Terrestrial and space systems may be differentiated by their finalities in a Circular Economy (CE) perspective. On the one hand, CE for space systems maximises the efficiency of materials and energy loops to allow long-term space travel and keep the crew alive and in good health. Impacts (like pollution) on the ‘external world’ (space, the Moon, or Mars surface) are not an issue by themselves; economic issues are predominant during the design of space systems but are not considered during the missions themselves. On the other hand, CE for terrestrial systems also maximises the efficiency of materials and energy loops but with additional objectives. Those are to minimise the use of resources and the environmental impact while maximising the system’s economic performance on its entire life cycle; the environmental impact on the external and natural world is as important as the economic performance. Moreover, more and more CE methods and tools for terrestrial systems also include a social dimension to maximise value creation for all the stakeholders, far beyond crew health issues considered for space systems. In this sense, designing and monitoring more circular systems – whether terrestrial or space systems – implies the ability to measure and analyse flows and impacts at different scales and for different purposes. Beyond historical tools such as Material Flow Analysis (MFA) and Life Cycle Assessment (LCA), Circularity Indicators represent an emergent field of research for about ten years. Digitalisation is another promising field of research for CE. It studies how to better (more dynamically and close to real-time) model, simulate, and monitor industrial systems using data gathered along the value chain and digital tools embedding circularity indicators (all along with technical and economic ones). In this particular context, our recent and ongoing work in collaboration with the MELiSSA project shows a clear interest in developing a simulation platform that could model and connect the different parts of a technological space or terrestrial system. Such a platform could be based on dynamic modelling of materials and energy flows sent through the different parts of the system, for example, thanks to Dynamic Material Flow Analysis (MFA) or System Dynamics. It could also be coupled with relevant circularity indicators selected from extensive existing databases (extending, for example, the ALiSSE criteria, which are more suitable for space systems). The simulation of multiple dynamic scenarios could allow studying long-term performances and impacts. In this presentation, we propose to give an overview of these two emerging and promising fields of research – circularity indicators and digitalisation - toward a circular economy and to expose how they can be combined to better design and monitor more circular terrestrial and space systems. We will explore existing literature and ongoing projects that may inspire MELiSSA partners and foster collaborations. Finally, we will show how we envisage bridging the gap between Systems Engineering and Circular Economy, which are often uncorrelated disciplines.