What powers a spacecraft in deep space?
The Nimbus III/SNAP-19 launch on April 14, 1969, represented the first flight of a nuclear power supply on a NASA observatory and the culmination of six years of interagency effort between NASA and the AEC. (Atomic Energy Commission)
A plutonium pellet.
Schematic of the RTG
From the earliest days of the Nimbus III/SNAP-19 program the potential aerospace nuclear safety requirement of ejecting the generators from the Nimbus observatory in the event of a launch abort, or a short orbit reentry, impacted the SNAP-19 system design and arrangement on the observatory.
Since 1961, the United States has flown 41 radioisotope thermoelectric generators (RTGs) and one reactor to provide power for 25 space power systems. Thirty-eight of these nuclear power sources on 22 space systems are still in space or on other planetary bodies. To date, US radioisotope thermoelectric generators have successfully operated for over 24 years in space. These RTGs have met or exceeded their prelaunch requirements and in so doing they have greatly expanded humanity’s knowledge of the universe.
Courtesy of IEEE TRANSACTIONS ON GEOSCIENCE ELECTRONICS, VOL. GE-8, NO. 4, OCTOBER 1970
Journeys In Science 