Sustainable Satellite Communications in the 6G Era: A European View for Multi-Layer Systems and Space Safety

During the New Space era small countries are also becoming more important players in the space business. While the space activities are rapidly increasing, it is important to make operations in a sustainable and safe way in order to preserve satellite services for future generations. In this survey paper, we discuss the multi-layer networking approaches in the 6G era specifically from the sustainability perspective. We review the most important regulations and international guidelines and revisit a three-dimensional architecture vision to support the sustainability target for a variety of application areas. We then classify and discuss space safety paradigms that are important sustainability enablers of future satellite communications. These include space traffic management, debris detection, environmental impacts, spectrum sharing, and cyber security aspects. The paper discusses also advances towards a planned European connectivity constellation that could become a third flagship infrastructure along with Galileo and Copernicus systems. Finally, we define potential research directions towards the 2030s.