General Purpose Heat Source - Exploded view with english labels

The general-purpose heat source is a U.S. DOE-designed radioactive heat source for

radioisotope thermoelectric generator A radioisotope thermoelectric generator (RTG, RITEG), sometimes referred to as a radioisotope power system (RPS), is a type of nuclear battery that uses an array of thermocouples to convert the heat released by the decay of a suitable radioacti ...

s (RTG) or

Stirling radioisotope generator Radioisotope power systems (RPS) are an enabling technology for challenging solar system exploration missions by NASA to destinations where solar energy is weak or intermittent, or where environmental conditions such as dust can limit the ability of ...

s (SRG). It is meant for space applications and is packaged as a stackable module.

Characteristics

GPHSs are fueled with

plutonium-238 Plutonium-238 (238Pu or Pu-238) is a fissile, radioactive isotope of plutonium that has a half-life of 87.7 years. Plutonium-238 is a very powerful alpha emitter; as alpha particles are easily blocked, this makes the plutonium-238 isotope suita ...

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.

Safety

GPHSs are designed with safety in mind and employ

iridium Iridium is a chemical element with the symbol Ir and atomic number 77. A very hard, brittle, silvery-white transition metal of the platinum group, it is considered the second-densest naturally occurring metal (after osmium) with a density of ...

-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.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

Uses

GPHSs of this, or very similar, design were used in the GPHS-RTGs of Cassini-Huygens, New Horizons, the

Galileo probe ''Galileo'' was an American robotic space probe that studied the planet Jupiter and its moons, as well as the asteroids Gaspra and Ida. Named after the Italian astronomer Galileo Galilei, it consisted of an orbiter and an entry probe. It was ...

, and the

Ulysses probe ''Ulysses'' ( , ) was a robotic space probe whose primary mission was to orbit the Sun and study it at all latitudes. It was launched in 1990 and made three "fast latitude scans" of the Sun in 1994/1995, 2000/2001, and 2007/2008. In addition ...

. They are used in the multi-mission radioisotope thermoelectric generator, as used by

Mars Science Laboratory Mars Science Laboratory (MSL) is a robotic space probe mission to Mars launched by NASA on November 26, 2011, which successfully landed ''Curiosity'', a Mars rover, in Gale Crater on August 6, 2012. The overall objectives include investigati ...

(Curiosity rover). They are also used in the advanced Stirling radioisotope generator.

Stages of assembly

File:Radioisotope thermoelectric generator plutonium pellet.jpg, Plutonium pellet. File:Iridium clad GPHS pellet.jpg, Plutonium pellet within iridium cladding. File:Fueling of the MSL MMRTG 002.jpg, Assembled graphite impact shell. File:Fueling of the MSL MMRTG 001.jpg, Assembled module.

References

Department of Energy (DOE) Office of Nuclear Energy GPHS article

"Radioisotope thermoelectric generators (RTGs)" NASA Galileo Information {{refend

External links

NASA Radioisotope Power Systems website – GPHS overview
Nuclear power in space