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How bad are satellite megaconstellations for astronomy?

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Re: How bad are satellite megaconstellations for astronomy?

#121

Post by StellarScience »

schiffern wrote: post #112
malfist wrote: post #99

Earlier quoted context omitted.

Where do you see that the full well of those CCDs are fully saturated by a single satellite streak? Even if that was the case, that seems a very poor design for a sensor and not really an issue of satellites. If a satellite streak can saturate your well, then so could a decently dense star field. Do they blow out the individual pixels? Sure. But you just stack. You don't lose sensitivity just because your stack rejec…

It's not really that it saturates the entire image, it's that bright objects creates non-linear and ghosting artifacts which degrade the sensitivity of the entire exposure, even after post-processing in software. https://www.space.com/bluewalker-3-prototype-satellite-brigh... https://www.nature.com/articles/s41586-023-06672-7 https://iopscience.iop.org/article/10.3847/1538-3881/abba3e/...

Thanks for providing all those links. Indeed, the key there is peak magnitude. BlueWalker 3 has a giant array that reflects light like a mirror. So when you happen to get the angle of incidence exactly equal to the angle of reflection, it shines quite brightly. Of course since it's reflecting all sunlight in one direction, that means from all other spots on earth it will be extremely dim.

Also note that BlueWalker 3, like most low-earth orbit satellites, is only visible during "terminator conditions", when the satellite itself is illuminated by the sun but the telescope is still in darkness. Those times are typically an hour or so after sundown or an hour or so before sunrise. So one solution is to schedule astronomy for the middle of the night, when none of these low earth satellites will lit by the sun at all. Which certainly increases the costs of astronomy, since you can't use your telescope for as many hours per day.

Or, just use your space object catalog to look elsewhere in the sky when bright satellites happen to be in the sky during terminator illumination conditions. Which I see is one of the things your last link, "Mitigation of LEO Satellite Brightness and Trail Effects on the Rubin Observatory LSST", suggests!

Re: How bad are satellite megaconstellations for astronomy?

#122

Post by jacobolus »

hedora wrote: post #118
rgmerk wrote: post #111

Earlier quoted context omitted.

Growing up in a small town, I could see thousands of stars on a clear night. In a major metropolitan area where I live now, it’s hundreds. When I visited Beijing for three weeks, I think there was one night where the pollution cleared sufficiently to see any stars at all; I think I saw three or four.

LED’s are causing an exponential ramp in lighting pollution right now. (They’re more efficient, so people install them in more places and leave them on longer.) Legislation is probably the only way to fix it.

People are convinced that their towns are "safer" if the lighting is bright enough to read a newspaper in the middle of every street in the middle of the night by street lamp alone, and think their oversized SUV seems tougher if the headlamps sear the eyeballs of everyone else on the road.

For actually necessary amounts of outdoor lighting at nighttime, LEDs are not any more power efficient than low-pressure sodium lamps, and considering how bright LEDs are often made, total power consumption is significantly higher.

The lighting industry has absolutely zero respect for human ergonomics, and is happy to sell as much new lighting as they can as often as they can with marketing spin built on pseudo-scientific nonsense. Surely there must be some engineers in the industry with basic understanding of human vision, but they aren't calling the shots. Policymakers are happy to channel Federal subsidies and local tax revenue through to the lighting industry, tossing out PR announcements about how "green" and "modern" they are being along the way.

Re: How bad are satellite megaconstellations for astronomy?

#124

Post by jryle70 »

bmitc wrote: post #107
ggreer wrote: post #100

Earlier quoted context omitted.

What environmental impact? So far there have been 162 Starlink launches. Each launch uses around 200 tons of RP-1, which is equivalent to the fuel capacity of a Boeing 747. In other words: A single 747 burns more fuel in a year than all the Starlink launches in the past five years.

Rocket launches are far more environmentally non-friendly than planes. You can't just look at fuel capacity. It's the composition and where the waste product gets dumped. Rockets dump their waste much higher up in parts of the atmosphere much more sensitive to it. Comparing a rocket and plane isn't an effective comparison in terms of environment impact. So this: > A single 747 burns more fuel in a year than all the S…

> is not an accurate summary of the environmental impact of rocket launches.

So what is the accurate summary of the environmental impact of rocket launches? 10 times more than B747? 100 times? How would it look compared to aviation?

> rocket launches are incredibly disruptive to the local ecosystems of the launch sites.

Not according to FAA when they issued license for SpaceX's launches at KSC - [0]

[0] - https://www.faa.gov/sites/faa.gov/files/space/environmental/...

Re: How bad are satellite megaconstellations for astronomy?

#125

Post by schiffern »

StellarScience wrote: post #121
schiffern wrote: post #112

Earlier quoted context omitted.

It's not really that it saturates the entire image, it's that bright objects creates non-linear and ghosting artifacts which degrade the sensitivity of the entire exposure, even after post-processing in software. https://www.space.com/bluewalker-3-prototype-satellite-brigh... https://www.nature.com/articles/s41586-023-06672-7 https://iopscience.iop.org/article/10.3847/1538-3881/abba3e/...

Thanks for providing all those links. Indeed, the key there is peak magnitude. BlueWalker 3 has a giant array that reflects light like a mirror. So when you happen to get the angle of incidence exactly equal to the angle of reflection, it shines quite brightly. Of course since it's reflecting all sunlight in one direction, that means from all other spots on earth it will be extremely dim. Also note that BlueWalker 3,…

The BlueWalker 3 antenna is white, not mirrored. It will reflect sunlight like a lambertian reflector, not like a specular reflector as you suggest.

https://ast-science.com/wp-content/uploads/2022/07/2022-03-1...

SpaceX has offered their space-rated mirror technology at cost to other satellite manufacturers, but it seems AST SpaceMobile hasn't taken them up on the offer. I can't see any mirrored surfaces on BlueWalker 3.

  >that means from all other spots on earth it will be extremely dim
The second paper I linked (see Figure 1) shows a minimum magnitude after array deployment of 5.5 magnitude, from multiple observatories at multiple locations on the Earth. That's still 10 times brighter than the IAU limit.

  >just look elsewhere in the sky
The hottest thing right now is whole-sky surveys like Vera Rubin (which are important because they can alert other telescopes to transient events), which can't really do that because they're already looking at... the whole sky.

Re: How bad are satellite megaconstellations for astronomy?

#126

Post by ooterness »

martinky24 wrote: post #123
FredPret wrote: post #46

It'd be so cool if we can put up a huge antenna / scope on the far side of the moon. You'd be completely shielded from all human noise

Doesn’t the moon rotate

No. The moon is tidally locked to the Earth, so its rotation exactly matches its orbital period. If you put a telescope on the far side, it'll always be pointing away from Earth.

Re: How bad are satellite megaconstellations for astronomy?

#127

Post by ericcumbee »

bmitc wrote: post #105
hagbard_c wrote: post #63

Earlier quoted context omitted.

If the promises made for new launch systems like SpaceX' Starship (and maybe even, one day, in some unknown future, Bezos' Blue Origin manages to launch something larger than a phallic pond hopper?) it should become radically less expensive to launch larger telescopes into orbit and/or to e.g. the moon.

That "should" needs a lot of backing up, and I don't understand why we need to singlehandedly rely on the same company creating the issues to apparently solve them with wishful thinking.

They are doing the prelim work for a possible service mission to hubble at no cost. I'm sure it won't be entirely free if its executed.

Re: How bad are satellite megaconstellations for astronomy?

#128

Post by briandw »

Mega-constellations also mean that access to space is getting cheeper. Bigger and more plentiful space telescopes should offset the loss from ground based astronomy in the long run. It's no consolation in the near term. But imagine the possibilities for a Starship sized telescope, or many of them.

Re: How bad are satellite megaconstellations for astronomy?

#129

Post by KennyBlanken »

hedora wrote: post #118
rgmerk wrote: post #111

Earlier quoted context omitted.

Growing up in a small town, I could see thousands of stars on a clear night. In a major metropolitan area where I live now, it’s hundreds. When I visited Beijing for three weeks, I think there was one night where the pollution cleared sufficiently to see any stars at all; I think I saw three or four.

LED’s are causing an exponential ramp in lighting pollution right now. (They’re more efficient, so people install them in more places and leave them on longer.) Legislation is probably the only way to fix it.

The issue with LEDs is that they are broad spectrum, whereas sodium lights always fall in a very narrow band in the spectrum which is easily handled with a physical filter.

Re: How bad are satellite megaconstellations for astronomy?

#130

Post by thayne »

StellarScience wrote: post #42

There certainly is a real concern for astronomers, but the photo illustrations used in the article are selected to make things seem worse than they really are. They're wide field of view, long-duration exposures. That used to be the way astronomers imaged space, with film systems a century ago. But these days astronomical telescopes tend to have much narrower fields of view (like tiny soda straws peering into one par…

If you are looking for short period events, losing a single frame can mean losing critical data.

> Or they can just use that information for better scheduling: wait a minute or two to image a particular spot, so there won't be satellites in the field of view.

Which means more time and effort, and ultimately money needs to be spent on scheduling observations to avoid the thousands of these satellites.

And sometimes it isn't an option. What if a GRB happens in the same field of view as one of these satellites and you want to observe it as soon as possible?

Now there are some types of observations that won't be impacted that much. If you can tolerate scheduling around it, or throwing away some of your frames it is just a minor annoyance. But a lot of observations are also more sensitive to such disruptions.

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