Study: ultra-black coating could reduce satellite light pollution | Hacker News Reader

Study: ultra-black coating could reduce satellite light pollution

surrey.ac.uk

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 paint is sold through Semple’s brand, Culture Hustle, and remains explicitly unavailable to Anish Kapoor or his affiliates"

I saw a few of these black Anish Kapoor sculptures. The experience was worth the cost. The brain has a hard time processing it.

Well, you've not actually seen the sculptures per se, only a missing area of the visual background, shaped like outline of the sculptures.

True! One can walk around and then observe some of the shape. They were behind glass. So no touching, which means there was some unresolved ambiguity.

Which is all a dumb marketing stunt because it was never a pigment artists could paint with anyway.

People have made art with the stuff.

I’m not saying otherwise, but look at how it has to be applied to an artwork.

Semple's humorous long-form performance art, pillorying Kapoor, while developing a menagerie of new pigments, is much more interesting than Kapoor's sculptures.

Anyone could have made at least the same with the given material, and a more talented artist could stun, but sadly they are not allowed to because contract.

Tangential, but everyone can take part in reducing light pollution because it's well suited to local political action: https://darksky.org/what-we-do/advancing-responsible-outdoor...

Needs signup to download a form? :/

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.

I think it only needs to be on the Earth side of the satellite?

Correct. This is why SpaceX rejected using black coatings alone for Starlink. Mirrored surfaces that they tested instead were darker than VANTA black.[0]

On some surfaces they use a SpaceX-designed coating called Low Reflectivity Black, which is the least specular space-rated paint by a factor of 5.[1]

[0] https://www.youtube.com/watch?v=MNc5yCYth5E#t=2430s

[1] https://starlink.com/public-files/BrightnessMitigationBestPr...

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.

That's the cost of pollution.

Yes, it's a trade-off between engineering/maintenance costs and public good. As always.

I'm not sure making space debris invisible to visible light is a good thing, either.

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.

Ah right, it reflects in both directions of course. Thanks.

"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)

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.

communication link bandwidths are typically miniscule compared to optical spectrum of the sun

Sure, maybe you can find a paint that is black in all bands except for the ones used by the satellite. It won't use carbon black.

Why is the wording always so hedged? Anything "could reduce" anything, this equivocates so much that it's useless for understanding anything.

That’s just Vanta advertisement

Yup, they wrote the paper.

> "...researchers demonstrate how Vantablack® 310 – an ultra-black coating developed by University of Surrey spinout Surrey NanoSystems, co-authors of the paper..."

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.

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.

Give it few years and they'll get LED colors and we'll see them in "I'm lovin it" formation.

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.

I'm sure they use image stacking to mitigate these issues.

They do, but they're also very openly frustrated already with the proliferation of large satellite constellations.

Visual isn't the only concern, either. https://observatoiredeparis.psl.eu/starlink-satellites-a-thr...

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.

The Darkest Clothing in the World:

https://youtu.be/N9VaJKIO1JA?si=UI36apNYUe5mlxWd

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.

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.

Is it really good idea to make satellites "hidden" from sight? As a general idea it feels like an obstacle should be visible. Not hidden. Camouflaging a cell phone mast as a tree is one thing. Making a sattelite invisible sounds very much like not the same thing

Surely satellite collision avoidance is not based on visual checks?

I would assume it's a combination of globally shared known trajectories plus radar tracking stations.

The floating ring of space debris around Earth would like to have a word with you.

I think you could earn at least a little money back on the development/manufacture of such a product if you found some commercial applications.

Can I get some of that for my target gun sights?

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 are a lot of stars, the probability of obscuring a sufficient number of suitable stars is astronomically small

have radar transparent faceted dome/covers on the earth side, the faceting will reduce light reflectivity in any given direction

and yes there are plenty of radar transparent composites used in aviation and ship domes

Also erase stars.

unless they can make it weightless there will be no incentive to use it for anything to do with space

>Astha Astha, Postgraduate Research Student

>Dr Noelia Noel, Senior Lecturer, PhD in Astrophysics

Is this a joke article?

> Noelia Noel

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)

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