NASA SBIR 2004 Solicitation


PROPOSAL NUMBER: 04 E2.06-8702
SUBTOPIC TITLE: Energy Conversion for Space Applications
PROPOSAL TITLE: Milliwatt Radioisotope Stirling Convertor

SMALL BUSINESS CONCERN (Name, E-mail, Mail Address, City/State/Zip, Phone)
Sest, Inc.
18000 Jefferson Park, Suite 104
Middleburg Heights, OH 44130-3440

PRINCIPAL INVESTIGATOR/PROJECT MANAGER (Name, E-mail, Mail Address, City/State/Zip, Phone)
L. Barry Penswick
18000 Jefferson Park
Suite 104, OH 44130-3440

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.

The proposed low power generating system, operating at power outputs in the range of 50 to 500 mW, has a number of potential NASA and US government agency applications. It provides small, robust stand-alone power systems for sensors and communication equipment integrated into single unit. The significantly greater efficiency of the proposed system will minimize the number of LWRHU, or related, heat sources dramatically reducing system cost and minimizing environmental concerns with the use of isotope heat sources. Extremely "aggressive" environments such as high external pressures, low temperatures, and chemically active sites represent areas of use of the proposed system. Another application is the use of the proposed system as the power supply for very small satellite systems that may find wider use in the future. The simplicity of the isotope heat source combined with the proposed MRSC convertor will yield high efficiency power supplied with long maintenance free operating lives.

While the radioisotope heat source generally is limited to space applications, the potential also exists that this type of small self contained power source could be used for terrestrial applications. While recovery of the device will be critical, applications such as underwater environmental monitoring in deep-sea areas or under ice in cold climates represents strong possibilities. In these cases the power supply would be directly coupled with the sensor package forming a compact self-contained unit.

The advent of MEMS level combustion devices may also provide a long life, combustion driven heat source that could supply the necessary thermal energy for the low power MRSC system described in the proposed work. These combustors could be based on "conventional" combustion techniques yielding source temperatures well above those provided by the LWRHU configuration or utilize less conventional techniques such as low temperature catalytic reactions providing source temperatures in line with those of the LWRHU system. Application for such devices could include environmental monitoring, metering of remote / dangerous facilities (for example gas / oil wells) where non-conventional combustion techniques may have a premium and a wide range of self powered industrial and consumer products.