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.
One problem with trying to make satellites invisible is that you are making them invisible. Probably the dynamics up there are not the same as down here, or try to apply logic that doesn't work in that environment, but with secret, or failing, broken into pieces, with fried electronics or whatever satellites you may be losing an important hint that something is there.
I noticed the word “heat” is not mentioned anywhere in the article. Considering this reflects 2% of the incident light and absorbs 98% of the sunlight, I would expect the cubesat to get very hot very quickly.
It’s been a while since I last engineered something where thermals were a consideration, but this just doesn’t feel right.
Sounds like what my eye doc says when he busts the laser out for medical work on my eye. His work creates blank spots in my FOV. Not noticeable at all walking around, but they make detail vision difficult. Everything from artistic project work to seeing the center dot on screen in a shooter, and it makes refractory vision checks to figure out my Rx near impossible. The letters in the eyechart just disappear unless can catch them peripherally.
Making blank spots in the sky between the observer and the observed is something I suspect won't really be an improvement. It likely to make the problem less noticable (eg. no more b-roll of streaks in the sky to upset people) and, probably, more of a challenge to mitigate.
I don't think this is comparable. One is generally taking long-time exposures for astronomy pictures (hence the streaks).
So if the satellite is simply blocking light, in the worst case, it will block the light of a star, maybe for a few milliseconds(?) dimming the star in the final picture by a minuscule amount.
This might still be problematic (influencing spectroscopy? dimming the star slightly, influencing some measurements there?) but probably still better than potentially mixing in light from a difference source (?)
astronomy today point to a small piece in the sky to measure some binary star that is barely one pixel on the sensor. now you covered it with a black satellite right when then unique event was about to happen... did it not happen or was hidden by a new satellite?
also, black coating is old news. very old news. and musk said he didn't consider for starlink because he doesn't have to pay for something that doesn't make money directly for himself. so this whole discussion is pointless.
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.
Thats really cool. He did a fine job sewing. I tried something similar with green-screen fabric and followed the same procedure: make a pattern from existing clothing, cut out the material, and sew it up. It's very hard.
> "...researchers demonstrate how Vantablack® 310 – an ultra-black coating developed by University of Surrey spinout Surrey NanoSystems, co-authors of the paper..."
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.
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.
They (SpaceX) added Geofencing to the arrays so that they switch off when over radio telescopes. How well that's working now (I notice that article is a couple of years old) is up for debate.
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.
She is from Argentina. Both are common given names and family names here. Neither is in the top 10 list, but they are not unusual to cause surprise. I'd recommend to avoid using both together to avoid nasty online comments.
> Astha Astha
She is from India. Astha is a common given name there. It looks like it's common in some areas to have only a given name and no family name. I guess in some form she was had to fill a family name and decided to repeat the given name instead of using NULL.
It’s been a while since I last engineered something where thermals were a consideration, but this just doesn’t feel right.
Making blank spots in the sky between the observer and the observed is something I suspect won't really be an improvement. It likely to make the problem less noticable (eg. no more b-roll of streaks in the sky to upset people) and, probably, more of a challenge to mitigate.
So if the satellite is simply blocking light, in the worst case, it will block the light of a star, maybe for a few milliseconds(?) dimming the star in the final picture by a minuscule amount.
This might still be problematic (influencing spectroscopy? dimming the star slightly, influencing some measurements there?) but probably still better than potentially mixing in light from a difference source (?)
also, black coating is old news. very old news. and musk said he didn't consider for starlink because he doesn't have to pay for something that doesn't make money directly for himself. so this whole discussion is pointless.
https://youtu.be/N9VaJKIO1JA?si=UI36apNYUe5mlxWd
> "...researchers demonstrate how Vantablack® 310 – an ultra-black coating developed by University of Surrey spinout Surrey NanoSystems, co-authors of the paper..."
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.
Can I get some of that for my target gun sights?
>Dr Noelia Noel, Senior Lecturer, PhD in Astrophysics
Is this a joke article?
She is from Argentina. Both are common given names and family names here. Neither is in the top 10 list, but they are not unusual to cause surprise. I'd recommend to avoid using both together to avoid nasty online comments.
> Astha Astha
She is from India. Astha is a common given name there. It looks like it's common in some areas to have only a given name and no family name. I guess in some form she was had to fill a family name and decided to repeat the given name instead of using NULL.
Link to the classic article by patio11: "Falsehoods Programmers Believe About Names" (2010) https://www.kalzumeus.com/2010/06/17/falsehoods-programmers-... (a few HN discussions, in particular https://news.ycombinator.com/item?id=21492464 | 150 points | Nov 2019 | 144 comments)