A Satellite Backbone Network is a high-capacity communications infrastructure that uses satellites, particularly in low Earth orbit constellations, to carry large volumes of traffic between geographically distributed nodes, complementing or replacing terrestrial fiber backbone links. Inter-satellite optical links enable high-throughput, low-latency routing across the constellation without ground relay. Research challenges include dynamic topology management, seamless handover, integration with terrestrial optical networks, and traffic engineering across hybrid space-ground architectures.