"Space exploration is one of Europe’s priorities. Nuclear propulsion and power sources are “…essential and enabling key assets for a significant number of exploration missions…” (2005 European WG report on Nuclear Power Sources for Space) and can thus be considered as key technologies for deep-space exploration in Europe, Russia, and the USA. On the other hand, this technological development requires important financial efforts. Such a development should thus take place in the frame of an international collaboration as this has been the case, e.g. for the International Space Station. Among concepts that allow going to Mars are the very high power chemical propulsion or the nuclear propulsion. Megawatt level Nuclear-Electrical Propulsion is more interesting than chemical propulsion (higher payload ratio, cheaper in the long term, reduced launch mass and number of launchers, faster transit). Robotic science missions to the outer solar system could be used as test-beds and would benefit from this technology (faster missions or heavier payload), as well as surface power sources for In-Situ Resource Utilization and life support. The aim is to develop a European roadmap enabling such a program, taking advantage of each international partner's specific skills. The role of every partner will be based on its technical and economical capabilities, ambitions, interests and national policy. The objective is to set up an international network and adequate coordination means with future potential partners, leading to the establishment of a common roadmap involving all identified stakeholders, that will be driven by technological choices to suit long term objectives for space exploration. It will define common research objectives, draw-up research agenda and initiate research alliances. This project will help Europe invest in the research areas for which funding support will be particularly effective to ensure a key role for Europe in space exploration."