Characteristics of Apollo RTGs on the lunar surface

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Contents 1 Requirements 2 Results 2.1 Background 2.2 Apollo 12 2.2.1 RTG Power Output 2.3 Apollo 14 2.3.1 RTG Power Output 2.4 Apollo 15 2.4.1 Positioning 2.4.2 RTG Power Output 2.4.3 Maps 2.4.4 Photos 2.5 Apollo 16 2.5.1 RTG Power Output 2.6 Apollo 17 2.6.1 RTG Power Output 3 Summary and Conclusion

Requirements

This study seeks to uncover as much data as possible of relevance to determining the feasibility of using the radioisotope thermoelectric generators (RTG's) left on the lunar surface by the Apollo missions to heat Team FREDNET's rover during lunar night, including:

1. Accessibility: are there any obstacles in the way that would prevent us getting close?
2. How many RTG's are there at the different landing sites and which ones could be on the Team FREDNET mission plan?
3. How much power can we expect from a particular RTG?
4. How much heat can we expect from a particular RTG?
5. What level of maneuverability / arm extension would the rover need to have to make contact with the RTG?
6. How long will it take to get to the RTG from the lander and get into acceptable position?
7. What other information is available on the RTGs? Is there any photos? In-situ photos? Diagrams?

Results

Background

With the exception of the aborted Apollo 13 mission, radioisotope thermoelectric generators were deployed on the lunar surface by all Apollo missions 12 through 17 as the power supply of each mission's Apollo Lunar Surface Experiment Packages (ALSEP) experiment. Each mission deployed exactly one RTG.

The fuel capsule, containing 3.8 kilograms (8.4 pounds) of plutonium-238 in oxide form (44,500 Ci or 1.65 PBq), was carried to the Moon in a separate Fuel Cask attached to the side of the Lunar Module. The fuel cask provided thermal insulation and added structural support to the fuel capsule. On the Moon, the Lunar Module pilot removed the fuel capsule from the cask and inserted it in the RTG.^[1]

All Apollo RTG's were of the SNAP-27 model and were designed and manufactured by General Electric.

Apollo 12

RTG Power Output

Apollo 14

RTG Power Output

Apollo 15

Positioning

The Apollo 15 RTG was placed approximately 43 meter west (slightly north-west) of the mission's retroreflector array[1].

RTG Power Output

Maps

• Layout of Apollo 15's ALSEP. Planned layout of the Apollo 15 ALSEP package.
• Artist's concept of the Apollo 15 ALSEP layout. The relative positions of the instrument are as planned and close to the deployed configuration.

Photos

• NASA AS15-92-12406 (OF300)
• NASA AS15-92-12409 (OF300)
• NASA AS15-92-12416 (OF300)

Apollo 16

RTG Power Output

Apollo 17

RTG Power Output

Summary and Conclusion

Our original figures underestimated the rate at which the power output of the Apollo RTGs decreased. In all five cases, the power output had dropped from around 70 W to 30 W (approximately 40% of the original output) after less than just 130 lunations, or approximately 10 years. Assuming this tendency continued for approximately 30 more years, the power output would be all but zero today. Hence, it is not possible to derive any useful amount of power directly from the RTGs themselves today.

First posted by Anders Feder 20 November, 2008.