“Space-Data Routers” (SDR) will allow Space Agencies, Academic Institutes and Research Centers to share space-data generated by a single or multiple missions, in a natural, flexible, secure and automated manner. We develop a communication overlay modeled according to thematic context of missions, Ground Segment topological distribution, Agency policies and Application restrictions and requirements. We realize our model through the development of Space-Data Routers: a (Delay-Tolerant Networking) DTN-enabled device that: (i) incorporates the Space Agency administrative instructions and policies for data dissemination and resource utilization and (ii) integrates the DTN protocol stack with application, network and link layer protocols. We pay particular attention to ESA roadmap for Interplanetary Communications and implement a communication scheme that scales natively with future deployments in Space. In essence, we promote the ultimate objective of most missions, which is to return space data, which, in turn, will be disseminated and exploited for the benefit of human scientific knowledge. Space-Data Routers form an overlay suitable for exploiting space data efficiently, which is, by definition, a major objective of all space missions and probably the most significant failure today.