Impacts of Large Satellite Constellations on Astronomy

[ZChris13]

-snip-

Promising!

[thirtyone]

So when I started doing satellite hunting in the sky, a few things hit me. Optically, you can only really see satellites objects in the beginning and end of the night. Note that a lot of the visible objects are actually old rocket boosters, space junk, and other random components - not even actual, proper satellites. There's also already a ton of them flying across the sky (but I would imagine the number would go up a decent amount after more megaconstellation launches).

So is there any concern from satellites *occluding* the sky for measurements or is it just interference from bright objects? For the majority of the night, satellites can't interfere due to brightness - they are only visible at the beginning and end of the night, while at least *some part* of the night sky can see satellites that reflect sunlight.

So the upper bound for lost measurements is probably something like 20-30%? If you take into account sky area, etc. and the fact that they're small object occluding a much larger area, I could totally believe that 1% lost observation number. Is that a reasonable amount of data loss?

Unless of course occlusion is a big problem. I'd be really interested to hear more about that.

[pochimax]

We need a professional study of the real impact.

I think we can't t talk of an homogeneous impact. A 1% loss is not relevant, in my opinion. But it might be some observations (for example, wide angle, all sky, etc)  are more affected than traditional telescopes.

And, again, we need to take into account future ground based capabilities, at least the reasonable expected ones.

[envy887]

We need a professional study of the real impact.

I think we can't t talk of an homogeneous impact. A 1% loss is not relevant, in my opinion. But it might be some observations (for example, wide angle, all sky, etc)  are more affected than traditional telescopes.

And, again, we need to take into account future ground based capabilities, at least the reasonable expected ones.

Agreed that this needs some studies, they need to quantify on the actual data loss and evaluate the cost of mitigations on both sides.

Hopefully the telecons SpaceX is having are helping towards these evaluations.

[mrhuggy]

I'm not totally up with orbital mechanics, disclaimer out of the way.

How about timing and spacing the orbits so there's a window. All orbits have precession so by crafting all  of the orbits you could make it so the satellites miss the telescope making a window for the telescope to work in.

[Mark K]

I'm not totally up with orbital mechanics, disclaimer out of the way.

How about timing and spacing the orbits so there's a window. All orbits have precession so by crafting all  of the orbits you could make it so the satellites miss the telescope making a window for the telescope to work in.

That won't work - a telescope isn't fixed. It can point at different parts of the sky. If you have no orbits visible to the telescope you have the area around the telescope with no Starlink coverage.

[gmbnz]

How about timing and spacing the orbits so there's a window. All orbits have precession so by crafting all  of the orbits you could make it so the satellites miss the telescope making a window for the telescope to work in.

If there are no satellites visible overhead then there's no internet - which somewhat defeats the purpose of starlink

[pochimax]

How about timing and spacing the orbits so there's a window. All orbits have precession so by crafting all  of the orbits you could make it so the satellites miss the telescope making a window for the telescope to work in.

If there are no satellites visible overhead then there's no internet - which somewhat defeats the purpose of starlink

I hope radio astronomy sky sites will be avoided, even if they get no satellite internet. Some kind of "space reservoirs"

[pochimax]

So, the problem with future large FOV telescopes are not bright.

https://www.aura-astronomy.org/news/aura-statement-on-the-starlink-constellation-of-satellites/

One facility, the Large Synoptic Survey Telescope (LSST) under construction in Chile and managed by AURA under a cooperative agreement with NSF, is slated to begin wide-field imaging of the sky in 2022. LSST will create a color motion picture of the universe, and for the first time humanity will view the optical universe with a panoramic view in space and time. However, just as LSST is nearing completion, the dark sky may be partially obscured by bright low Earth-orbiting satellites.

The LSST Project Science Team has been simulating the potential impacts to LSST observations. Their latest update of preliminary results from November 2019 indicates that (assuming the full deployment of planned satellites) nearly every exposure within two hours of sunset or sunrise would have a satellite streak. During summer months there could be a 40% impact on twilight observing time (less in winter) and saturation of sensors by the satellites can continue well past astronomical twilight. Because of scattered light in the optics by the bright satellites, the scientific usefulness of an entire exposure can sometimes be negated. Detection of near-Earth asteroids, normally surveyed for during twilight, would be particularly impacted. Dark energy surveys are also sensitive to the satellites because of streaks caused in the images. Avoiding saturation of streaks is vital. The LSST team notes that “For the full Starlink constellation, at any one time during the night over 200 Low Earth Orbit (LEO) satellites will be visible. This will increase by the mid-2020s with additional planned constellations of LEO satellites.”

The impact of the satellite constellations on other ground-based telescopes that have wide fields, long exposures, and/or less sophisticated data processing pipelines may be as significant as the impact on LSST.

So the impact could be serious.

[eeergo]

Concerning back-of-the-envelope estimates - here's an actual accurate simulation of visible satellites if the full 12k constellation was up in their operational orbits. The absurd sky dominance is considering worst-case illumination conditions in the summer - of course that's also when best weather is available for observations. And this is for *just* the baseline Starlink, in visible wavelengths and not accounting for under-maintenance sats (lower orbits). It is left as an exercise to the reader to add a few competing such constellations, such as the 5 already in the works (totaling approximately as many birds as a 12k Starlink).





More complete blog post with naked-eye visibility and detailed effects on an observation target here (although again under simplifying assumptions of no reflections, no under-maintenance birds): http://www.deepskywatch.com/Articles/Starlink-sky-simulation.html


As a metaphoric aside (i.e. let's not get into arguments about this), the treatment of this issue reminds me of mainstream, layman's discourse about climate change:
- first the whole concept that there is an issue is preposterous,
- then the *concept* is valid, but unconcerning in practice,
- then the effect is actually sound, but there's an overlying cooling trend (!), so all's good,
- then there might actually be a warming, but it's natural,
- then there might actually be some anthropogenic contribution, but negligible,
- then there might be an important anthropogenic contribution, but climate is unpredictable (!)
- then you can actually *see* an effect, but hey look cold waves have continued or even intensified, or something,
- then all that fits into a predictable major manmade contribution, but... plants like heat! and somewhere it will rain more! Plus with the current economy it costs too much to change, do you want famine?
All concerning effects that were known for more than a century, and accurately modeled for 70 years.

[mrhuggy]

How about timing and spacing the orbits so there's a window. All orbits have precession so by crafting all  of the orbits you could make it so the satellites miss the telescope making a window for the telescope to work in.

If there are no satellites visible overhead then there's no internet - which somewhat defeats the purpose of starlink

I hope radio astronomy sky sites will be avoided, even if they get no satellite internet. Some kind of "space reservoirs"

Radio Astronomy does get reserved space already. There are bands that satilities are not supposed to transmit in due to radio astronomy. There's another debate with radio astronomy and 5g bands.

Sent from my Pixel 3a using Tapatalk

[Semmel]

I want to provide some context for the numbers in the last posts.

There are about 17000 space debries objects in the sky that are tracked. These are all tracked because they are visible. The tracking telescopes are small compared to the big astronomical telescopes, so that number is probably not the upper limit for astronomical observations. Any pixel or spectrum that any of these objects touch is garbage. And it is dealt with in data reduction pipelines. Additional 5000 or even 12000 satellited dont even make this worse by a factor of 2.

Cosmic rays are an effect that happens to long exposures high up in the atmosphere. All astronomical instruments are subject to cosmic rays. I have brought you some, see the appendix. This is a small section of a detector image from the MUSE instrument, working on one of the ESO VLTs on Paranal. The image is a dark image (closed shutter) with an exposure time of 1 hour. These things are there all the time. They are the reason why you never take only one frame of an object, always at least 2.

The point I am making: There are plenty of effects that need to be handled. Astronomy will not be over due to Starlink et al. The true impact has to be calculated by a very careful analysis that take everything else into account. If anyone finds a paper, please tell me!

[eeergo]

I want to provide some context for the numbers in the last posts.

There are about 17000 space debries objects in the sky that are tracked. These are all tracked because they are visible. The tracking telescopes are small compared to the big astronomical telescopes, so that number is probably not the upper limit for astronomical observations. Any pixel or spectrum that any of these objects touch is garbage. And it is dealt with in data reduction pipelines. Additional 5000 or even 12000 satellited dont even make this worse by a factor of 2.

Cosmic rays are an effect that happens to long exposures high up in the atmosphere. All astronomical instruments are subject to cosmic rays. I have brought you some, see the appendix. This is a small section of a detector image from the MUSE instrument, working on one of the ESO VLTs on Paranal. The image is a dark image (closed shutter) with an exposure time of 1 hour. These things are there all the time. They are the reason why you never take only one frame of an object, always at least 2.

The point I am making: There are plenty of effects that need to be handled. Astronomy will not be over due to Starlink et al. The true impact has to be calculated by a very careful analysis that take everything else into account. If anyone finds a paper, please tell me!

Nope, the number of catalogued objects in orbit is >19000, and several thousands more are tracked but not catalogued: https://orbitaldebris.jsc.nasa.gov/quarterly-news/pdfs/odqnv23i1.pdf

Nevertheless, they are tracked not because they are "visible" (in visible wavelengths), but overwhelmingly observed through radar. About a third of them are attributable to ASAT tests or the Iridium-Kosmos collision (i.e. small fragments).

Are you seriously apples-to-apples comparing the visibility of a O(10 cm)-sized piece of debris (exponentially -see 1998 debris model slideplayer.com/slide/12934272/- the vast majority of the tracked debris you mention) with tens of thousands of actual 15-meter-long functioning satellites?

Are you seriously comparing the CR stochastic noise to satellites passing in front of your FOV?

No paper-quoting is needed when you are twisting basic concepts. Please spare us such crude misinformation.

[Semmel]

I want to provide some context for the numbers in the last posts.

There are about 17000 space debries objects in the sky that are tracked. These are all tracked because they are visible. The tracking telescopes are small compared to the big astronomical telescopes, so that number is probably not the upper limit for astronomical observations. Any pixel or spectrum that any of these objects touch is garbage. And it is dealt with in data reduction pipelines. Additional 5000 or even 12000 satellited dont even make this worse by a factor of 2.

Cosmic rays are an effect that happens to long exposures high up in the atmosphere. All astronomical instruments are subject to cosmic rays. I have brought you some, see the appendix. This is a small section of a detector image from the MUSE instrument, working on one of the ESO VLTs on Paranal. The image is a dark image (closed shutter) with an exposure time of 1 hour. These things are there all the time. They are the reason why you never take only one frame of an object, always at least 2.

The point I am making: There are plenty of effects that need to be handled. Astronomy will not be over due to Starlink et al. The true impact has to be calculated by a very careful analysis that take everything else into account. If anyone finds a paper, please tell me!

Nope, the number of catalogued objects in orbit is >19000, and several thousands more are tracked but not catalogued: https://orbitaldebris.jsc.nasa.gov/quarterly-news/pdfs/odqnv23i1.pdf

Nevertheless, they are tracked not because they are "visible" (in visible wavelengths), but overwhelmingly observed through radar. About a third of them are attributable to ASAT tests or the Iridium-Kosmos collision (i.e. small fragments).

Are you seriously apples-to-apples comparing the visibility of a O(10 cm)-sized piece of debris (exponentially -see 1998 debris model slideplayer.com/slide/12934272/- the vast majority of the tracked debris you mention) with tens of thousands of actual 15-meter-long functioning satellites?

Are you seriously comparing the CR stochastic noise to satellites passing in front of your FOV?

No paper-quoting is needed when you are twisting basic concepts. Please spare us such crude misinformation.

Ok, my bad on the space debrees. I thought they are tracked optically. But I dont compare any satellites to anything. I compare the effect on the images of telescopes. A satellite looks similar enough to a cosmic ray in the sense that if you take a series of images of the same location on sky, you see them in one image and not in the others. I dont think misinformation is the right term here. Also I DO think a paper is necessary to collect all relevant information and proper context as well as analyse impact. Its not as easy and opinionated one might think.

[envy887]

I want to provide some context for the numbers in the last posts.

There are about 17000 space debries objects in the sky that are tracked. These are all tracked because they are visible. The tracking telescopes are small compared to the big astronomical telescopes, so that number is probably not the upper limit for astronomical observations. Any pixel or spectrum that any of these objects touch is garbage. And it is dealt with in data reduction pipelines. Additional 5000 or even 12000 satellited dont even make this worse by a factor of 2.

Cosmic rays are an effect that happens to long exposures high up in the atmosphere. All astronomical instruments are subject to cosmic rays. I have brought you some, see the appendix. This is a small section of a detector image from the MUSE instrument, working on one of the ESO VLTs on Paranal. The image is a dark image (closed shutter) with an exposure time of 1 hour. These things are there all the time. They are the reason why you never take only one frame of an object, always at least 2.

The point I am making: There are plenty of effects that need to be handled. Astronomy will not be over due to Starlink et al. The true impact has to be calculated by a very careful analysis that take everything else into account. If anyone finds a paper, please tell me!

How does closing the shutter affect the signal to noise ratio? For example, a 10 minute exposure 11 minutes containing 1 minute of closed shutter time?

Concerning back-of-the-envelope estimates - here's an actual accurate simulation of visible satellites if the full 12k constellation was up in their operational orbits. The absurd sky dominance is considering worst-case illumination conditions in the summer - of course that's also when best weather is available for observations. And this is for *just* the baseline Starlink, in visible wavelengths and not accounting for under-maintenance sats (lower orbits). It is left as an exercise to the reader to add a few competing such constellations, such as the 5 already in the works (totaling approximately as many birds as a 12k Starlink).





More complete blog post with naked-eye visibility and detailed effects on an observation target here (although again under simplifying assumptions of no reflections, no under-maintenance birds): http://www.deepskywatch.com/Articles/Starlink-sky-simulation.html

Showing all the existing satellites/debris with oversized/overbrightness icons like that, instead of as point sources of realistic brightness, would produce a rather similar terrifying simulation which has equally little basis in reality.

Starlinks do appear to be quite a bit brighter than most other LEO objects, which is a problem SpaceX needs to work on, and has committed to fixing. But they aren't that bright, as the realistic brightness simulation on that page shows.

While the simulation is interesting, this point has to be made with numbers, e.g. number of passes per square degree per minute at a given magnitude. I think we have enough data to simulate that for the major observatory locations. Does any know of such a simulation?

[eeergo]

But I dont compare any satellites to anything. I compare the effect on the images of telescopes.

You are saying 17000 (or 19000 or whatever) pieces of debris will have a similar effect on observational astronomy, or smaller, than the 12k Starlink constellation. That, without going into any thoughtful analysis, just because of size distribution as I explained and provided reference for, is BS.

A satellite looks similar enough to a cosmic ray in the sense that if you take a series of images of the same location on sky, you see them in one image and not in the others. I dont think misinformation is the right term here.

It is either blatant disinformation or wild disregard for your lack of knowledge about this topic (starting by the fact you didn't know most debris is tracked by radar, not by optical telescopes, which you can find in Wiki or NASA's public outreach space debris site, the two top results if you search for "space debris") - you choose.

Just for completeness, although I imagine most members here would know this: cosmic rays produce instantaneous, stochastic events whose effect is well understood and "easily" accounted for, just like thermal noise in the detector plane and other such spurious jitter. Dozens of visible satellites drifting over an exposure over tens of seconds are not.

Also I DO think a paper is necessary to collect all relevant information and proper context as well as analyse impact. Its not as easy and opinionated one might think.

You DO think so while neglecting to look at basic information with which to back your claims. You're not gonna find a paper about the effect of mosquitoes flying in front of the telescope or something, just because that isn't an issue. Similarly, papers aren't needed to disprove baseless claims.

I have been providing simulations by professional astronomers, and there are plenty of concerned such people out there speaking out, with increasingly accurate qualitative and quantitative analysis, whose message is pretty coherent. That is proper context, not orbital debris numerology.

[Semmel]

How does closing the shutter affect the signal to noise ratio? For example, a 10 minute exposure 11 minutes containing 1 minute of closed shutter time?

First, we are talking optical detectors here, not infrared because IR detectors stack long exposures from 1 to 10 second sub-exposures. The noise content of ground based astronomy in the optical (say 350 to 1000nm wavelength) is dominated by sky background and read out noise. Both are not effected by an additional 1 minute of closed shutter time. The dark current in these detectors is about 1 electron per hour. Readout noise is 2.5e per readout and sky background is larger still. Think of these numbers as standard deviation of a normal distribution. They reduce the signal to noise ratio.

However, the shutter it self might have an impact on the observation. You have to consider life time limits of shutters if operated much more frequently than designed. Also, not all instruments have shutters or they are too slow to open and close within a ~1 second which would be required for such an application.

[envy887]

Are you seriously apples-to-apples comparing the visibility of a O(10 cm)-sized piece of debris (exponentially -see 1998 debris model slideplayer.com/slide/12934272/- the vast majority of the tracked debris you mention) with tens of thousands of actual 15-meter-long functioning satellites?

Above 5,000 km, optical telescopes become the primary sensors; these have the sensitivity to track meter-sized objects in GEO

https://www.nap.edu/read/4765/chapter/5#34

Since GEO is ~100x further away, and meter-sized objects are ~100x larger in area than 10 cm objects, this suggests that 10-cm class debris in lower LEOs will produce a streak, especially with very large telescopes, sufficient to negate the usefulness of the directly effected pixels on that exposure.

Of course that streak will be very much dimmer, which is probably better for the surrounding pixels and especially better for reducing scattering in the optics that affects the whole frame.

Edit: 10-cm debris is NOT "exponentially the vast majority" of the catalog. According to CelesTrak, 7636 of the 20036 on-orbit tracked objects (38%) are either payloads or rocket bodies. While some of the payloads are cubesats in that range, most of those, and all the rocket bodies, are quite a bit larger. Based only on this, I'd say it's likely that roughly half of LEO objects are at least 1 meter in one dimension. There should be radar cross-section data available with more detail, though I can't find any recent data at the moment.

[Semmel]

But I dont compare any satellites to anything. I compare the effect on the images of telescopes.

You are saying 17000 (or 19000 or whatever) pieces of debris will have a similar effect on observational astronomy, or smaller, than the 12k Starlink constellation. That, without going into any thoughtful analysis, just because of size distribution as I explained and provided reference for, is BS.

And I acknowledged that I made a mistake with the tracking of space debries. So you can disregard that part.

A satellite looks similar enough to a cosmic ray in the sense that if you take a series of images of the same location on sky, you see them in one image and not in the others. I dont think misinformation is the right term here.

It is either blatant disinformation or wild disregard for your lack of knowledge about this topic (starting by the fact you didn't know most debris is tracked by radar, not by optical telescopes, which you can find in Wiki or NASA's public outreach space debris site, the two top results if you search for "space debris") - you choose.

Not sure why you make this personal. Please stop.

Just for completeness, although I imagine most members here would know this: cosmic rays produce instantaneous, stochastic events whose effect is well understood and "easily" accounted for, just like thermal noise in the detector plane and other such spurious jitter. Dozens of visible satellites drifting over an exposure over tens of seconds are not.

It doesnt matter if a signal is instantaneous on the detector or applied over a longer period of time. What counts is the signal at the time of readout. If you take a series of exposures, a satellite would only be present in one of this stack of images. Just like cosmic rays.

Also I DO think a paper is necessary to collect all relevant information and proper context as well as analyse impact. Its not as easy and opinionated one might think.

You DO think so while neglecting to look at basic information with which to back your claims. You're not gonna find a paper about the effect of mosquitoes flying in front of the telescope or something, just because that isn't an issue. Similarly, papers aren't needed to disprove baseless claims.

I have been providing simulations by professional astronomers, and there are plenty of concerned such people out there speaking out, with increasingly accurate qualitative and quantitative analysis, whose message is pretty coherent. That is proper context, not orbital debris numerology.

I want to find a paper that tells me all the relevant effects. A paper that outlines all the effects that are considered and the impact on astronomical observations. Many people, me included, are not qualified to do this properly. I would bet with all the attantion, at least LSST would publish something soon.

[eeergo]

Concerning back-of-the-envelope estimates - here's an actual accurate simulation of visible satellites if the full 12k constellation was up in their operational orbits. The absurd sky dominance is considering worst-case illumination conditions in the summer - of course that's also when best weather is available for observations. And this is for *just* the baseline Starlink, in visible wavelengths and not accounting for under-maintenance sats (lower orbits). It is left as an exercise to the reader to add a few competing such constellations, such as the 5 already in the works (totaling approximately as many birds as a 12k Starlink).
[...]

Showing all the existing satellites/debris with oversized/overbrightness icons like that, instead of as point sources of realistic brightness, would produce a rather similar terrifying simulation which has equally little basis in reality.

Actually, it is quite grounded in reality. Of course you're not gonna see such objects with your naked eye, but observatories mostly WILL, as long as they're somewhat illuminated - that's the issue. And this is neglecting other proposed constellations or Starlink expansions (up to 4x as many sats proposed, remember), satellites under maintenance in lower or graveyard orbits, "flashers", and impacts beyond VIS.

Starlinks do appear to be quite a bit brighter than most other LEO objects, which is a problem SpaceX needs to work on, and has committed to fixing. But they aren't that bright, as the realistic brightness simulation on that page shows.

I'm not sure the problem is actually a superior reflectivity compared to other typical LEO sats of their size (but it might be too) - the majority of this reaction comes from the *number* of them, and what they might lead to with expansions/competition.

While the simulation is interesting, this point has to be made with numbers, e.g. number of passes per square degree per minute at a given magnitude. I think we have enough data to simulate that for the major observatory locations. Does any know of such a simulation?

As mentioned, if a satellite is illuminated it will generally be an impact to astronomy / astrophotography, so the simulation showing every sat at the same magnitude should be a good approximation, especially since it makes some conservative assumptions on the other hand. Looks like the realistic brightness simulation could be easily modified to show only satellites over a certain magnitude. I haven't seen any figure for passes/sq2/min/mag yet.