SNAP-19 Radioisotope Thermoelectric Generator Fact Sheet by Energy Research & Development Administration (ERDA) Page 5

The history of the SNAP-19s includes their first use on NASA Pioneer Jupiter and Pioneer 10 Missions launch in March and December of 1973 and 1973. Even these deployments however were not the same configuration as the internal SNAP-19s customized to address the needs of a surface mission. Viking was the first surface mission to utilize SNAP-19 technology. Current references to RTGs have been made in a recent 2015 film, The Martian.