3 ms·

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 fo

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 3y 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 3y 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!
  - schiffern 3y ago
    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/2022/07/2022-03-18-BlueWalker-3-BW3-array-Microns-1024x737.jpg 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.
  - DiogenesKynikos 3y ago
    > 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. Let me translate that a bit: "So one solution is to just eliminate 20% of all available observing time."
    - malfist 3y ago
      Not really. Astronomical dusk and dawn are different than civil dusk or dawn, you'd normally skip an hour or so after sunset and before sunrise anyway.

schiffern 3y 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 3y 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!
- schiffern 3y ago
  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/2022/07/2022-03-18-BlueWalker-3-BW3-array-Microns-1024x737.jpg 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.
- DiogenesKynikos 3y ago
  > 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. Let me translate that a bit: "So one solution is to just eliminate 20% of all available observing time."
  - malfist 3y ago
    Not really. Astronomical dusk and dawn are different than civil dusk or dawn, you'd normally skip an hour or so after sunset and before sunrise anyway.