Preliminary studies have been done on the use of Multi-Layer Insulation (MLI) as well as bulk aerogel insulation for Stirling convertors used on the Advanced Stirling Radioisotope Generator (ASRG). These studies show the potential benefits of MLI for space vacuum applications in reducing generator size and increasing specific power (W/kg) as compared to the baseline Microtherm HT insulation. Further studies are currently being conducted at NASA Glenn Research Center (GRC) on various candidate MLI foils and spacers as well as aerogel composites.
The Thermal Materials project also investigates heat transfer methods to improve performance and life of RPS systems with emphasis on Stirling convertor application testing.
- Liquid Metal Heat Pipes for GPHS Thermal Management – Variable Conductance Heat Pipes (VCHP) provide a potential method to control Stirling convertor heat input during nominal and fault conditions. In case of single convertor failure, the VCHP enables necessary rejection of the excess heat to the housing as a passive safety feature. VCHP technology could potentially be combined with Multi-Layer Insulation (MLI) to provide effective hot-end insulation with over-temperature control.
- Water Heat Pipes for Efficient Cold-Side Heat Transfer – Potential replacement of the Cold Side Adapter Flange (CSAF) with a flat plate heat pipe with micro-channels. The proposed technology would use a Radial Core Heat Spreader (RCHS), a passive thermal control system, to couple the convertor to the heat rejection system and provide up to 10 times the thermal conductance compared to the current Advanced Stirling Convertor (ASC) CSAF. This thermal enhancement can offer increased structural strength, higher efficiency, and a greater thermal conductance than the current CSAF.