"Radiator advancement is perhaps the most critical thermal technology development for future spacecraft and space-based systems. Since radiators contribute a substantial portion of the thermal control system mass." –Thermal Management Systems Roadmap (Technology Area 14), NASA 2012 Nuclear electric propulsion (NEP) is a promising option for high-speed in-space travel due to its high energy density of nuclear fission power source and efficient electric thrusters. Lightweight radiator technology is an enabling element for NEP. Game-changing propulsion systems are often enabled by novel designs using advanced materials. Promising new technologies may require high operating temperatures and could benefit from use of advanced lightweight materials in a heat rejection system. Radiator performance dictates power output for nuclear electric propulsion (NEP) systems. Pitch-based carbon fiber materials have the potential to offer significant improvements in operating temperature, thermal conductivity, and mass properties. We propose to continue previous radiator research through the efforts of a visiting researcher on a fellowship from NASA HQ. The objective is to advance the TRL of the lightweight radiators from 3 to 4-5. This will involve using sodium heat pipes which are of a scalable size, high temperature brazing material, and dense carbon fiber mats. This project has shown that high thermal conductivity carbon can be woven into an effective thermally radiating mat and that it can be attached with good thermal contact to heat pipe shell materials. We have shown that the carbon fiber radiators may have a dissipative specific power (kW/Kg) that is an order of magnitude greater than the best conventional high-temperature fin material. Advancing this technology could be enabling for space nuclear power systems that require lightweight, high-temperature radiators. The work for the coming year covered by this proposal will take this further by: - Building and testing higher fidelity test articles using sodium heat pipes and industrially woven fiber textile - Continuing to characterize fin emissivity, thermal conductivity, and power rejection, density, and thickness as a function of weaving method and fin dimensions. - System modeling to predict mass and required radiator surface area savings over conventional materials.