A conceptual spacecraft radioisotope thermoelectric and heating unit (RTHU)

Abstract

SUMMARY Spacecraft venturing to the outer planets and beyond—or onto the planetary surface where available solar energy is reduced—benefit from the longevity and consistency of electrical and thermal energy derived from radioisotope energy sources. A review of likely mission requirements and concept studies of small electrical generating units (<10 We) reveals a potential opportunity for a unit with an electrical output of around 1 We that can also supply some heat to the spacecraft to aid thermal control: a radioisotope thermoelectric and heating unit. This power requirement cannot be achieved with current US space‐qualified modular radioisotope fuel assemblies. Additionally, new European programmes consider 241Am fuel to be much more cost effective than 238Pu. Taken together, these factors provide the rationale for taking a relatively ‘clean‐sheet’ approach to design of a radioisotope thermoelectric and heating unit fuelled with 241Am. In this paper, initial requirements and performance targets for such a unit are developed, a simple concept design and thermal model is presented and the performance and mass are estimated. The results suggest that units generating 1–2 We may achieve a specific power of around 0.7–0.9 We kg−1 without the thermal inputs to spacecraft becoming impractically large. Such units can use a bismuth telluride thermoelectric material, which is commercially applied in terrestrial applications and is therefore likely to incur lower cost and development risk than more specialised compounds. This study may form the basis of a more detailed design effort. Copyright © 2011 John Wiley & Sons, Ltd.

Planetary Robotic System Design

“…However, such improvements are pending upon appropriate funding support being provided to advance the development of these systems. While the radioisotopic power source have obvious advantages, they also possess some disadvantages that can make the implementation difficult as shown in Table 2 [136,137]. Am 241 being only a 1/4 of the power density of Pu 238 , RTG and RHU systems based on americium will be invariably heavier and bulkier.…”

Spark plasma sintered bismuth telluride-based thermoelectric materials incorporating dispersed boron carbide

“…The Seebeck and resistivity data are presented in Figure 4 with the resulting power factor, showing that 0.1 and 0.2 vol% B 4 C have little deleterious effect on performance for a fixed temperature difference, but addition of 0.5 vol% B 4 C does start to reduce potential power output. Power factor is a sound means of assessing potential power output for a fixed temperature across a thermoelectric, but in RTG applications the temperature difference is not fixed because the system is power-limited [5], so some estimate of zT is better means to evaluate the effect on system performance. Figure 5 shows the thermal conductivity and a comparative zT calculated using the data in Figure 4 and 5(a).…”

“…Systems under development for potential future application in Europe would use americium-241 due to its lower cost [3]. Am-241 has approximately one quarter of the energy density of Pu-238 [3,4], which will lead to lower temperatures and heat flux through the thermoelectric elements; this drives the selection of bismuth telluride thermoelectric materials with high aspect-ratio (long) legs [5]. A key advantage of bismuth telluride based materials is that proven module manufacturing approaches are available, which lowers technical development risk.…”

Enhancement of energy performance in betavoltaic cells by optimizing self-absorption of beta particles

“…Radioisotope battery has received considerable attention for applications requiring long-life electrical power sources in space or under harsh conditions with a need for capable micro size energy sources [1][2][3][4]. Especially, these radioisotope energy sources could be applied to the space mission to outer planets or planetary surface, where the availability of solar energy is reduced [5]. The radioisotope thermoelectric generator (RTG), which converts the decay heat from radioisotopes into electricity, was mainly developed and applied in numerous deep-space missions such as the plutonium RTG that powers the Curiosity rover for recently on-going Mars exploration [6].…”