page_title: Application of silicon-germanium thermoelectrics in space exploration
section_title: Thermocouple/unicouple assembly
hierarchical_section_title: Application of silicon-germanium thermoelectrics in space exploration / Thermocouple/unicouple assembly
caption_attribution_description: English: The thermoelectric couple (also called thermocouple or unicouple) consists of a SiGe n-leg doped with boron and a SiGe p-leg doped with phosphorus as thermoelements for heat conversion into electrical power in radioisotope thermoelectric generators (RTGs).
context_page_description: Silicon-germanium thermoelectrics have been used for converting heat into power in spacecraft designed for deep-space NASA missions since 1976. This material is used in the radioisotope thermoelectric generators that power Voyager 1, Voyager 2, Galileo, Ulysses, Cassini, and New Horizons spacecraft. SiGe thermoelectric material converts enough radiated heat into electrical power to fully meet the power demands of each spacecraft. The properties of the material and the remaining components of the RTG contribute towards the efficiency of this thermoelectric conversion.
context_section_description: The thermocouples/unicouples attached to the outer shell consist of a SiGe alloy n-leg doped with boron and a SiGe p-leg doped with phosphorus to provide thermoelectric polarity to the couple. The electrical and thermal currents of the system are separated by bonding the SiGe alloy thermocouple to a multifoil cold stack assembly of molybdenum, tungsten, stainless steel, copper, and alumina components. Several layers of Astroquartz silica fiber yarn electrically insulate the legs of the SiGe thermocouples. In between the inner insulation system and the outer shell, copper connectors form the electrical circuit, which uses a two-string, series-parallel wiring design to connect the unicouples.  The circuit loop arrangement minimizes the net magnetic field of the generator.
caption: Conceptual diagram of a thermocouple (unicouple)
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