GPHS-RTG

[1] The GPHS-RTG has an overall diameter of 0.422 m and a length of 1.14 m.[1] Each GPHS-RTG has a mass of about 57 kg and generates about 300 watts of electrical power at the start of mission (5.2 We/kg), using about 8.1 kg of Pu-238 which produces about 4,400 watts of thermal power.

As a result, the missions were slightly adapted to utilize the lower power that would be available.

[3] The decay heat reduces by about 0.8% per year, so the thermoelectric converter 'ages' or degrades to some extent.

The thermoelectric elements convert the heat energy from the isotope into electricity.

[4] Missions after 2010 requiring RTGs, such as the Mars Science Laboratory, will use the Multi-Mission Radioisotope Thermoelectric Generators instead.

Diagram of an RTG used on the Cassini probe [ 1 ]
Diagram of a stack of general-purpose heat source modules as used in RTGs
Image of a plutonium RTG pellet glowing red hot .