High-Emissivity CVD Dendritic Rhenium Coatings for NEP Radiator Panels, Phase II

Nuclear-electric propulsion (NEP) can significantly reduce mission durations for space exploration by providing substantially greater propulsion efficiency over chemical propulsion. NEP development is dependent on advances in several key technology areas, one of which is the primary heat rejection subsystem, which will account for a significant portion of the total spacecraft mass. Improved radiator panels, with lighter weight and higher emissivity, are needed, enabling reduced panel size for a reduction in the overall vehicle mass and more effective heat rejection for a more efficient propulsion system. The state-of-the-art space radiator material system uses carbon/carbon (C/C) or titanium panels with integrated titanium heat pipes. To increase radiator emissivity, Ultramet is depositing a thin, highly emissive dendritic rhenium coating on carbon and titanium with minimal effect on overall weight. In Phase I, coated coupons of representative carbon and titanium materials were sent to the University of Michigan for characterization and testing.nbsp;Coating survivability was demonstrated through exposure at various angles to ion bombardment from a Hall thruster ion plume, with microscopic imaging and emissivity measurements done before and after exposure. The dendritic microstructure and high emissivity of the rhenium coatings were unaffected after ion exposure in most cases. In Phase II, Ultramet will team with ThermAvant Technologies to demonstrate the increased heat rejection provided by the dendritic rhenium coating on additively manufactured titanium, diffusion-bonded titanium plate, and C/C subscale radiator panels with integrated titanium heat pipes. Coated subscale panels of each material will be fabricated and tested in relevant in-space operating conditions in a thermal vacuum chamber at NASA Glenn Research Center. A full-scale radiator panel design and manufacturing plan will be developed based on the results of the demonstration testing.