Radioisotope Thermoradiative Cell Power Generator
This NASA Innovative Advanced Concepts (NIAC) project investigates a revolutionary power source for missions to the outer planets utilizing a new paradigm in thermal power conversion, the thermoradiative cell (TRC). Available solar energy decreases as the square of the distance from the Sun, resulting in very low irradiance at the outer planets making photovoltaics infeasible. Instead, current missions beyond Jupiter are powered by radioisotope thermoelectric generators (RTG) which can only convert about 6% of the thermal energy produced by their expensive, and difficult to produce, plutonium heat sources. The TRC is a new alternative in solid state thermal to electrical energy conversion which operates like a solar cell in reverse. Photons are spontaneously generated by recombination of charge carriers inside the TRC diode which are rejected into cold outer space, thus cooling the TRC. A radioisotope heat source maintains the TRC temperature, allowing this radiative emission to drive a current inside the device and provide power to an external load. Low bandgap semiconductor materials are necessary for operation, leading RIT to investigate InAsSb at 0.28 eV. Our work suggests power conversion efficiencies in excess of 12% are possible in this system, doubling that of current state-of-the-art RTGs. Higher power conversion efficiency will enable better utilization of plutonium, and the reduced form factor of the TRC versus the RTG will allow use in many small cubesats as opposed to one large craft, increasing mission capabilities.