SBIR-STTR Award

Sest, Inc. proposes to perform a detailed evaluation at the both convertor and component levels of a small, low electrical output power (50 to 500 mW) Stirling cycle based convertor utilizing light weight radioisotope heater units (LWRHU) as the heat source. The proposed milliwatt radioisotope Stirling convertor (MRSC) will be optimized for output power with source temperatures in the range of 480 to 560 oK so as to provide electric power at convertor efficiencies in the range of 15 to 20% and sized to make maximum use of the existing LWRHU heat source. These efficiency levels are on the order of 2 to 4 times those of thermoelectric conversion systems. The evaluation processes will incorporate an in-depth evaluation of the structural materials and fabrications techniques required to maximize convertor specific power while at the same time insuring high reliability and long operating life. Due to the unique operating characteristics of convertors of this size a proof of concept linear alternator will be developed and tested during Phase I. At the completion of the proposed Phase I effort a specific final configuration for the detailed hardware design and fabrication in the Phase II effort will be fully defined. In addition a scaling study will be performed identify optimal configurations over the entire power range of interest.

Studies of potential space missions have highlighted the need for very small electric power supplies for a variety of applications. The light weight radioisotope heat unit (RHU) offers a long-life, reliable energy source for such systems which is independent of the surrounding environmental conditions, but a device is needed to convert radioisotope heat into electrical power. In Phase 1, Sest, Inc. investigated and fully defined a complete energy conversion system utilizing a very small Stirling-based convertor powered by a single RHU. It has conversion efficiencies greater than twice that of proposed thermoelectric convertors. Sest, Inc. proposes to complete the detailed design, fabricate, extensively test, and deliver to NASA a functional prototype of a Milliwatt Radioisotope Stirling Convertor (MRSC) system which will clearly demonstrate the performance characteristics of a low power Stirling-based conversion system. The reference MRSC system is designed to produce a net 100 mW or more of useful electrical power from a single RHU over an operating life of 10 years. The overall size of the prototype MRSC package is approximately 80 mm in diameter by 115 mm in length and has an estimated total mass of 250 g, for a specific power of 0.4 We/kg.