The idea is to build a temporal multi-layer network connecting the space objects (or groups of objects, like swarms of fragments, that behave as one) in the current population. Once a network model is built, the idea is to study the inter-relationships among objects using a mix of modern network theory and uncertainty quantification to assess the resilience of the space environment and study its possible evolution. The network is multi-layer because we want to model different levels of interaction among objects: communication, physical, service. The communication layer represents the direct exchange of information among objects (active, like int he case of intersatellite links, or passive, like in the case of the detection of an object by another object), the physical layer is the physical interaction (e.g. collisions), the service layer models the shared functionalities of the objects and the service they provide including communications with the ground station and end users. The network is temporal because links and state of each object evolve in time. The use of a network will be used to identify sub-nets, clusters and weak-links and their evolution in time. This representation is also useful to test the effect of the addition or removal of links and nodes and to recognise patterns or structural changes. Appropriate underlying models will be used to study the state of each object and their interrelationships. For example a conjunction model is used to study the possible physical interaction between two objects. In this study it is proposed to build a first multi-layer network and demonstrate the potentialities of this new modelling approach at studying the resilience and sustainability of the space environment.
