Multilayered Metal Insulation (MLMI) for Radioisotope Power System Designs

The Radioisotope Power Systems provide space power and energy storage that enable robotic spacecraft for exploration missions through our solar system. These systems must insulate hot parts from cold using advanced multilayered metal insulation (MLMI) that could reduce system losses. The conventional manufacturing method of MLMI suffers from poor insulative property, long lead time and high manufacturing costs due to manual position of standoffs between thin insulation layers (thickness of 100 micron with a target 100 micron gap). The challenge with achieving the targeted layer separation distance, layer thickness, control density and location of standoffs are critical aspects that effect the insulative property of MLMI. In Phase I, Faraday Technology and Physical Sciences, will address these challenges by demonstration of a manufacturing approach and thermal modelling to fabricate MLMI. Our current target for improved insulative properties is to decrease the thermal conductivity of MLMI from current value of 0.02 W/m·K to < 0.001 W/m·K. The proposed manufacturing approach will also reduce fabrication cost and lead time by combining additive manufacturing and electrochemical technologies to eliminate the manual application of standoffs. We will perform thermal analysis and develop thermal model to refine MLMI design. The Phase I results will be a platform from which Phase II would enable refinement of each manufacturing step and thermal model to improve the insulative properties of MLMI. We envision that by the end of the Phase II our team will develop a method such that completed MLMI packages for Radioisotope Power Systems will be fabricated and tested at NASA Glenn Research Center. In Phase III, we will work with commercialization partners and the NASA to transition and integrate this manufacturing method such that production costs and lead times for high performance MLMI can be further reduced.

Future spacecraft operating to harsh, dark, and cold locations in the solar system will not be able to use solar photovoltaic power. Stirling converters have already been produced by NASA and others that can achieve > 20% conversion efficiency, but MLMI is a critical enabler to bring these convertors into service in the future due to the high temperatures required. Future missions to Jupiter’s moons and other deep solar system objects will therefore require MLMI. The proposed MLMI manufacturing technology will address NASA need for high performance multilayered metal insulation to improve the efficiency of Radioisotope Power Systems. The fabricated MLMI will benefit for radioisotope thermoelectric generator and dynamic power conversion technologies in Radioisotope Power Systems. In these systems MLMI is used to insulate hot parts from cold for minimizing environmental heat losses and maximizing heat transfer from the radioisotope heat source assembly to the power convertor. Despite the prevalence of lithium-ion batteries, micro-engines of less than 1 kW are still being given serious consideration for uses such as unattended sensors, micro air vehicles, and on-the-move battery charging. However, they require excellent insulation to avoid excessive heat losses and low efficiency. Beyond the anticipated use-case for NASA, the radioisotope power systems are developed by DOE and commercial manufacturers for Navy navigational satellites. In addition, U.S. Air Force needs radioisotope thermoelectric generator for its communications satellites in military missions. For these systems to well function, the high performance MLMI with thermal conductivity < 0.001 W/m·K is critical.

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