Small Business Innovation Research/Small Business Tech Transfer
High-Efficiency Thermionic Power Generator, Phase II
Project Description
Planetary missions (e.g., Pioneer, Cassini, or Voyager) and applications with moderate power draw and increased mobility requirements (e.g., Curiosity) have successfully employed radioisotope thermoelectric generators (RTGs) as thermal-to-electric power converters. While ~100 We-class radioisotope power sources continue to be in demand, new higher power electric generators (≥500 We) will enable, and enhance, numerous robotic space applications and are ideally suited for upcoming Discovery- through Flagship-class missions. These ≥500 We generators will require both increased source power and increased conversion efficiencies. State-of-the-art thermoelectric generators, for instance, achieve ~7% efficiency, and recent laboratory results are paving a route toward ~15% efficiency. Alternatively, promising results from Lee et al1 and other groups have shown that thermionic thermal-to-electric (TTEC) generators are capable of achieving high conversion efficiency (>25%) at temperatures ≥1200°C by leveraging modern microfabrication techniques. An additional benefit is that the high-quality 'waste heat' from these thermionic systems is rejected at ~800°C, which opens the door to its use as a topping stage for more traditional converters, including thermoelectrics, dramatically raising the ceiling on total system conversion efficiency. To further advance NASA's high-power solid-state thermal-to-electric conversion capabilities, Nanohmics Inc., working in collaboration with The Boeing Company (Huntington Beach, CA) and Sandia National Labs' Center for Integrated Nanotechnologies (CINT) proposes to demonstrate a high-efficiency thermionic thermal-to-electric converter (TTEC) module based on nanostructured, high survivability emission materials. TTEC realization will open up new opportunities for deep space planetary science missions, and future manned spaceflight voyages that are no longer tethered to the sun by photovoltaics.
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Anticipated Benefits
Nanohmics Inc. is developing a novel high efficiency Thermionic Thermal-to-Electric Converter (TTEC) product that uses innovative nanostructured low-work-function emitters capable of high current thermionic electron emission. The primary NASA application of this innovation is for space craft power systems. Within NASA, two key potential customers are the Radioisotope Power Systems (RPS) program and the Evolvable Mars Campaign (EMC). The target application of the TTEC are high power (500 We class or greater) power systems, and specifically RPSs. RPS systems such as Radioisotope Thermoelectric Generators (RTGs) would benefit greatly if the TTEC technology is proven to have higher efficiency and low power degradation rates. Currently, RTGs are used by NASA for deep space missions where solar cell power systems are not practical. If the TTEC can be demonstrated to operate at the same temperature and efficiency as the thermoelectric devices used in RTGs, it has the potential of being a better choice for radioisotope power generation systems on future spacecraft. At the higher end of power generation requirements such as manned mission in the ~ 2025-2030 timeframe, thermionics may reduce Mars round-trip mission times from two to three years, to less than one year. A high temperature thermionic device could be used to help realize this goal using fission energy as the power source. In addition to NASA space power systems, The TTEC could be used as a novel power system for future U.S. Navy and the U.S. Air Force hypersonic vehicles. Additionally, two key markets that present large commercial opportunities are microwave vacuum electronics, and combined cycle power generation. Combined power systems, sometime referred to as combined heat and power (CHP), can generate electricity from the waste heat not used when burning fossil fuels to generate electricity. There is significant interest in developing new thermionics technologies for combined cycle and CHP because of the opportunity to greatly improve the efficiency of these systems. The combined power systems and CHP markets provide a considerable emerging commercial opportunity and is predicted to reach $3.5 billion by 2019 and grow at a considerable rate (CAGR of 20.2%) as by 50% of the U.S. power production is expected to come from natural gas-fired combined cycle plants by 2038. Likewise, microwave vacuum electronics continue to be used for high power radars, radio, and other applications across the military, medical, and space exploration communications. There are over 200,000 vacuum electronic devices used by the DoD alone, and the Navy expects them to be used in radar and electronic warfare systems for many decades to come. Because of their continued use within DoD and other areas, the market for these devices was estimated to be greater than $1 billion for 2015.
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Primary U.S. Work Locations and Key Partners
| Organizations Performing Work | Role | Type | Location |
|---|---|---|---|
| Nanohmics, Inc. | Lead Organization | Industry | Austin, Texas |
| Jet Propulsion Laboratory (JPL) | Supporting Organization | FFRDC/UARC | Pasadena, California |
Primary U.S. Work Locations
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California
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Texas
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