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Comment by WalterBright | Hacker News Reader

Just paint the satellites black?

Yes https://physicsworld.com/a/dark-coated-starlink-satellites-a...

Can't tell if you're joking or not, but SpaceX has indeed been collaborating with astronomical observatories to reduce the apparent magnitude (brightness) to ground for Starlink satellites. It's not as if the potential issues weren't apparent and reported on pretty early on, ie, [0] in summer 2020 before the network entered beta. It's not perfect and the period during orbit raising before the satellites enter operational orbits is more challenging, but very significant reductions have been achieved per recs, see for example "Starlink Gen 2 Mini Satellites Photometric Characterization" [1] in 2023 and "The Brightness of Starlink Mini Satellites During Orbit-Raising" [2] in 2024:

>When magnitudes are adjusted to a uniform distance of 1000 km the means are 4.58 and 7.52, respectively. The difference of 2.94 between distance-adjusted magnitudes above and below threshold implies that mitigation is 93% effective in reducing the brightness of orbit-raising spacecraft.

So there has been progress, though more may be possible particularly as Starship gives them more mass to work with for less money. That may bring new possibilities to spend mass on "cosmetic" purposes to shade and further reduce magnitude even if it contributes nothing to the core functionality. Same as more mass may allow regulators to feasibly require higher levels of redundancy and more margin for deorbiting in case of issues or at EOL.

Of course, that does leave older unmitigated working sats contributing to light pollution for the rest of their operational lifetimes, though worth noting that one of many major advantages for low-LEO/VLEO operation is that by design such lifetimes are much shorter, and in turn generation refresh will happen more quickly. Perhaps more importantly long term, there aren't as far as I know any actual international standards and agreements towards responsible brightness mitigation (or other issues like disposing of expended upper stages responsibly, standardized end-of-life deorbiting, etc). SpaceX has, for both PR and simple corporate self-interest reasons, been a pretty good actor so far even if they get a lot of attention for being the leading first mega constellation. But I really hope follow on efforts from other players can hit the ground running with magnitude reductions at least as good, and that SpaceX itself continues to improve (or at a bare minimum not backslide).

High bandwidth fully global comms is simply too valuable a capability to really imagine going back at this point. But that's no reason not to pursue reasonable compromise mitigations, and potentially some sort of funds to ultimately create far more orbital telescopes as well as part of the package taking full advantage of what upcoming cheap megalift will make possible.

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0: "Impact of Satellite Constellations on Optical Astronomy and Recommendations Toward Mitigations" | https://aas.org/sites/default/files/2020-08/SATCON1-Report.p...

1: https://arxiv.org/pdf/2306.06657

2: https://arxiv.org/pdf/2405.12007

> Can't tell if you're joking or not

Not. Often obvious simple solutions are overlooked. For example, NASA spent huge sums of money trying to design a gas gauge that will work in weightless conditions. Until an engineer suggested just having a "reserve" tank that has enough to bring the spacecraft out of orbit.

Another one was NASA spend a lot of money trying to figure out how to not have the Apollo capsule overheat from the sun. The trivial solution was to make it a rotisserie, i.e. slowly rotate it.

>Not. Often obvious simple solutions are overlooked.

I'm not sure I'd say "often" has something like what you offered up been overlooked by SpaceX. We're long, long past the early eras when everything was first getting figured out, and the timescales and costs are totally different. Talking of "obvious", painting something black in orbit has clear enormous thermal implications, and there are aspects of the system that seem necessarily reflective as well (solar panels, optical links and so on) and in turn mitigation requires cascading design decisions. These aren't platinum plated Apollo era programs either. Like, gut check here: do you see ANY space stations or satellites in space, at all, where they "just painted them black"? I don't think it's actually trivial at all.

Anyway main point is yes, it's recognized and yes, it's getting worked on (successfully!), and I hope that will ultimately help pave the road for any other future megaconstellation efforts by showing what's possible.

I've been designing things my entire professional life, and yes, engineers overlook the obvious all the time (me too!).

I always look for simpler ways, and often enough find them.

It's not just optical pollution, the same satellites visible in the article photo over the Pinnacles are leaking radio spectrum noise into the ostensibly "Radio Quiet Zone" of the nearby Murchison that's home to cosmic microwave sensors and one regional part of the developing global SKA radio telescope platform.

This would be real simple to prove, Starlink Satelites downlink on the same band as Satelite TV so you can use the receiver from a dish that downconverts it to something a cheap dongle can handle and put that all inside a grounded, metal box in the bed of a diesel and just record spectrum.

I was under the impression that actual space business people had ways of not leaking RF when flying over.

It's been proven by several teams already, eg:

  In new research accepted for publication in Astronomy and Astrophysics Letters, we discovered Starlink satellites are also “leaking” radio signals that interfere with radio astronomy. Even in a “radio quiet zone” in outback Western Australia, we found the satellite emissions were far brighter than any natural source in the sky.

from: https://theconversation.com/starlink-satellites-are-leaking-...

referencing: Detection of intended and unintended emissions from Starlink satellites in the SKA-Low frequency range, at the SKA-Low site, with an SKA-Low station analog (Sep. 2023)

https://arxiv.org/abs/2309.15672

It's an ongoing issue in that Starlink v1.0 leaked and as I recall promises were made that the next generation of satellites would leak less and turn off when over radio quiet zones .. that second gen group have (IIRC) more noise and continuing transmitting over RQZ's.

> Although this IEMR abides by ITU-R guidelines, these intensities are large compared to the strongest astronomical radio sources in the sky and will therefore have the potential to disrupt astronomical observations at SKA-Low frequencies;

Sounds like the ITU-R messed up, regardless of why. starlink is 28% of the EIRP the ITU specified. And the "newer generation are a factor of 12 fainter".

We're talking micro. watts. of Effective Isotropic Radiating Power. with 0dBi antennas (unity gain).

I don't understand why they're using those oddball frequencies, but i haven't paid attention to band allocations in a long time. 159.4MHz is Land Mobile band plan - "business band 2 meters", and oh, 137.5 is "SPACE OPERATIONS". I almost want to guess that the 159.4 is a spur of something down around 39.9MHz, fourth harmonic or something. I don't see anything that would let starlink radiate there, unless they change frequencies over countries. Furthermore, it doesn't seem like the 159.4MHz signals will be a detriment to the facility in question, but merely possibly impinge on radio-astronomers.

I understand that these arrays are so sensitive that the RF they collect and process in the career of a scientist there is roughly equal to a cricket chirping once. or something. But microwatts are real tiny, too. Should be possible to put a notch filter at 137.5, or request space businesspeople to do intra-satellite on some other frequency.|

in fact, business idea: aim a yagi array where the satellites are as they pass over, can be done programmatically, or reactively - at least 4 sensors however far from the facility monitor the starlink downlink frequencies (not 137.5 and 159.4, but the ku band ones) - and then aim at the satellite.

I'll build it out with crap i have in my shed to prove it works if anyone is interested. If you know a satellite is in your second of sky, and you monitor, specifically, the 137.5 frequency with a separate, real sensitive antenna array, you can just drop the IQ/whatever from the radios for that timeframe.

This isn't rocket science, QRM and QRN will plague us forever. Thanks, Marconi.

That would seem to remediate one problem, but they still block the view of cameras and telescopes - worse, in a way, that they might block the view without the viewer realizing they missed the occulded star.

Even better, paint it vantablack

https://en.wikipedia.org/wiki/Vantablack

It should also be possible to de-orbit obsolete satellites faster if they can at end-of-life deploy a "sail" that will cause more drag.

Eddy-current-generating tethers seem a more practical option:

<https://www.colorado.edu/faculty/kantha/sites/default/files/...>

(A plot point in Neal Stephenson's Seveneves.)

And then we have to consider what’s the effect of all those vapourised metals on the atmosphere

Probably not much. There’s already an estimated 48 tons of material falling into the atmosphere every day.

https://science.nasa.gov/solar-system/meteors-meteorites/fac...

Might then have a lot of overheating satellites :)

Put the black surface an inch away from the satellite, supported by standoffs. That'll keep the heat away from the satellite.

Also, the black surface only needs to be on the Earth facing side.

It isn't that simple, is it? Even if you place the black surface on a spacer (adding mass, might I add), the black surface itself is going to radiate heat back onto the satellite via blackbody radiation. This is always going to create a worse thermal situation unless you can somehow radiate away as much heat as you could with reflections. To see what I mean, check out JWST's thermal shield.

To complicate it further I thought that some of the military sats had rotating black panels to shield them from ground visibility?

It's likely that military satellites used a bunch of tricks to hide itself. But I don't know how useful they are these days. All major space powers have radars powerful enough to easily pick them out. They're needed for satellite collision avoidance analysis.

Consider a shaped charge. It seems wild to me that you can direct an explosion with various shapes of the explosive. Perhaps a similar idea can apply to the blackbody radiation - get it to radiate mostly away from the satellite.

Also, the black part will be pointed at the Earth, not the Sun.

Not sure what geometry you're thinking of. Whatever idea it is, you're stuck dealing with Kirchoff's law, which says optical emissivity and absorptivity are the same number at any given wavelength. I.e., you can't create "one-way trap doors" for heat flow—that would be a Maxwell's demon. Stacking multiple surfaces isn't a way to circumvent this.

If it's just an asymmetric shape, with different material surfaces pointed in different directions, than that of course is permitted.

https://en.wikipedia.org/wiki/Kirchhoff%27s_law_of_thermal_r...

Kirchoff's law doesn't say which direction it emits in. As shaped charges can alter the direction of where the blast wave goes, I suspect an analogous behavior of a heat shield can direct where the emissions go. I.e. as you say, an asymmetric shape.

PS I haven't done thermo in nearly 50 years!

V-groove radiators are a really neat, unintuitive design, which gets strong directionality out of thermal radiation. It's the thermal design SPHEREX went with—the space telescope that went up a few weeks ago, that was all over HN.

That's: a cavity that's a thin wedge in between two slightly angled plates, where the interior surface coating is partly emissive, and partly infrared-reflective—it can reflect the thermal radiation it emits. That means specular reflections, following geometric optics, so it works like a horn for light—beams it out the sides in a narrow cone.

(.pdf) https://ttu-ir.tdl.org/server/api/core/bitstreams/71aee1e9-3...

How about something like this?

  |              __
  |        |_/\_|  |
  |        | \/ |__|
  E        1  2   3

E is the Earth. 1 is a thin lightweight black disc to block the view of the rest of the satellite. 3 is the working parts of the satellite. 2 are mirrors to direct any emissions from 1 in the direction of 3 out to the sides and to direct any emissions from 3 in the direction of 1 out to sides.

You should check the JWST thermal shield. It addresses exactly this problem. Also keep in mind the additional cost it incurs.

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