Description: 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. 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.

Benefits: Enabling human Earth‐to‐Mars round trip mission durations of less than 750 days is a key goal for NASA. Nuclear power provides the means of achieving this goal, but operating a nuclear reactor in space requires the reactor to be smaller and more compact than ground-based systems. Waste heat must be rejected into space through radiators. The proposed radiator panels will provide a lightweight, high-efficiency, high thermal conductivity advancement in heat removal for cislunar, Mars, and outer solar system missions, both crewed and robotic.

The proposed technology will be ideal for existing and new electric propulsion systems used for station-keeping and attitude control of commercial and military spacecraft. Terrestrial applications include plasma processing for a wide range of product manufacturing and services, pulsed power devices, and material characterization facilities utilizing high electron currents.