Is there a link to where this topic might be discussed? Obviously the LM was covered in highly reflective Mylar and must have had some insulation, but with that constant Sun, I can see where overheating could be a question. It doesn't seem to be mentioned as an issue in the books I've read over the years.

There was a pretty lengthy discussion about this at the Apollohoax forum several months ago. If you read through the thread I'm sure you'll find some pretty good answers there.

http://www.apollohoax.com/forums/viewtopic.php?t=1428

Here's a good place to start

The descent stage was wrapped in aluminized Mylar. That's Mylar with an extremely thin layer of aluminum sprayed on it. That way you get the optical properties of metal without the weight of metal. The Mylar they used was orange in color, and you attach it with the Mylar side out, so it looks shiny gold. Mylar also has emissive properties that help out the heat-rejection solution. That coating itself is only about 50% reflective in the infrared, if memory serves. It's not necessarily "highly reflective" but it's certainly more reflective than the lunar surface itself -- about 7X as reflective.

The ascent stage was covered in polished aluminum sheets, somewhat more reflective than the Mylar.

The lunar module design was subjected to computerized radiant heat transfer analysis, the forerunner of the complex analysis that's done today using supercomputers. This was used to estimate the solar heat load on the spacecraft and adjust the design accordingly. Aluminum, being far less absorptive than most of the natural minerals on the moon, simply doesn't get as hot as the 200 F horror stories declare.

Insulation is a key concept here. The whole point of insulation is to "insulate" or isolate two adjacent parts so that heat is not transferred between them. This is why the Mylar was crinkly. It was hand-crinkled in order to minimize the contact area between adjacent layers. In the space suits you had alternating layers of materials that did not transfer heat well between them. That means the outer layers of these insulation blankets can indeed reach high temperatures -- 100 F or 150 F or whatever -- while the inner layers remain at a more constant temperature.

The joy of thermal design is realizing that you don't have to keep everything cool. It doesn't matter if a landing strut is 100 F on one side. It will still work.

The problem with insulation is that inhabiting and operating a spacecraft generates heat, and that heat has to be gotten rid of, and the insulation can make that hard. The lunar module incorporated several radiators that rejected heat to space through radiation. That involves nothing more complex than transfering heat to these radiator panels via convection of a refrigerant, and keeping those radiators facing the blackness of space (i.e., away from the sun, sunlit mountains, the lunar surface, etc.).

Some parts of the lunar module (i.e., the bulbous propellant tank housings on either side of the cabin) were actually painted black so that they would absorb more heat than they should have. This is because the fuel inside had to be maintained essentially at room temperature, and the normal absorption through the aluminum and subsequent radiation into the tanking wasn't enough to do that; the fuel was liable to freeze.

So the real heat transfer problem with lunar module was not solar heating. That was managed quite well through fully passive design elements such as coatings and materials. No, the real problem was rejecting the heat generated by the astronauts and by the spacecraft's electronic components. Special radiators had to be made to do that.

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