The SNAP-27 (System for Nuclear Auxiliary Power) was developed for the US. Atomic Energy Commission by General Electric Company for use by the National Aeronautics and Space Administration during the Apollo Lunar Exploration Program. The SNAP-27 is a radioisotope-fueled thermoelectric power generator designed and developed to operate in the adverse lunar surface environment for periods of greater than one year. The generator and fuel deliver in excess of 72 watts through the lunar night and lunar day to power the ALSEP (Apollo Lunar Surface Experiment Package).

The first SNAP-27 ALSEP was put in place on the moon in the Ocean of Storms on November 19, 1969 by Astronauts Alan L. Bean and Charles P. Conrad. This SNAP-27 developmental unit is one of several that were subjected to the rigors of a simulated lunar environment for a period of greater than one year to verify the adequacy of the flight SNAP-27. It was donated to the Smithsonian in 1970.