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The Multihundred-Watt radioisotope thermoelectric generators (MHW RTG) is a type of US radioisotope thermoelectric generator (RTG) developed for the Voyager spacecraft.
Each RTG had a total weight of 37.7 kg including about 4.5 kg of Pu-238. It uses 24 pressed plutonium-238 oxide spheres and provides enough heat to generate approximately 157 watts of electrical power initially - halving every 87.7 years.
Each RTG generated about 2400 Watts of thermal power. Conversion of the decay heat of the plutonium to electrical power used 312 silicon-germanium (SiGe) thermoelectric couples. The initial thermoelectric couple hot junction temperature was 1273 K (1832 °F) with a cold junction temperature of 573 K (572 °F).
Each Voyager spacecraft has 3 RTGs. Collectively, the RTGs supplied each Voyager spacecraft with 470 watts at launch.
MHW-RTGs were used on the Lincoln Experimental Satellites 8 & 9, and to this day continue to provide power on Voyager 1 and Voyager 2.
Subsequent US spacecraft used the GPHS-RTG which used similar SiGe thermoelectic devices but a different packaging of the fuel. Another later RTG was the MMRTG