Students of the MSc course in Astronautics and Space Engineering 2005/06 at Cranfield University took GeoSAR as one of their group projects. This report summarises their findings. GeoSAR is an initial feasibility study for a satellite carrying a passive bistatic radar receiver based in geosynchronous orbit. The feasibility of the radar concept has already been established (e.g. through the work of Prati et al. of Politecnico di Milano) but no designs have yet been published for a satellite to support the mission. This project develops an outline design of the spacecraft and confirms its feasibility within a (conservative) mass budget of approximately 300 kg. Mission drivers are the radar antenna diameter and the station-keeping propulsion required for a design life of 15 years. Technologies such as inflatable structures and (field- emission) electric propulsion are used to reduce the spacecraft's mass. An outline cost estimate for the mission suggests that a GeoSAR mission would be significantly cheaper than conventional low-Earth orbit radar satellites to achieve similar capability in terms of rapid-response imaging and interferometry. In several areas the GeoSAR design is conservative and it is plausible that on further iterations of the design the cost and mass can be reduced. This suggests that among options for future Earth observation missions, GeoSAR deserves serious consideration.