Application of silicon-germanium thermoelectrics in space exploration

Heavily doped semiconductors, such as silicon-germanium (SiGe) thermoelectric couples (also called thermocouples or unicouples), are used in space exploration.

[3][4][5] SiGe alloy devices are mechanically rugged and can withstand severe shock and vibration due to its high tensile strength (i.e. >7000 psi) and low dislocation density.

The multifoil cold stack assembly, composed of molybdenum, tungsten, stainless steel, copper, and alumina materials, provides the insulation between the electrical and thermal currents of the system.

[3][9] A large array of SiGe thermocouples/unicouples form a thermopile that was incorporated into the design of radioisotope thermoelectric generators (RTGs) used in the missions Voyager, Galileo, Ulysses, Cassini, and New Horizons.

[6][11] 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.

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.

[citation needed] The GPHS-RTG employs identical heat-to-electrical conversion technology used in the MHW-RTGs from the Voyager missions, using SiGe thermocouples/unicouples and the Pu-238–fueled GPHS.

[3] Missions after 2010 requiring RTGs will instead use the multi-mission radioisotope thermoelectric generator (MMRTG) containing lead telluride (PbTe) thermocouples and Pu-238 dioxide for spacecraft power applications.