The General Purpose Heat Source
is a stackable, compact unit designed to deliver over 600 degrees Celsius to a Radioisotope Thermoelectric Generator
(RTG) or a Stirling Radioisotope Generator
(SRG), generating 250 watts per unit at the beginning of a mission when used with an RTG, unknown with an SRG. These units are designed to supply heat consistently and safely over a wide range of extreme conditions. They measure 9.948 cm wide x 9.32 cm deep x 5.82 cm high and weigh no more than 1.44 kg each.
GPHSs are designed with safety in mind and employ Plutonium
-238 pellets encased in iridium
to generate alpha particles which are completely absorbed in the heat source to produce heat; thus, no special radiation shielding is necessary to absorb these particles. The resulting iridium-clad plutonium pellets are encased within nested layers of carbon-based material and placed within an aeroshell housing to comprise the complete GPHS-module.
- Department of Energy (DOE) Office of Nuclear Energy GPHS article
- "Radioisotope Thermoelectric Generators (RTGs)" NASA Galileo Information