellites. These systems can serve both commercial and defense purposes. The aim is to move beyond the traditional binary distinction between civil and military missions, by developing a model capable of measuring and classifying the degree of dual use in existing satellite systems. To achieve this, a spectrum-based model was designed through the creation of a Dual-Use Index which allows to estimate the real dual-use potential of a satellite. After defining the problem and reviewing the current policy framework, the typical features of military satellites were analyzed as a benchmark.