I was listening to the Plutonium episode of "the Elements" on the BBC, and between 07:00 and 08:30 they talked about uses of plutonium such as spacecraft power and heat. While the returning astronauts in Apollo 13 were not actually "keeping warm" using the RTG, I didn't realize that the spacecraft actually had RTGs.

In this answer I found that indeed the Apollo 13 LEM contained an RTG.

Was it just the one RTG per LEM that was used in Apollo spacecraft, or were there more? Were they just used as a passive, steady source of heat to insure things didn't get too cold, or for a source of power also?


1 Answer 1


The RTGs powered the Apollo Lunar Surface Experiments Package.

This is also the first thing that comes up when you google "Apollo RTG".

  • $\begingroup$ Is that the only use? Only Apollo missions that carried surface experiment packages carried RTGs? They were never parts of the spacecraft themselves? $\endgroup$
    – uhoh
    Commented Aug 27, 2016 at 3:14
  • 2
    $\begingroup$ That is correct. The wikipedia article gives a timeline showing how the RTG fuel elements were not even inserted until the astronauts were on the Lunar surface. $\endgroup$ Commented Aug 27, 2016 at 3:29
  • 2
    $\begingroup$ The From the Earth to the Moon TV miniseries episode on Apollo 13 touches on this. I think the explanation given there is "it's a battery for the lunar surface experiments". $\endgroup$
    – user
    Commented Dec 13, 2016 at 15:00

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