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After reading this answer about the RTGs used on the Lunar surface, I added some of the images from the Wikipdia article Apollo Lunar Surface Experiments Package into this answer, where I noted that the Lunar soil at that location was pretty dark by comparing it to the darkness of the radiator fins of the RTG.

Then I looked up and noticed that the whole side of the LEM appears to have the texture of crinkled metallized film, but it's extremely dark! Is this a result of the landing, or was it supposed to be like that? I thought the purpose of the metallization was to reflect the sunlight to avoid the more than 1 kilowatt of light per square meter from overheating the spacecraft and crew. Did this darkening cause trouble?

I don't recall seeing LEMs so dirty - assuming this is lunar soil, was this darkening site-specific?

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above: Cropped and annotated details from: "Astronaut Alan L. Bean from Apollo 12, put the Plutonium 238Pu Fuel from the Lunar Module into the SNAP 27 RTG" from here. note: red rectangle highlights possible missing "black stuff", blue rectangle highlights a shadow from a sunlit part of the "black stuff." other blue arrows show shadows cast from sunlit rods. Small blue arrows show a dark surface with bright gold circular areas suggesting a pattern of screws or fasteners perhaps.

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above: "Astronaut Alan L. Bean from Apollo 12, put the Plutonium 238Pu Fuel from the Lunar Module into the SNAP 27 RTG" from here

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above: Apollo 11 NASA image 1969-059C appears to be the same side of the LEM, although a different mission. The "dark stuff" is there but surrounded by bright film on either side.

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  • $\begingroup$ @AndrewThompson look closer along the right side of the detail in the cropped image I provided to address this issue directly. I can see small spots where the dark stuff is missing and the bright gold color appears. $\endgroup$ – uhoh Aug 27 '16 at 5:02
  • $\begingroup$ @AndrewThompson I've added two rectangles - one showing a bright spot, the other showing a demonstrably sunlight part - since it's shadow is also apparent to the left. You can see more shadows - from some rods - up near the top of this side panel, in the full image also. $\endgroup$ – uhoh Aug 27 '16 at 5:11
  • $\begingroup$ Related: Why does the ascent stage of Apollo 11's lunar module look like it's made of paper? $\endgroup$ – kim holder Aug 27 '16 at 15:25
  • $\begingroup$ @kimholder yes very very related. I like the title but i wouldn't have clicked on it searching for this - good find. Wow - "hand crinkled"!! $\endgroup$ – uhoh Aug 27 '16 at 15:42
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The black areas are matte black Pyromark-painted Inconel insulation blankets. The parts of the lunar modules that would experience a lot of heating due to the exhaust of the reaction control thrusters had this material as the outer layer of their insulation blankets. There were four sets of thrusters placed 90o apart, each with four thrusters, and they looked like this:

reaction control thrusters on the Apollo lunar module

From the Apollo News Reference Lunar Module Quick Reference Data:

Because the top deck and side panels of the descent stage are subjected to engine exhaust, these areas are extensively protected with a nickel inconel mesh sandwich outboard of the mylar and H-film blankets.

Flat black material both absorbs and emits heat better than any other color material. From The Naked Scientists:

Essentially, when light is absorbed, a photon of light comes in and hits an electron, giving it some energy.

Now whether it’s absorbed or not will depend on the structure of the electrons [in the atom]. If there's somewhere for the electron to go, and if it can increase it's energy level, then it will absorb the light. If not, then the light can't be absorbed and carries straight on. If it is absorbed, the substance looks black. If it isn't, it’s white [because the light is reflected back].

This means that, if you heat something up, if there's [a higher energy level] somewhere for the electrons to go up to, and it’s black, then there's also somewhere for the electron to drop down to again, meaning that the substance will also emit energy.

So if something is good at absorbing light then it’s also good at emitting it. So a black thing should be much better emitting light than a white thing.

The Lunar Module Coatings Page has diagrams showing where all the different kinds of insulation and coatings were used on the lunar landers.

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  • $\begingroup$ OK that makes sense. This is a protective layer of some combination of oxidized inconel and paint. I just added one more photo of what looks to be the same side of the LEM, but this time Apollo 11. Any idea why this area is protected from exhaust, but all the other shiny film on either side doesn't require it? $\endgroup$ – uhoh Aug 27 '16 at 15:12
  • $\begingroup$ @uhoh the areas on either side are angled away from the side with the thrusters and blocked by the struts wrapped in the Inconel. The Inconel protection was heavier so they would have used it as little as possible. $\endgroup$ – kim holder Aug 27 '16 at 15:28
  • $\begingroup$ oh oh oh thrusters! I understand now!!! This stuff! Would you consider adding this or a similar pic to your answer? I kept seeing "thruster" and thinking somehow thrust from the main engine of the lander was somehow reflected back up. I forgot about these things! $\endgroup$ – uhoh Aug 27 '16 at 15:38
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    $\begingroup$ @uhoh Done. At first i said 'rocket engines' instead of thrusters in the answer, and then i fixed it, so your confusion is understandable :P $\endgroup$ – kim holder Aug 27 '16 at 15:51

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