“Next Generation Radioisotope Thermoelectric Generators and Reproduction of Cassini-Era SiGe“
Radioisotope thermoelectrics generators have been used to power NASA space missions since 1960s. The Voyager 1 & 2 spacecrafts launched 1977 are now outside the solar system and still sending back signals to earth. SiGe alloys have been used to convert heat from Pu-238 based General Purpose Heat Source (GPHS) to electric power until the Cassini (1997) and New Horizon (2006) missions. PbTe/TAGS thermoelectrics are used in multi-mission RTG and currently powering the Curiosity rover which landed on Mars in 2021.
As NASA planned its future missions, the requirements for more power and up to 17 years lifetime initiated a program, Next Generation RTG, in 2019. New thermoelectric materials that can operate at temperatures up to 1000ºC have been considered including zintl phase compounds, LaTe and nano-bulk SiGe. Specific requirements on technology readiness level (TRL) and timetable for missions in 2030s resulted in a decision to reproduce the Cassini-era SiGe and GPHS RTGs with 300-400W beginning of life power. ORNL is producing Pu-238 fuels for the GPHS and taking on a task to make SiGe using the induction vacuum melting and casting. Materials properties of SiGe and specific microstructures of the heritage SiGe will be presented. SiGe phase diagram is used to explain why the heritage SiGe made from vacuum casting has better performance than the “advanced” versions of nano-bulk SiGe produced by mechanical alloying. Materials-related issues beyond small scale-laboratory research will be highlighted.
Hsin Wang received his BS degree of Solid-State Physics from Tsinghua University in 1989 and his MS and Ph.D. in Ceramic Science from the New York State College of Ceramics at Alfred University in 1991 and 1994. He joined Oak Ridge National Laboratory in 1995 and is currently a distinguished scientist at the Materials Science and Technology Division. His research focuses are on transport properties of materials, advanced thermal imaging, thermal management and reliability of Li-ion energy storage systems, effect of neutron irradiation on material properties.
Dr. Wang was the president of the International Thermal Conductivity Conference (ITCC) and is a current member of ITCC board of directors. He was the host of the International Thermoelectric Conference (ICT) in 2014 and a board member of ICT from 2012 to 2019. He was the Thermoelectric Materials Annex leader of the International Energy Agency (IEA) from 2010 to 2020. He is current a member of the NASA NextGen team and ORNL task leader of the SiGe Task Force.