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Dynamic Power Conversion

Description:

Scope Title:

Dynamic and Solid-State Power Conversion

Scope Description:

NASA is developing thermoelectric and dynamic radioisotope power systems (DRPSs) for unmanned robotic missions to the Moon and other solar system bodies of interest. This technology directly aligns with the Science Mission Directorate (SMD) strategic technology investment plan for space power and energy storage and could be infused into a highly efficient RPS for missions to dark, dusty, or distant destinations where solar power is not practical. Current work in RPS is focused on advanced thermoelectric (TE) materials and dynamic cycle machines, including Stirling and Brayton convertors that would be integrated with one or more 250-Wth general-purpose heat source (GPHS) modules or 1-Wth lightweight radioisotope heater units (LWRHU) to provide high thermal-to-electric efficiency, low mass, long life, and high reliability for planetary spacecraft, landers, and rovers. Heat is transferred from the radioisotope heat source assembly to the power convertor hot end using conductive or radiative coupling. Power convertor hot-end temperatures would generally range from 300 to 500 °C for RHU applications and 500 to 1,000 °C for GPHS applications. Waste heat is removed from the cold end of the power convertor at temperatures ranging from 20 to 175 °C, depending on the application, using conductive coupling to radiator panels. The NASA projects target power systems able to produce a range of electrical power output levels based on the available form factors of space-rated fuel sources. These include a very low range of 0.5 to 2.0 We that would utilize one or more RHU, a moderate range of 40 to 70 We that would utilize a single GPHS Step-2 module, and a high range of 100 to 500 We that would utilize multiple GPHS Step-2 modules. For these power ranges, one or more power convertors could be used to improve overall system reliability. The current solicitation is focused on innovations that enable efficient and robust power conversion systems. Areas of interest include:

  1. Robust, efficient, highly reliable, and long-life thermal-to-electric power convertors that would be used to populate a generator of a prescribed electric power output ranges.
  2. Electronic controllers applicable to Stirling, Brayton, or Rankine power convertors.   
  3. Multilayered metal insulation (MLMI) for minimizing environmental heat losses and maximizing heat transfer from the radioisotope heat source assembly to the power convertor.
  4. Advanced dynamic power conversion components and RPS integration components, including efficient alternators able to survive extended exposure to 200 °C, robust high-temperature-tolerant Stirling regenerators, robust highly effective recuperators, integrated heat pipes, and radiators that improve system performance and improve the margin, reliability, and fault tolerance for existing components.
  5. Advanced solid-state thermal-to-electric power conversion components and RPS integration components, including advanced thermoelectric and thermionic devices that advance performance, reliability, and efficiency; enable long life operation (greater than 20 years); and/or enhance manufacturing processes for materials and components.

Expected TRL or TRL Range at completion of the Project: 2 to 5

Primary Technology Taxonomy:

  • Level 1 03 Aerospace Power and Energy Storage
  • Level 2 03.1 Power Generation and Energy Conservation

Desired Deliverables of Phase I and Phase II:

  • Research
  • Analysis
  • Prototype
  • Hardware

Desired Deliverables Description:

Phase I deliverables: results of feasibility study, modeling, and/or component testing to demonstrate basic feasibility.  

 

Phase II deliverables: prototype hardware that has demonstrated basic functionality in a laboratory environment, the appropriate research and analysis used to develop the hardware, and maturation options for flight designs.

State of the Art and Critical Gaps:

Radioisotope power systems are critical for long-duration NASA missions in dark, dusty, or harsh environments. Thermoelectric systems have been used on the very successful RPSs flown in the past, but are limited in efficiency. Advances in solid-state power conversion components are desired to increase performance, reliability, efficiency, and life for RPSs. Dynamic thermal energy conversion provides significantly higher efficiency, and through implementation of noncontacting moving components, can eliminate wear mechanisms and provide long life. Although high-efficiency performance of dynamic power convertors has been proven, reliable and robust systems tolerant of off-nominal operation are needed. In addition to convertors appropriate for GPHS RPSs, advances in much smaller and lower power dynamic power conversion systems are sought that can utilize RHUs for applications such as distributed sensor systems, small spacecraft, and other systems that take advantage of lower power electronics for the exploration of surface phenomenon on icy moons and other bodies of interest.  Although the power convertor advances are essential, to develop reliable and robust systems for future flight advances in convertor components as well as RPS integration components is also needed. These would include efficient and robust thermoelectric couple configurations, efficient alternators able to survive 200 °C; robust high-temperature-tolerant regenerators; robust high-efficiency recuperators; heat pipes for heat addition or rejection; radiators; and controllers applicable to Stirling flexure-bearing, Stirling gas-bearing, or Brayton convertors.

Relevance / Science Traceability:

This technology directly aligns with the Science Mission Directorate, Planetary Science Division, for space power and energy storage. Investments in more mature technologies through the Radioisotope Power System Program is ongoing. This SBIR subtopic scope provides a lower TRL technology pipeline for advances in this important power capability that improves performance, reliability, and robustness.

 

References:

  • NASA: "Radioisotope Power Systems," https://rps.nasa.gov/about-rps/overview/
  • Oriti, Salvatore: "Dynamic Power Convertor Development for Radioisotope Power Systems at NASA Glenn Research Center," AIAA Propulsion and Energy 2018, AIAA 2018-4498.
  • Wilson, Scott D.: "NASA Low Power Stirling Convertor for Small Landers, Probes, and Rovers Operating in Darkness," AIAA Propulsion and Energy 2018, AIAA 2018-4499.
  • Wong, Wayne: "Advanced Stirling Convertor (ASC) Technology Maturation," AIAA Propulsion and Energy 2015, AIAA 2015-3806.
  • Fleurial, Jean-Pierre, Bux, Sabah, and Caillat, Thierry: "Engineering of Novel Thermoelectric Materials and Devices for Next Generation, Long Life, 20% Efficient Space Power Systems," IECEC 2013, AIAA 2013-3927.

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