NASA seeks novel low power thermal-to-electric miniature energy conversion technology to potentially define the next-generation of future power systems. These converters are required to transform thermal energy from Radioisotope Heater Units into on-demand electricity essential to space exploration probes, unmanned surface rovers, small landers, small satellites, and similar small-scale systems operating in darkness. In response, Creare proposes to develop an extremely compact, robust, free-piston Otto‑cycle based energy conversion system. Our innovation fuses advances in miniature two-stroke engines, and high-reliability free-piston technology. We have achieved a remarkably simple system design with a single moving part, requiring no recuperators or valves. Keys to our high efficiency include reduced parasitic heat losses, the use of a high molecular mass/low thermal conductivity working fluid, tight clearances and high pressure ratios. Our converter leverages decades of advances at Creare in the design and fabrication of miniaturized spaceflight piston-compressors, high-reliability vacuum pumps, and low‑power thermodynamic systems such as turbo-Brayton generators and cryocoolers. In Phase I we will validate our performance models through the development of a laboratory-scale prototype, demonstrating power generation at prototypical heat source and heat sink temperatures. During Phase II we will demonstrate a complete prototype system and prime it for spaceflight testing.
Potential NASA applications for our converter technology include coupling with radioisotope heat sources to support low-power devices such as space exploration probes, unmanned surface rovers, small landers, and small satellite systems operating in darkness. Our converter can be sized to support a wide range of power levels from larger spacecraft applications to smaller more compact electronics required for manned exploration of the lunar and Martian surfaces. Alternative heat sources include concentrated solar radiation.
Terrestrial versions of our converter would be coupled with non-nuclear heat sources such as fossil fuel/biofuel combustion, refuse burning, and concentrated solar energy, to produce electric power for small-scale military and civilian applications. These miniature heat engines are attractive as potential prime movers in Micro-Air Vehicles and as battery replacements in man-portable devices.