Impacts of Large Satellite Constellations on Astronomy

[eeergo]

Wrong, groundbased telescope can be used to track LEO debris less than 10cm.

Fact: I said most of the tracked objects are not, or barely, visible optically, for current tracking optical telescopes.
Fact: Most of the tracked objects in LEO are debris.
Fact: I did *not* say they were in principle "invisible", i.e. could not be seen optically.
Fact: Comparing apples-to-apples the visibility of a random piece of small debris to a 15-m reflective satellite is a fallacy
Fact: The overwhelming majority of LEO object population is tracked through radar, especially sub-decimeter objects.

Fact: What you quote as wrong is actually right.

Irrelevant fact: A sensitive enough telescope can view illuminated objects a few hundred kilometers away against a black background.

What result? He showed some animation of Starlink going around the sky, this proves nothing.

He did make quite some more visibility studies than "an animation", which were not previously available anywhere, and which complement less-straightforward others done by professionals (see Cees Bassa's). Maybe if you ask him nicely he can provide you with a variant of just the projected telescope-visible units - it should be trivial to make with the machinery he put in place.

By the way, with the potential high stakes of this project, it is the active party who has to prove negligible impact, not the ones who suffer from it. You're claiming in several posts that claims for Starlink (and I guess other megaconstellations) having large impacts is baseless - where's your proof?

Useless analog, you're intentionally ignoring the only other professional astronomer that did the calculation and showed a result of minimal impact.

It's clear no serious studies have been made, from the LSST's own confusing statements - that's at the moment clearly on the astronomical community's shoulders. Why are you believing his numbers though when just a quote is provided, with no details, and not the ones from plenty of others? The more simulations are made, even with benign assumptions and simplifications, the clearer the trend is that, without serious mitigation and coordination, the constellation would be quite damaging.

I guess Cees Bassa, James Lowenthal, Anthony Tyson or Daniel Marín are also baseless amateurs, as are the many professional astronomers (disorganizedly) speaking out every day.

Show me the numbers. Without numbers, it doesn't matter what they speak, this is science, not astrology.

This is insulting to the quoted people, and to me as a related professional. And a bit to you too, who choose to ignore the many arguments and numbers presented.

1. SpaceX is cooperating with AAS to satisfy the need of LSST, this basically mitigate all the concerns in the statements you listed.
2. AAS is clearly following a live and let live path where both constellation and astronomy can co-exist, as AAS is the organization representing all US astronomers, I take this to be the sentiment of astronomers at large.

AAS (and other scientific organizations in general) do not have the influence, public perception or PR machinery SpaceX, or other telecoms, have. Their position of inferiority, and being busy with -you know- science rather than tracking down some telecom's latest proprietary constellation plans, demands a cooperative approach.

Cooperation is anyway needed, and no-one is suggesting to close space to business so that astronomy can flourish. Mindlessly spamming it with poorly-planned regulations, or trying to patch it when tens of thousands sats (and billions of $) are flying overhead fait-accompli, and when ground-based cheaper alternatives exist for the business model, is another thing.

[eeergo]

I admire your persistence. I largely gave up on this thread a while ago.

I can be stubborn Planning to quickly overtake nature by more-or-less frivolous profit-oriented reasons never fails to irk me, especially when defense for that attitude is more ideological than well-thought. Plus I'm buttoning up a project to move on to a nicer one after Christmas, so that frees up some will to get down to the mud

Tangentially on CRs, depends what you mean by "filtered out". [...]

Thanks for the complementary perspective. As for the coatings, as others have pointed out, I wonder how effective a flat black panel will be at reducing visibility anyway, or how acceptable (to SpaceX) the impacts to operability/business brought about by more radical/effective solutions would be. It's a good initiative though, I just fear based on what we've seen that effective mitigation will only come after a large irreversible impact has been done.

[jebbo]

This is an impact I hadn't even considered: @ATel alerts for transient events (fast radio bursts, gamma ray bursts and in this case a neutron star-neutron star merger candidate) are often poorly localised on the sky and a rapid wide-field survey is required to try and find an optical (or other wavelength) counterpart.

For gravitational waves in particular, the source galaxies are distant, and hence long exposure times are needed.

The existing few satellites are already having an impact on these observations (compare the brightnesses in the 2nd image).

https://twitter.com/GOTOObservatory/status/1206708402937712640

--- Tony

[eeergo]

This is an impact I hadn't even considered: @ATel alerts for transient events (fast radio bursts, gamma ray bursts and in this case a neutron star-neutron star merger candidate) are often poorly localised on the sky and a rapid wide-field survey is required to try and find an optical (or other wavelength) counterpart.

For gravitational waves in particular, the source galaxies are distant, and hence long exposure times are needed.

The existing few satellites are already having an impact on these observations (compare the brightnesses in the 2nd image).

--- Tony

Exactly, that's also the other critical side of this controversy for such global, radical infrastructures: the rush to get it up there, the lack of effort to look for alternatives or mitigation, the feet-dragging from regulators, the short-sightedness of the scientific community... all contribute to not having a good handle of what the impacts will actually be, from details on the obvious to the very existence of more subtle ones.

[su27k]

Wrong, groundbased telescope can be used to track LEO debris less than 10cm.

Fact: I said most of the tracked objects are not, or barely, visible optically, for current tracking optical telescopes.

Which is clearly wrong, as NASA's LMT was able to detect debris less than 10cm, as small as 1cm.

Fact: Most of the tracked objects in LEO are debris.
Fact: I did *not* say they were in principle "invisible", i.e. could not be seen optically.

You said "they are tracked not because they are "visible" (in visible wavelengths)", while in fact NASA did and is still doing some visual tracking of space debris.

Fact: Comparing apples-to-apples the visibility of a random piece of small debris to a 15-m reflective satellite is a fallacy

No, it's not. Debris would generate similar trails as satellite, just smaller, it's a matter of degree, but the effect and mitigation could be similar, which is the point the OP trying to make.

It is also a fallacy to say Starlink is 15-m long, that's the solar panel size, you have no evidence to show solar panel is the issue here. In fact it's probably not, since SpaceX is not attempting to coat the solar panel.

Fact: The overwhelming majority of LEO object population is tracked through radar, especially sub-decimeter objects.

This was already covered by the book I quoted, NASA's visual tracking telescope funding was cut, that's why they're relying on radar.

Fact: What you quote as wrong is actually right.

Already proven to be false.

What result? He showed some animation of Starlink going around the sky, this proves nothing.

He did make quite some more visibility studies than "an animation", which were not previously available anywhere, and which complement less-straightforward others done by professionals (see Cees Bassa's). Maybe if you ask him nicely he can provide you with a variant of just the projected telescope-visible units - it should be trivial to make with the machinery he put in place.

It doesn't matter, it's still an animation, not a study of the impact on astronomy, which is the topic of this thread.

By the way, with the potential high stakes of this project, it is the active party who has to prove negligible impact, not the ones who suffer from it. You're claiming in several posts that claims for Starlink (and I guess other megaconstellations) having large impacts is baseless - where's your proof?

I already presented that the calculation done by Olivier Hainaut showed impact to ESO is minimal, there's also the early result from LSST team.

And no, SpaceX doesn't have to prove negligible impact, because there is no regulation that says satellites must have negligible impact to astronomy.

Useless analog, you're intentionally ignoring the only other professional astronomer that did the calculation and showed a result of minimal impact.

It's clear no serious studies have been made, from the LSST's own confusing statements - that's at the moment clearly on the astronomical community's shoulders. Why are you believing his numbers though when just a quote is provided, with no details, and not the ones from plenty of others?

I can ask the same question, why are you believing LSST team's latest number, "when just a quote is provided, with no details, and not the ones from plenty of others", plus they're contradicting their own early result?

The more simulations are made, even with benign assumptions and simplifications, the clearer the trend is that, without serious mitigation and coordination, the constellation would be quite damaging.

There is no such trend, there's only 3 data points, 2 with minimal impact, one with non-minimal impact. And two of the data points are concerning one telescope, out of many in the world. Your attempt at generalization using so small dataset is un-scientific.

I guess Cees Bassa, James Lowenthal, Anthony Tyson or Daniel Marín are also baseless amateurs, as are the many professional astronomers (disorganizedly) speaking out every day.

Show me the numbers. Without numbers, it doesn't matter what they speak, this is science, not astrology.

This is insulting to the quoted people, and to me as a related professional. And a bit to you too, who choose to ignore the many arguments and numbers presented.

So asking scientists to present numbers and calculations is insulting? I don't think the general scientific community would agree, in fact I believe it is grossly unethical for scientists to pass their personal opinion as scientific truth without showing the supporting data and calculations.

1. SpaceX is cooperating with AAS to satisfy the need of LSST, this basically mitigate all the concerns in the statements you listed.
2. AAS is clearly following a live and let live path where both constellation and astronomy can co-exist, as AAS is the organization representing all US astronomers, I take this to be the sentiment of astronomers at large.

AAS (and other scientific organizations in general) do not have the influence, public perception or PR machinery SpaceX, or other telecoms, have. Their position of inferiority, and being busy with -you know- science rather than tracking down some telecom's latest proprietary constellation plans, demands a cooperative approach.

That's pure speculation, you don't know what AAS' rational is, stop pretending you do. It is entirely possible they're more reasonable than you and realizes the sky is not an exclusive resource belongs only to astronomy.

Cooperation is anyway needed, and no-one is suggesting to close space to business so that astronomy can flourish. Mindlessly spamming it with poorly-planned regulations, or trying to patch it when tens of thousands sats (and billions of $) are flying overhead fait-accompli, and when ground-based cheaper alternatives exist for the business model, is another thing.

Business will take care of itself, neither you nor the scientific community has any way to judge if the business is viable, nobody does, only the market can do it. But hey, if like you said the satellites are too expensive and couldn't compete with ground based cheaper alternatives, then the constellation business will fail, and satellites will deorbited, and impact to astronomy will disappear, so what's the problem?

This is why your ranting about "tens of thousands sats (and billions of $) are flying overhead fait-accompli" makes zero sense, nobody is launching tens of thousands of satellites in one go, SpaceX's initial constellation is only one thousand, they'll only expand the constellation if it is a successful business, in which case the market would have already proved they're a better alternative than ground based solutions, and their existence have a unique value.

[Semmel]

Anyway: your knowledge of the topic *is* important when you make such definitive statements, and have continued in your latest posts even after I showed you why. In fact, from the tone of your posts here I was dubious whether you were a fellow astrophysicist or related scientist, until further ones pretty much cleared up the issue.

You're talking about data pipelines, laser guides, control software infrastructures, cosmic rays, exposures, signal at readout etc. and you don't know how an optical (or whatever) signal is integrated to optimize S/N while minimizing spurious (i.e. short-timescale) artifacts or noise? I would think that's a much more basic point you need to understand before going on to discuss fixes:

I still dont get why my level of knowledge is in any way relevant. If my rambling doesnt make sense, then say why it doesnt make sense and tell me how it is correct and I learn something. This back and forth on my knowledge is off topic and I will ignore it from now on.

CRs can be efficiently filtered out because their discharge time on the detector is very short, while astronomical targets are fixed and/or tracked. It's not that the images without them (none) are selected out. Same concept for dim quick objects (on the timescale of the long exposures needed to image large-magnitude targets) that don't saturate the detector, BUT obviously they won't ever be as quick or random as CRs, so their impact will be greater, although in many cases they *can* be just picked out of the image stack.

You still didnt explain why my statement is wrong. I repeat in different words, maybe it becomes clearer then. If you have a CCD (there are practically no CMOS optical detectors in astronomy) and take an exposure of several seconds to minutes.
- Cosmic rays will create image artifacts as provided in the image above. This happens practically instantaneously.
- When a satellite crosses the field of view of a telescope, it creates a streak within maybe a second or so.

Its not important how that happens physically, both effects show up as detected flux in the image after reading it out. The important commonality is, that in a series of observations, the streak of one satellite will only be visible in one frame of many. Hence, the satellite is relatively easy to identify as an artifact that doesnt belong to an astronomical target, just like a cosmic ray. A cosmic ray only ever strikes once at one location of the CCD and there are practically never 2 identical or even similar cosmic rays at the exact same location of the CCD in consecutive frames. Obviously they will both reduce the signal to noise in the pixels they strike, or render them useless outright. That depends very much on your data reduction skills, science, type of instrument, etc.

I have no idea why you question that logic. So please explain whats wrong with it. I have no idea what the discharge time of cosmic rays have to do with any of the above.

[eeergo]

I still dont get why my level of knowledge is in any way relevant. If my rambling doesnt make sense, then say why it doesnt make sense and tell me how it is correct and I learn something. This back and forth on my knowledge is off topic and I will ignore it from now on.

Good. While you're at it don't post categorical statements when you don't know the basic principles acting on it for a fact (i.e. tracked debris exist <=> they are optically visible, among others that followed).

You still didnt explain why my statement is wrong. I repeat in different words, maybe it becomes clearer then. If you have a CCD (there are practically no CMOS optical detectors in astronomy) and take an exposure of several seconds to minutes.
- Cosmic rays will create image artifacts as provided in the image above. This happens practically instantaneously.
- When a satellite crosses the field of view of a telescope, it creates a streak within maybe a second or so.

Wrong. That's where your logic breaks down. Wildly different timescales, brightness profile... Nothing to do with instantaneous CR discharges, unless you're just taking a long integration, which isn't done for reasons ranging from atmospheric fluorescence, to overwhelming thermal and CR noise, as you correctly state elsewhere.

Its not important how that happens physically, both effects show up as detected flux in the image after reading it out. [...]

I'll make some diagrams to get this point through. More to the right means more relative impact:

Timescale on single exposure:

Instantaneous ------------------------------------------------------------------------------------------ Ground-Fixed
              CR      Thermal        Meteors            LEO sats/deb/Megaconst'             Celestial dome          GEO

(VIS) Intensity:

Invisible ------------------------------------------------------------------------------------------------------- Blinding
  Dust    24mag dome     LEO debris        GEO      Thermal          LEO sats  MegaC'   LEO flashes   CR/Meteors

Frequency on FOV:

Rare ------------------------------------------------------------------------------------------------------- Always on
Meteors   LEO flash  LEO sats                           LEO deb   Megaconst'                 GEO  Thermal/CR/targets

The most damaging thing would be something persistent, blindingly-bright and always on. As you can see, in the list of common things seen by visible telescopes, there wouldn't be anything as consistently to the right as megaconstellations.

[eeergo]

Oh, walls of text in response to the same overarching topics, how I missed you. Hint: trim your quotes.
Apologies for the long post that results even when ignoring some filler and general "markets will regulate themselves" political views that have worked so well so many times in global-scale issues such as this.

Which is clearly wrong (most of the tracked objects are not, or barely, visible optically, for current tracking optical telescopes)[/size], as NASA's LMT was able to detect debris less than 10cm, as small as 1cm.

Key words: current, overwhelmingly.
Decimeter-scale objects were also tracked on the Moon. It's still not relevant.

No, it's not [Comparing apples-to-apples the visibility of a random piece of small debris to a 15-m reflective satellite is a fallacy][/size]. Debris would generate similar trails as satellite, just smaller, it's a matter of degree, but the effect and mitigation could be similar, which is the point the OP trying to make.  It is also a fallacy to say Starlink is 15-m long, that's the solar panel size, you have no evidence to show solar panel is the issue here. In fact it's probably not, since SpaceX is not attempting to coat the solar panel.

A speck of paint, or a fungal spore, would generate a similar trail as a satellite, just smaller - it's a matter of degree. The effect and mitigation would be similar. Find the fallacy. A 15m^2 glass surface pointing zenith, which needs to see the Sun as much as possible, is not the issue. Its impact is comparable to decimeter-scale debris. Find the fallacies again.

He did make quite some more visibility studies than "an animation", [...]

It doesn't matter, it's still an animation, not a study of the impact on astronomy, which is the topic of this thread.

I should just ignore this retort and save some space, but it's too audacious to let pass. Readers, please do bask in its willful brushing-aside.

And no, SpaceX doesn't have to prove negligible impact, because there is no regulation that says satellites must have negligible impact to astronomy.

There was also no regulation to protect forests, blue whales or throw waste in the ocean. Shouldn't they have been implemented when the problems started arising, instead of when they were unmanageable? That's the issue here.

I already presented that the calculation done by Olivier Hainaut showed impact to ESO is minimal, there's also the early result from LSST team. I can ask the same question, why are you believing LSST team's latest number, "when just a quote is provided, with no details, and not the ones from plenty of others", plus they're contradicting their own early result?

It's called refining results, having more data and time available to weigh in more factors, allowing other people to study it and reach broader-consensus conclusions. In short: scientific process. Why am I spelling this out? By the way, after "astrology" you've added "unscientific", your headcount of insulting expressions is reaching dangerous levels.

So asking scientists to present numbers and calculations is insulting? I don't think the general scientific community would agree, in fact I believe it is grossly unethical for scientists to pass their personal opinion as scientific truth without showing the supporting data and calculations.

Asking questions about Starlink is anti-SpaceX, anti-progress, and generally poor taste.

Yet it's wonderful to qualify as "baseless" the concerns voiced by major international astronomical institutions, plenty of professionals online (not just the 3 I listed, mind you) and respected enthusiasts is unscientific, unless audit-level analyses are disseminated "presto", even in spite of the public unavailability of crucial proprietary basic characteristics of the constellations - because some two early estimates might have been conservative, one of which being a single-sentence quote on an interview. But of course.

That's pure speculation, you don't know what AAS' rational is, stop pretending you do. It is entirely possible they're more reasonable than you and realizes the sky is not an exclusive resource belongs only to astronomy.

Headcount of insults: +1. By the way, you don't get to tell me when to stop, especially since I do belong to the community you're referring to.

I'm no AAS spokesperson, so I can't know for certain the rationale for being conciliatory (neither do you, so don't attribute the reasonable perspective to yourself). My statement about their inferiority position is undeniably true in any case, as is their lack of crucial parameters with which to reliably advance their studies. General good will/manners, plus applying the principle of caution you appear to disregard, would probably count towards their attitude.

[Semmel]

You still didnt explain why my statement is wrong. I repeat in different words, maybe it becomes clearer then. If you have a CCD (there are practically no CMOS optical detectors in astronomy) and take an exposure of several seconds to minutes.
- Cosmic rays will create image artifacts as provided in the image above. This happens practically instantaneously.
- When a satellite crosses the field of view of a telescope, it creates a streak within maybe a second or so.

Wrong. That's where your logic breaks down. Wildly different timescales, brightness profile... Nothing to do with instantaneous CR discharges, unless you're just taking a long integration, which isn't done for reasons ranging from atmospheric fluorescence, to overwhelming thermal and CR noise, as you correctly state elsewhere.

So how long do you think it takes a satellite in LEO to cross the field of view of a telescope? What exposure times are you talking about?

Its not important how that happens physically, both effects show up as detected flux in the image after reading it out. [...]

I'll make some diagrams to get this point through. More to the right means more relative impact:

Timescale on single exposure:

Instantaneous ------------------------------------------------------------------------------------------ Ground-Fixed
              CR      Thermal        Meteors            LEO sats/deb/Megaconst'             Celestial dome          GEO

(VIS) Intensity:

Invisible ------------------------------------------------------------------------------------------------------- Blinding
  Dust    24mag dome     LEO debris        GEO      Thermal          LEO sats  MegaC'   LEO flashes   CR/Meteors

Frequency on FOV:

Rare ------------------------------------------------------------------------------------------------------- Always on
Meteors   LEO flash  LEO sats                           LEO deb   Megaconst'                 GEO  Thermal/CR/targets

The most damaging thing would be something persistent, blindingly-bright and always on. As you can see, in the list of common things seen by visible telescopes, there wouldn't be anything as consistently to the right as megaconstellations.

If you have quantitative plots for these? I agree with the ordering, but numbers matter a lot here. What you you say seems to be correct but nothing seems to prove my statement wrong. I have the feeling you dont understand what I am saying. Maybe you can explain with your own words of what you think I say, so we can stop talking past each other.

[envy887]

Frequency on FOV:

Rare ------------------------------------------------------------------------------------------------------- Always on
Meteors   LEO flash  LEO sats                           LEO deb   Megaconst'                 GEO  Thermal/CR/targets

The most damaging thing would be something persistent, blindingly-bright and always on. As you can see, in the list of common things seen by visible telescopes, there wouldn't be anything as consistently to the right as megaconstellations.

If you have quantitative plots for these? I agree with the ordering, but numbers matter a lot here. What you you say seems to be correct but nothing seems to prove my statement wrong. I have the feeling you dont understand what I am saying. Maybe you can explain with your own words of what you think I say, so we can stop talking past each other.

The frequency ordering depends strongly on which megaconstellation deployment scenarios we are considering. The ~2200 bird combined initial deployments of Starlink and Oneweb will still be greatly outnumbered by the ~7600 existing satellites/rocket bodies and vastly outnumbered by the ~15,000 debris. Even the full authorized ~15,000 satellite deployment of Starlink and Oneweb would be  outnumbered by visible debris.

The above ordering is only correct for the requested but unauthorized deployment of 30,000+ satellites.

[envy887]

... It's a good initiative though, I just fear based on what we've seen that effective mitigation will only come after a large irreversible impact has been done.

The very bright VLEO satellites are hardly irreversible. They will decay within weeks of their propellant running out or any system failure.

The ones at 800+ km are far more concerning in terms of orbital lifetime, but they are also much, much dimmer simply due to distance.

[eeergo]

So how long do you think it takes a satellite in LEO to cross the field of view of a telescope? What exposure times are you talking about?

It's obviously a function of the FOV of course, but unless it's comparable to the integration time for a single exposure of such a narrow FOV, it will be a distinct issue.

Let's check it back-of-the-envelope: apparent angular speed for LEO is ~0.75º/s. You should be doing short integrations to avoid thermal noise and CRs (yet long enough for sensitivity), apparently O(100)ms is typical. The CR track will be instantaneous, so it will last that long.

Therefore, the FOV for a transiting satellite to have similar impact (with respect to persistence on the frame) as the CR would be:
0.75 º/s * 0.1 s = 0.075º -> 0.075º x 0.075º=0.005625 sqº
or ~20 arcsec^2 or 0.33 arcmin^2. This is on the order of single *pixels*, according to Keck's searchable specs or ESO's VISTA telescope (who has a FOV of 1.65º diameter, i.e. approximately 300x more).

So yes, we're talking about a 2-3 order of magnitude different effect, at least.

I'll make some diagrams to get this point through. [...]

If you have quantitative plots for these? I agree with the ordering, but numbers matter a lot here. What you you say seems to be correct but nothing seems to prove my statement wrong. I have the feeling you dont understand what I am saying. Maybe you can explain with your own words of what you think I say, so we can stop talking past each other.

I have made my best attempt at explaining a very basic issue, that directly contradicts what you're saying (that it CRs and satellite passes are comparable, and more LEO sats shouldn't really worsen things much). I don't see why I'm talking past you and your statement stands unchallenged. If I had numbers for this I would be writing a review paper - but I'm pretty confident about the ordering, scale and impact conclusion.

[eeergo]

The frequency ordering depends strongly on which megaconstellation deployment scenarios we are considering. The ~2200 bird combined initial deployments of Starlink and Oneweb will still be greatly outnumbered by the ~7600 existing satellites/rocket bodies and vastly outnumbered by the ~15,000 debris. Even the full authorized ~15,000 satellite deployment of Starlink and Oneweb would be  outnumbered by visible debris.

The above ordering is only correct for the requested but unauthorized deployment of 30,000+ satellites.

Yes indeed. Still, megaconstellations would score high, and would continue to be too high on both other two variables (timescale and intensity). Furthermore, they wouldn't provide their expected market disruption with just O(1000) birds. The problem is much more marginal for initial deployments in the thousands, that's obvious. But those are also inevitable barring a catastrophe, given the 2020/21 launch plans from SpaceX. We're talking about things that can be changed, and final-state constellations.

Plus you'd rely on little to no competition, or copycats from other countries (I'm looking at China), to double/triple/quadruple/quintuple that - while still ignoring the greater-impact lower-orbiting malfunctioned/under-maintenance/replenishments sets.

The very bright VLEO satellites are hardly irreversible. They will decay within weeks of their propellant running out or any system failure.

The ones at 800+ km are far more concerning in terms of orbital lifetime, but they are also much, much dimmer simply due to distance.

The effective lifetime of a VLEO subconstellation of hundred-strong decaying units tends to infinity when you consider the rate of failure/replenishment/maintenance a bunch of megaconstellations with tens of thousands of birds will need.

[jebbo]

On FOV, exposure time, etc, it's worth considering the images in the tweet from the GOTO Observatory I posted earlier.

This image covers 10 degrees by 5.5 degrees, using a 40cm aperture f2.5 lens (so a very cheap telescope). The galaxy shown in the close-up is ARP 271 which is 11.8 mag and relatively close (60Mpc ish from memory) - hence the pixels there are saturated.

The image is looking for objects that are 10x or more further away than ARP 271, so much fainter. Hence the exposure time of 10s of seconds.

What is problematic here is the Starlink streaks are saturated and at least 10 pixels wide, so they will be obscuring a large number of the faint galaxies the image is looking at for changes.

Edit: this instrument is typical of those used for rapid followup of transients. The whole point is to look quickly at large chunks of the sky.

--- Tony

[envy887]

The frequency ordering depends strongly on which megaconstellation deployment scenarios we are considering. The ~2200 bird combined initial deployments of Starlink and Oneweb will still be greatly outnumbered by the ~7600 existing satellites/rocket bodies and vastly outnumbered by the ~15,000 debris. Even the full authorized ~15,000 satellite deployment of Starlink and Oneweb would be  outnumbered by visible debris.

The above ordering is only correct for the requested but unauthorized deployment of 30,000+ satellites.

Yes indeed. Still, megaconstellations would score high, and would continue to be too high on both other two variables (timescale and intensity). Furthermore, they wouldn't provide their expected market disruption with just O(1000) birds. The problem is much more marginal for initial deployments in the thousands, that's obvious. But those are also inevitable barring a catastrophe, given the 2020/21 launch plans from SpaceX. We're talking about things that can be changed, and final-state constellations.

Plus you'd rely on little to no competition, or copycats from other countries (I'm looking at China), to double/triple/quadruple/quintuple that - while still ignoring the greater-impact lower-orbiting malfunctioned/under-maintenance/replenishments sets.

The very bright VLEO satellites are hardly irreversible. They will decay within weeks of their propellant running out or any system failure.

The ones at 800+ km are far more concerning in terms of orbital lifetime, but they are also much, much dimmer simply due to distance.

The effective lifetime of a VLEO subconstellation of hundred-strong decaying units tends to infinity when you consider the rate of failure/replenishment/maintenance a bunch of megaconstellations with tens of thousands of birds will need.

The 1600 sat initial Starlink deployment could reasonably generate up to $10+B/yr revenue for SpaceX, which is about 5x their launch revenue. It's potentially enough for significant market disruption and also for SpaceX to proceed with their Mars goals. I would not assume that 10k+ satellite constellations will necessarily be launched, at least for a decade or more.

My point about the lifetime of VLEO sats is that mitigation can be iterative and the earlier, brighter satellites will not be up long. They can be replaced by newer, dimmer designs in the roll-out and maintenance process. It's entirely possible that most of the currently flying Starlinks will be gone before LSST even enters operation in 2+ years. So while the constellation might tend towards an infinite lifetime, the impact should not.

The point about the Chinese etc followons is well made, though. That is going to require international agreements to keep things manageable. Doesn't radio astronomy currently benefit from such agreements?

[gongora]

Ok, new short term rule for this thread.  If I see a post with more than 3 quotes in it then it will be deleted.  I don't care whose post it is, or if the information is good or not.  This carving up a post into 20 pieces so you can refute it line by line crap is pretty annoying to everyone else that has to look at it.

[gongora]

Their exact statement:

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.

Ok, that sounds totally different already. 40% of the frames during twilight have a streak.

The thing you quoted quite clearly does not say that 40% of the frames during twilight have a streak.  Maybe you should read it again.

[gongora]

There is a lot of cherry picking of quotes with little attention paid to context.  A brief lookup of the NASA LMT seems to show that it was never a major contributor to debris tracking.  While it may be possible for most debris to be tracked optically, in practice radar is used for a lot of it.  The newest systems coming online now to improve debris tracking by US entities, both government and commercial, are radar.  One of the first pieces I found on LMT also noted its detection falling off around 11cm.

[Semmel]

So how long do you think it takes a satellite in LEO to cross the field of view of a telescope? What exposure times are you talking about?

It's obviously a function of the FOV of course, but unless it's comparable to the integration time for a single exposure of such a narrow FOV, it will be a distinct issue.

Let's check it back-of-the-envelope: apparent angular speed for LEO is ~0.75º/s. You should be doing short integrations to avoid thermal noise and CRs (yet long enough for sensitivity), apparently O(100)ms is typical. The CR track will be instantaneous, so it will last that long.

So you are talking about IR astronomy, not optical. I am fully aware that IR has short frames that are stacked by the hundreds. Also dithered to limit the influence of hot pixels. But I was not talking about IR, I was talking about optical with exposure times of one frame in the 10s of seconds or minutes. No wonder we were talking past each other.

[Semmel]

Their exact statement:

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.

Ok, that sounds totally different already. 40% of the frames during twilight have a streak.

The thing you quoted quite clearly does not say that 40% of the frames during twilight have a streak.  Maybe you should read it again.

Granted. I was misreading the 40%. Yet, I cant make out what they mean exactly by that figure. The stuff I wrote and you didnt quote is not effected by that. What exactly DO they mean? Is there a more elaborate analysis somewhere?