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How bad are satellite megaconstellations for astronomy?

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Re: How bad are satellite megaconstellations for astronomy?

#111

Post by rgmerk »

pfdietz wrote: post #53
stouset wrote: post #18

Earlier quoted context omitted.

Megaconstellations are not a problem for kids looking through telescopes. If anything it’s additional things to wonder at in amazement.

Indeed. The big obstacle for kids is when the entire sky is washed out with sodium vapor light and maybe you can see Vega.

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.

Re: How bad are satellite megaconstellations for astronomy?

#112

Post by schiffern »

malfist wrote: post #99
gammarator wrote: post #67

Earlier quoted context omitted.

> They're wide field of view, long-duration exposures. That used to be the way astronomers imaged space, Sorry, but one of the two example images ( https://noirlab.edu/public/images/iotw1946a/ ) is a single 333-second exposure with a modern survey camera, the Dark Energy Camera. This is not particularly long nor does it represent some outmoded observational strategy. Large, wide-field imaging sky surveys (such as the…

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/...

Re: How bad are satellite megaconstellations for astronomy?

#114

Post by hedora »

nomel wrote: post #98
gammarator wrote: post #67

Earlier quoted context omitted.

> They're wide field of view, long-duration exposures. That used to be the way astronomers imaged space, Sorry, but one of the two example images ( https://noirlab.edu/public/images/iotw1946a/ ) is a single 333-second exposure with a modern survey camera, the Dark Energy Camera. This is not particularly long nor does it represent some outmoded observational strategy. Large, wide-field imaging sky surveys (such as the…

> Masking and stacking can mitigate the problem but it does not of course compensate for the lost area and sensitivity. And the brightest satellites (like BlueWalker) saturate the readout electronics and spoil the whole exposure. Is this only a problem in systems that aren't aware of where the satellites will be? I naively assume that, if the system knew, it could start exposing in the next clear window. I naively as…

Even if they don’t know where the satellites will be, a simple motion detection algorithm in the stacker would delete the streak caused by the satellite. A given pixel will only be impacted for a few exposures, so just grab 5% more images.

I’d guess terrestrial light pollution is a much bigger problem.

Re: How bad are satellite megaconstellations for astronomy?

#115

Post by martinky24 »

bythreads wrote: post #113

I always thought spacex should stick a 5 dollar webcam to each sattelite pointing upwards and create the worlds largest telescope to just shut everybody up

Can you expand on how sticking a $5 webcam on each starlink satellite would quell concerns?

I’m in the astronomy community and I can’t quite figure it out. If you could expand on what you’re thinking and some of the science behind it, that’d be great.

Re: How bad are satellite megaconstellations for astronomy?

#116

Post by rblatz »

nullc wrote: post #102
malfist wrote: post #97

Earlier quoted context omitted.

Seriously, any time you have >3 images to stack satellites and planes are a complete non issue. The median pixel value is always going to exclude those. Five images is enough to eliminate any trails even if they overlap between images.

You're not imaging with cryogenic CCDs --- satellite trail can blow out whole rows.

Just do it in space and avoid the whole atmosphere and ground based light pollution. Space is cheaper than ever now, this is a problem for amateur astronomers, and hobbyists shouldn’t hold back progress.

Re: How bad are satellite megaconstellations for astronomy?

#117

Post by schiffern »

hedora wrote: post #114
nomel wrote: post #98

Earlier quoted context omitted.

> Masking and stacking can mitigate the problem but it does not of course compensate for the lost area and sensitivity. And the brightest satellites (like BlueWalker) saturate the readout electronics and spoil the whole exposure. Is this only a problem in systems that aren't aware of where the satellites will be? I naively assume that, if the system knew, it could start exposing in the next clear window. I naively as…

Even if they don’t know where the satellites will be, a simple motion detection algorithm in the stacker would delete the streak caused by the satellite. A given pixel will only be impacted for a few exposures, so just grab 5% more images. I’d guess terrestrial light pollution is a much bigger problem.

  >so just grab 5% more images.
You say it like major observatory telescopes are sitting idle, but they're not. In practice what actually happens is you lose 5% of your scientific data return.

  >terrestrial light pollution
Problem is that it's global vs local, so our normal solution for terrestrial light pollution (build telescopes in a remotely populated area) doesn't work.

Re: How bad are satellite megaconstellations for astronomy?

#118

Post by hedora »

rgmerk wrote: post #111
pfdietz wrote: post #53

Earlier quoted context omitted.

Indeed. The big obstacle for kids is when the entire sky is washed out with sodium vapor light and maybe you can see Vega.

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.

Re: How bad are satellite megaconstellations for astronomy?

#119

Post by jacobolus »

pfdietz wrote: post #53
stouset wrote: post #18

Earlier quoted context omitted.

Megaconstellations are not a problem for kids looking through telescopes. If anything it’s additional things to wonder at in amazement.

Indeed. The big obstacle for kids is when the entire sky is washed out with sodium vapor light and maybe you can see Vega.

Dim orange low-pressure sodium lamps are much much better than bright blue–white LEDs.

Re: How bad are satellite megaconstellations for astronomy?

#120

Post by willy_k »

pfdietz wrote: post #91
TeMPOraL wrote: post #87

Earlier quoted context omitted.

Doesn't matter. The point is that, thanks to reusable boosters, launching satellite constellations, and other recent developments, space is becoming much cheaper - so if you can't fit 8 JWSTs in one Starship, just launch the rest on another, and it'll still come out cheaper than the original JWST.

Ultimately it becomes so cheap we'll be able to put workers up there to assemble and maintain the telescopes, just like on Earth. We might see telescopes in telescope farms near a small station for the workers. It might even be possible to send workers out to the Sun-Earth L2 point to maintain telescopes there.

For what it’s worth, people have already fixed telescopes in space (ISS astronauts operating on Hubble).
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