Q: What color is a spaceship?

A: Black and white and (infra)red all over.

Several answers and comments on Why were Europe's first few satellites so stylish? Why the pronounced alternating white and black stripes? contain phrases like "thermal control".

This is back before fancy materials could have both high thermal infrared emissivity and high visible light albedo at the same time. (see answers to Why are RTGs different colors?)

But I can't see why the alternating high/low and low/high ($\epsilon/a$) stripes would be better than just slapping on a coat of gray paint. Did they simply not have gray "space paint" back then and so the stripes were a work-around? Or were there some thermal or other spaceflight or testing advantages that stripes had over a a solid gray?

$\epsilon_{ir}/a_{vis}$ would be thermal infrared emissivity and visible light albedo pairs, not meant to be as a simple ratio though. For an equation using these search this site for "spherical cow temperature".

Shamelessly cropped from images in this question and answer(s):

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On other satellites, such as Explorer 3, reflecting oxide stripes maintain the average inside temperature between reasonable limits; 30 and 100 degrees Fahrenheit.

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    $\begingroup$ I don't think I can make a useful answer to this question. Things have changed significantly in the last half century or so and the requirements on spacecraft coatings have become more complex. What I have done is add a paragraph about the new coating issues to my answer to the original question. $\endgroup$ – Vince 49 Mar 5 at 5:09
  • $\begingroup$ @Vince49 thanks! Ya I think this is different-enough of a question that it should be asked here separately. $\endgroup$ – uhoh Mar 5 at 6:50
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    $\begingroup$ Pure speculation, so not an answer, but: What if I have one paint that's less emissive than I need, and one that's more, and for some reason mixing them to get the emissivity I need won't work. Similarly, maybe I have the uncoated surface and one paint, but the same issue: One is more emissive than I need, and one is less. An actual answer along these lines would explain why the two paints couldn't be mixed, for example. I wish I knew, great question. $\endgroup$ – Wayne Conrad Mar 5 at 19:12
  • $\begingroup$ @WayneConrad now we're talking! The equilibrium temperature equation that I approximated here is too simple. It doesn't take into account 1) that only the sunlit side receives sunlight but both sides radiate and 2) the object will go into eclipse sometime when it will also only radiate, and perhaps those speeds and duty cycles are important. $\endgroup$ – uhoh Mar 5 at 20:07
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    $\begingroup$ Even if mixing them does get that intermediate emissivity, I can imagine it's easier to tweak emissivity during testing by adding more patches of white or black as needed, rather than having to remix a new batch of grey with a slightly different composition. $\endgroup$ – Anton Hengst Jun 24 at 2:25

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