I know many cruise missiles use star navigation, I wonder if satellites have any effect on that, and if they do that might be the catalyst to reduce that pollution.
There’s a funny amount of beef around using it in art, you have Anish Kapoor who bought exclusive rights to use Vantablack artistically and man of the people Stuart Semple offering his versions Black 1.0, 2.0, 3.0, 4.0 getting ever blacker.
The entire underside of these satellites is a big phased array antenna. Maybe you can paint it so it absorbs all the other wavelengths, but it would be counterproductive to absorb the radio wavelengths used by the antenna itself since ground emitters would have to increase the gain to get through it.
As someone in this field, I don't really think this is a good idea. We already have issues maintaining proper thermals without turning the satellite into a giant light-absorbing thermal mass. Painting it black is just asking for additional thermal management budget and mass additions.
The blackbody equilibrium temperature at 1AU from the sun is about 278K. All satellite materials are fine at 278K because that's within the expected range of storage and atmospheric launch temperatures.
The equilibrium temperature of a polished aluminum surface at 1AU from the sun is 416K, hot enough to melt polyethylene and at least weaken many of the relevant aerospace plastics like the PET in mylar film.
Painting polished aluminum black drastically raises emissivity along with the lowered reflectivity, and brings its behavior closer to a blackbody.
So does allowing aluminum to oxidize, which it does almost instantaneously in atmosphere. So it's not like it's going to change anything drastically.
The reason this seems like it should change things a lot is that you're used to convectively cooled matte surfaces on Earth, where emissivity and radiative cooling is a less relevant factor and the only significant effect of painting something black is primarily that it absorbs more energy.
How does this happen? Why would something which reflects light on the outside get hotter than one which absorbs light? This makes no intuitive sense to me.
The radiative equilibrium temperature is a function of (watts in - watts out), with a fourth power law shoved in there somewhere. A blackbody at radiative equilibrium absorbs whatever visible light you throw at it, and then spits it back out according to a distribution law that mostly places it in the thermal infrared bands (at temperatures we've familiar with, anyway).
Remove convection/conduction as heat transfer methods, and you end up with two numbers dictating radiative balance:
Percent reflectivity in the bands it's exposed to
Percent emissivity in the bands it's emitting
The balance between these dictates temperature, and they're generally inversely correlated. Mirrors are good reflectors, but very poor emitters.
"The blackbody equilibrium temperature at 1AU from the sun is about 278K. All satellite materials are fine at 278K because that's within the expected range of storage and atmospheric launch temperatures."
But that is NOT the temperature of something in LEO. You're ignoring everything else that adds energy to the system. Friction from collisions with atomic oxygen, down to heating up to temperatures as hot as 530 Kelvin just entirely dependent upon orientation to the sun.
My impression is that friction is negligible once firmly in LEO. Orientation of a sub-component surface definitely matters, as does Earth's presence in half of the viewshed. But my point is that surface finish also makes a big deal, and paint is not necessarily a bad thing, because of the emissivity increases.
(Though I'd rather anodize the thing black imperfectly if it helps avoid paint flecks becoming orbital debris)
True, but I think that could cause issues for astronomers. Instead if seeing small points of light they could see fast moving black spots obscuring stellar objects. In a way looking like eclipses.
So? Intermittent, short-termed blockages happen (jets and satellites already do this, they just aren't black).
Astronomers don't look first and then aim their cameras, and most interesting features (essentially all of them) require long exposures, which would make this problem a slight, one-time variance in brightness.
https://youtu.be/N9VaJKIO1JA?si=UI36apNYUe5mlxWd
The equilibrium temperature of a polished aluminum surface at 1AU from the sun is 416K, hot enough to melt polyethylene and at least weaken many of the relevant aerospace plastics like the PET in mylar film.
Painting polished aluminum black drastically raises emissivity along with the lowered reflectivity, and brings its behavior closer to a blackbody.
So does allowing aluminum to oxidize, which it does almost instantaneously in atmosphere. So it's not like it's going to change anything drastically.
The reason this seems like it should change things a lot is that you're used to convectively cooled matte surfaces on Earth, where emissivity and radiative cooling is a less relevant factor and the only significant effect of painting something black is primarily that it absorbs more energy.
Remove convection/conduction as heat transfer methods, and you end up with two numbers dictating radiative balance:
Percent reflectivity in the bands it's exposed to
Percent emissivity in the bands it's emitting
The balance between these dictates temperature, and they're generally inversely correlated. Mirrors are good reflectors, but very poor emitters.
But that is NOT the temperature of something in LEO. You're ignoring everything else that adds energy to the system. Friction from collisions with atomic oxygen, down to heating up to temperatures as hot as 530 Kelvin just entirely dependent upon orientation to the sun.
(Though I'd rather anodize the thing black imperfectly if it helps avoid paint flecks becoming orbital debris)
I'm not sure making space debris invisible to visible light is a good thing, either.
Visual isn't the only concern, either. https://observatoiredeparis.psl.eu/starlink-satellites-a-thr...
Astronomers don't look first and then aim their cameras, and most interesting features (essentially all of them) require long exposures, which would make this problem a slight, one-time variance in brightness.
>Dr Noelia Noel, Senior Lecturer, PhD in Astrophysics
Is this a joke article?