colour of radiators

[sralica]

Hey,

I have a question about radiators and radiators in space. what colour should radiators be?

Was reading this, but I am to dumb to understand.

On ISS are white, on shuttle are silver/teflon.

So when we will have mod with radiators, what should the colour be? different for space planes and something else for space stations?

[Brotoro]

I would think radiators should be dark when viewed at infrared wavelengths (to be efficient radiators of heat), while being a light as possible at visible wavelengths (to absorb as little sunlight as possible).

[Ralathon]

That article explains it quite well. The idea is that the radiators are reflective in the visible spectrum while opaque in the infrared spectrum.

The color only matters for the wavelengths the radiator is emitting. So it doesn't really matter for the radiation efficiency what color your paint them in the visible spectrum, since they'll never get so hot that they'll start to glow. Since they're still exposed to visible light from the sun and the earth you might as well paint them white or metallic so they reflect as much as possible. Else you have to deal with that energy in addition to the heat you're trying to radiate away.

This means that the color of the radiator depends on how much heat it is designed to radiate. So normal every day radiators should be colored white. But radiators for high energy applications (Like in the interstellar mod, or the near future mod) should be blueish. That way they'll radiate efficiently in red wavelengths while reflecting incoming blue radiation.

Edited May 1, 2015 by Ralathon

[Shpaget]

I would think radiators should be dark when viewed at infrared wavelengths (to be efficient radiators of heat), while being a light as possible at visible wavelengths (to absorb as little sunlight as possible).

This, but since we are seeing the world aound us in visible, and not IR, my suggestion would be mirror finish in visible light. They would look awesome - almost invisible - black on black with only stars (and nearby bodies) reflecting in them.

[softweir]

That would work if there are any mirror-finish materials available that are sufficiently black-radiative at IR frequencies. Still - it would look neat!

[Jovus]

Depends on the luminosity function for the star you're most likely to be around. For Kerbol I'd expect the most efficient color to be reddish-yellowish-offwhite, since it's probably cooler than our star. But I might be wrong; maybe it radiates primarily in the microwave or something.

[K^2]

That would work if there are any mirror-finish materials available that are sufficiently black-radiative at IR frequencies.

Sure. Actuall mirrors, for example. Glass is opaque in IR.

The problem is that glass is also a pretty poor heat conductor. The surface exposed to space would cool off, but it wouldn't conduct heat off the metal frame all that great. I suspect, real space radiators are made out of aluminum and are coated with a paint that is not entirely unlike thermal paste in composition to give them IR opaqueness without restricting the heat flow. That would be consistent with white or silvery appearance as well.

Ultimately, what you are looking for is not a gloss finish, however, but an albedo. As close to 100% of visible light should be reflected as possible. But direction you reflect it into is irrelevant. You can have light scattered evenly in all directions, and that will make finish look snow-white. You can have tiny clusters with fine finish which will reflect lighti n random directions. That will make it look silvery-gray. Or you can go with fine gloss finish, which will make it look like a mirror. Either way works, but the first two are far more practical to implement, so that's what you see in space.