High-Emissivity CVD Dendritic Rhenium Coatings for NEP Radiator Panels

Nuclear-electric propulsion (NEP) provides a means of significantly reducing mission durations for space exploration. NEP is able to provide substantially greater propulsion efficiency over chemical propulsion systems. The advantage of NEP is that it requires little propellant, is not reliant on solar proximity/orientation, and can provide thrust for extended periods of time. Further, NEP can be combined with chemical propulsion to provide high specific impulse (Isp)/low-thrust and low-Isp/high-thrust propulsion respectively, depending on mission and spacecraft requirements. One of the largest obstacles to overcome for more efficient space travel is the total vehicle mass. NEP development is dependent on the development of several key technology areas, one of which is the primary heat rejection subsystem, which requires a highly emissive radiator. In a NEP vehicle, the radiator will account for a significant portion of the total vehicle mass. Improved radiator panels are needed, allowing for either a reduction in the overall vehicle mass as the panel size is reduced, or a more powerful propulsion system as waste heat is more effectively managed. The current state-of-the-art space radiator material system uses carbon/carbon (C/C) composite panels that are built around or bonded to titanium alloy heat pipes. To increase the emissivity of the radiator with minimal effect on the overall weight, Ultramet proposes to apply a thin high-emissivity coating to the C/C panels. In this project, Ultramet will use chemical vapor deposition (CVD) to deposit a thin, highly emissive dendritic rhenium coating on carbon and titanium substrates to demonstrate feasibility. The emissivity and ion bombardment survivability of the dendritic coating applied to carbon and titanium substrates will be characterized through testing.