Radiator panels are the baseline approach for rejecting waste heat from NASA Fission Surface Power (FSP) systems. The required panels are very large, which makes them challenging to launch, deploy, support, and move. Panel performance may also be degraded by dust, radiation, insolation, and micrometeorite impact. In response, we propose to develop an ultra-compact heat rejection system for use on Mars and other planets and moons with atmospheric gas. This system will rely on forced convection rather than radiation heat transfer. It will decrease power system size and mass dramatically, which will make FSP more affordable and practical. Creare is well suited to succeed because we have a long history developing advanced turbomachines, heat exchangers, and thermal systems for challenging spaceflight applications. During the Phase I project, we will optimize design trades, complete a preliminary design, and conduct bearing evaluation tests. We will then fabricate and test a prototype system during the Phase II project.