The work deals with the topic of spare parts management in a space system. The paper is divided into three parts. The first one is dedicated to the characterization of the system structure and presents the particularities related to the spare-elements procurement. Modelling is the object of the second part. After having exposed the bases of the problem to be solved, a macro-model is introduced. Each of the three elements of an orbital system, namely ground, flying and transport, is then described with a Petri net. Operation specificities of every element are then listed and integrated into the model. A concrete application of this modelling is given in the last part. It concerns the Columbus laboratory of the International Space Station. A representative function is selected and several supply strategies are evaluated.