Mission of Daring: The General-Purpose Heat Source Radioisotope Thermoelectric Generator

The general-purpose heat source radioisotope thermoelectric generator (GPHS-RTG), which was most recently flown on the New Horizons mission to Pluto, was originally conceived in 1979 and executed in a crash program to replace another RTG for the planned International Solar Polar Mission (ISPM). ISPM would later morph into the Ulysses mission to explore the polar regions of the Sun. When the benefits of the GPHS-RTG technology became apparent, the Galileo program also adopted the GPHS-RTG as the power source for orbital exploration of Jupiter. The GPHS-RTG then became the power source of choice for the Cassini mission to Saturn. The GPHS-RTG was designed such that it could produce 300 We at fueling with a mass of 55.9 kg, making the GPHS-RTG the most powerful RTG with the highest specific power ever flown.