Can MMRTG Operate on the Moon? Insights from SNAP-27 for Apollo Lunar Surface Experiment Package

The SNAP-27 (Systems Nuclear Auxiliary Power) was a radioisotope thermoelectric generator (RTG) designed and developed to operate in the adverse lunar surface environment for periods of greater than one year, and considered by some to be the pathfinder for what would become the modern RTG program. This RTG provided approximately 70 watts of electrical power to the Apollo Lunar Surface Experiment Package (ALSEP) during both lunar day and night conditions. The first SNAP-27 became operational on the moon in November, 1969, during Apollo 12. SNAP-27s also flew on all of the subsequent Apollo missions, and each unit that was deployed on the moon operated for five to eight years until the ALSEP stations were shut down. While the SNAP-27 performance was not as remarkable as later RTG designs (e.g. the marquee Voyager missions), it is important to note that all of the deployed units exceeded their one/two-year design lifetimes. Impressive by today's standards, the development of the SNAP-27 was initiated only 53-months before the launch of Apollo 12. Review of the available literature from General Electric (GE), NASA, and the Atomic Energy Commission (AEC) reveals that a very extensive design, development, and testing program was conducted prior to the launch of Apollo 12. Ground testing comprised of couple-, module-, and system-level testing to characterize the behavior of the unit to the rigors of the anticipated lunar environment. Over 50 years after those historic missions, the SNAP-27 program much like the science data returned from the ALSEP stations still has something to teach us. As NASA continues to plan for sustained lunar exploration, key capabilities will be identified and developed to establish the first long-term foothold on the lunar frontier. This paper identifies lessons that can be applied from the SNAP-27 program to address the technical challenges/risks to employing current (e.g. MMRTG) and future RTG systems on the lunar surface.