37.7 kg, including about 4.5 kg of Pu-238 and uses 24 pressed plutonium-238 oxide spheres to provide enough heat to generate approximately 157 watts of electrical power initially - halving every 87.7 years.

Each RTG initially generated about 2400 watts of thermal power.Conversion of the decay heat of the plutonium to electrical power uses 312 silicon-germanium(SiGe) thermoelectric