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Comment by pocketstar | Hacker News Reader

a "matte black" spacecraft would get very very hot, too hot for most electronics and be detectable with an IR camera. ion thrusters use significant power and would require a large and visible solar array. misty would be technically possible but a motivated adversary would probably be able to find it. stealth spacecraft are difficult.

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I think you could use black body radiators on the other 5 sides to bleed the heat from the side facing the sun.

those black body radiators(doesnt exist) will be visible in the IR...unless you can get them down to 3K to blend in with the background. Running a spacecraft that cold is pretty impractical because all the bus equipment uses power and any power=heat. Any power generation will be hot, rtg or solar.

they will be IR visible, but what do you mean they don't exist? Apollo used them to bleed off excess heat.

"A black body is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence." [0] Black bodies are theoretical, they do not exist. Apollo had radiators, they might have been black but they were not a black body. Vantablack comes close to a black body for the visible spectrum which is p cool tho.

[0]https://en.wikipedia.org/wiki/Black_body

> Black bodies are theoretical, they do not exist. Apollo had radiators, they might have been black but they were not a black body.

they were, as I said, "black body radiators" which are not theoretically ideal black bodies, but still manage to radiate black body radiation.

I think the term you're looking for is simply "radiator."

yes that is more parsimonious however in non-technical language the term "radiator" is associated with heat exchangers. if you put heat exchangers on the sides of your spacecraft they would function as radiators so I suppose it doesn't matter anyway, arguing semantics is a waste of time.

a "radiator" is a heat exchanger and "radiator" is the industry standard term. these semantics are required for effective communication about technical topics.

There have been black spacecrafts, like the Polyus: https://en.wikipedia.org/wiki/Polyus_(spacecraft)

A majority of the exterior surfaces on spacecraft are black, gold or OSR. The black or gold however is multi layer insulation. Where the outboard surface would get hot and the inboard surface would be cooler. Where the OSR surface is your radiator area. Regardless, all visible in IR.

One could perhaps build a large flat reflector to shield it from the sun's rays and angle it in such a way to not reflect sunlight or radar signals back to earth-based receivers. But I don't know the extent of space radar systems, maybe there are transmitters and receivers spread around widely enough that that would not work.

Like the JWST?

Yes but maybe larger and angle to present an oblique surface to earth based and perhaps orbital radar and telescopes. Although I suspect this world be harder than it sounds due to the number of such radars likely in orbit.

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