General Purpose Heat Source
The General Purpose Heat Source is a U.S. DOE-designed radioactive heat source for Radioisotope Thermoelectric Generators (RTG) or Stirling radioisotope generators (SRG). It is meant for space applications and is packaged as a stackable module.
GPHSs are fueled with plutonium-238 dioxide. Each module has a temperature of over 600 degrees Celsius and delivers 250 watts at the time of manufacture. 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 iridium-clad plutonium-238 dioxide pellets. The generated alpha particles are blocked by the cladding, thus no further radiation shielding is necessary. The pellets are encased within nested layers of carbon-based material and placed within an aeroshell housing to comprise the complete module.
The modules can withstand extreme conditions including a launch-pad explosion or a high-speed reentry. Overheating and impact tests were performed on several sample modules.
GPHSs of this, or very similar, design were used in the GPHS-RTGs of Cassini-Huygens, New Horizons, the Galileo probe, and the Ulysses probe. They are used in the Multi-Mission Radioisotope Thermoelectric Generator, as used by Mars Science Laboratory. They are also used in the Advanced Stirling Radioisotope Generator.
Stages of assembly
- Los Alamos report "General-purpose heat source safety verification test series: SVT-11 through SVT-13". 1986-05-01, OSTI 5664400. doi:10.2172/5664400