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> 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://noir

> 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/ 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 upcoming Rubin Observatory) are among the highest-profile ground-based astronomy projects today. 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. Narrow field instruments (such as spectrographs) have less geometric chance of seeing a satellite but tend to take longer exposures (tens of minutes), so there is a greater loss of telescope time when a streak does happen. Even space telescopes are affected by streaks (https://www.space.com/hubble-images-spoiled-starlink-satellite-steaks https://www.space.com/hubble-images-spoiled-starlink-satelli...). > It takes a bit more work and software Equivalently, it takes more money and time. That just means less science, given flat to declining funding from Congress.

nomel 2y ago
> 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 assume that the window is almost always clear, especially for an individual sensor.
- hedora 2y ago
  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.
  - schiffern 2y ago
    >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.
    - labcomputer 2y ago
      So just write all grant proposals with an extra 5% slop.
      - dexwiz 2y ago
        Why would they not already be trying to maximize grant size?
      - schiffern 2y ago
        Budgets are fixed, so again this also boils down to "just do 5% less science." Believe it or not, actually using 100% capacity on the big expensive telescope you paid for isn't some brilliant unheard-of suggestion like people seem to think. This Dunning-Kruger idea always seems to crop up whenever this particular topic is in the news. There simply isn't any "slop in the system" that lets you get that 5% (and climbing!) back "for free." If there was, then that inefficiency should be fixed regardless of the situation with megaconstellations.
        nimish 2y ago
        Doing 5% less science is an acceptable cost for full commercial space exploitation. I'd rather have internet service in 100% of the US than an extra few graduate theses. And who knows, necessity is the mother of invention so one of those grad students could invent a way around it.
        schiffern 2y ago
malfist 2y ago
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 rejected pixels, that's not how stacking works. You wind up with a tiny bit more noise, how much more depends on your capture. But not lower sensitivity, stacking isn't just average an area
- schiffern 2y ago
  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-brightest-objects-sky https://www.space.com/bluewalker-3-prototype-satellite-brigh... https://www.nature.com/articles/s41586-023-06672-7 https://www.nature.com/articles/s41586-023-06672-7 https://iopscience.iop.org/article/10.3847/1538-3881/abba3e/meta https://iopscience.iop.org/article/10.3847/1538-3881/abba3e/...
  - StellarScience 2y ago
    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!

nomel 2y ago

> 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 assume that the window is almost always clear, especially for an individual sensor.

hedora 2y ago
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.
- schiffern 2y ago
  >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.
  - labcomputer 2y ago
    So just write all grant proposals with an extra 5% slop.
    - dexwiz 2y ago
      Why would they not already be trying to maximize grant size?
    - schiffern 2y ago
      Budgets are fixed, so again this also boils down to "just do 5% less science." Believe it or not, actually using 100% capacity on the big expensive telescope you paid for isn't some brilliant unheard-of suggestion like people seem to think. This Dunning-Kruger idea always seems to crop up whenever this particular topic is in the news. There simply isn't any "slop in the system" that lets you get that 5% (and climbing!) back "for free." If there was, then that inefficiency should be fixed regardless of the situation with megaconstellations.
      - nimish 2y ago
        Doing 5% less science is an acceptable cost for full commercial space exploitation. I'd rather have internet service in 100% of the US than an extra few graduate theses. And who knows, necessity is the mother of invention so one of those grad students could invent a way around it.
        schiffern 2y ago

malfist 2y ago

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 rejected pixels, that's not how stacking works. You wind up with a tiny bit more noise, how much more depends on your capture. But not lower sensitivity, stacking isn't just average an area

schiffern 2y ago
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-brightest-objects-sky https://www.space.com/bluewalker-3-prototype-satellite-brigh... https://www.nature.com/articles/s41586-023-06672-7 https://www.nature.com/articles/s41586-023-06672-7 https://iopscience.iop.org/article/10.3847/1538-3881/abba3e/meta https://iopscience.iop.org/article/10.3847/1538-3881/abba3e/...
- StellarScience 2y ago
  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!