Thermionic generation for powering hypersonic vehicles

We propose to adapt our existing thermionic devices to integrate directly into hypersonic vehicles. Thermionic energy conversion has the potential to leapfrog competing technologies but has largely been neglected for decades. Today, we have demonstrated best-in-class thermionic performance using novel materials and manufacturing techniques, as well as fully encapsulated prototypes. We have identified waste heat recovery in hypersonic vehicles as a critical application that takes full advantage of this highly power dense and high temperature technology. Our primary focus as part of this Phase I award is to meet stakeholders and decision makers within the Air Force to understand the missions and platforms in which our solution is most compelling, with the goal of identifying pilot demonstration projects as part of a potential Phase II. If successful, our solution will add virtually no extra weight or volume, with the potential to become the “APU” of choice for all next-generation and long-duration hypersonic vehicles. In a thermionic energy converter, electrons evaporate from a hot electrode, the emitter, into a vacuum gap and are collected by a cooler electrode, the collector, to generate electric current. In the 1960- 1970s, multiple groups reported thermionic converters with power densities >10 W/cm2, conversion efficiencies of ~10-15%, and lifetimes over 5 years. However most of this progress was tied to the US space-nuclear program which ended in 1973; thermionics has never fully shaken the perception of being “tried before”. Spark is revitalizing this nascent technology to increase power density and efficiency >2x beyond these historical limits by combining new materials and fabrication techniques stemming from its founder’s PhD at Stanford University. We propose a targeted Phase I effort around defining the details and specifications for the missions and platforms where applying our unique technology to provide power in hypersonic vehicles would create the most immediate value.