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Advanced propulsion technologies such as Nuclear Electric Propulsion (NEP) have been partially limited by the mass of thermal rejection systems. NEP was proposed for the Jupiter Icy Moons Obiter (JIMO). Use of novel, lightweight, high-temperature radiator materials, such as those which will be studied in the proposed effort could greatly reduce the mass required for the radiators and help enable NASA exploration missions like JIMO using NEP or other advanced propulsion technologies. Other areas that would potentially benefit from the results of this work include spacecraft heat rejection systems and surface nuclear power. Graphene is a two-dimensional atomic-scale honeycomb lattice made of carbon atoms. This same honeycomb lattice is the basic structural element of carbon nanotubes (CNT) and carbon fibers. While high-quality graphene films are only available in atomic-scale thicknesses, high-conductivity carbon fibers and woven cloth made from CNTs are available commercially in quantity. A novel aspect of the proposed effort is to use graphene-based materials including both high-conductivity carbon fibers and CNT cloth in radiator applications in order to take advantage of several key properties of these materials: low density, high thermal conductivity and anisotropic heat transfer. Modeling results show that a carbon-fiber-based radiator can provide a ten-fold improvement in heat transfer per unit mass compared to the current state-of-the-art molybdenum-based high-temperature radiators. The heat pipe simulator developed in Phase 1 of this effort will be used for testing. A heater is used to simulate the heat pipe envisioned in space. A test article fabricated using the material to be studied is secured to the heater and placed in chamber and heated to the test temperature in a vacuum of about 10-6 Torr.Temperatures in the range of 400 ? 600 :C were tested. Optical diagnostics provide temperature data, including pyrometry and thermal imaging.