Impacts of Large Satellite Constellations on Astronomy

[Davidthefat]

How much impact would the new constellations really have considering the current state of traffic in space?

http://stuffin.space/

[gongora]

How much impact would the new constellations really have considering the current state of traffic in space?

http://stuffin.space/

https://sattrackcam.blogspot.com/2019/05/numbers-spacex-starlink-constellation.html

[Rondaz]

AAS Issues Position Statement on Satellite Constellations..

10 Jun 2019

https://aas.org/media/press-releases/aas-issues-position-statement-satellite-constellations

[su27k]

AURA Statement on the Starlink Constellation of Satellites

The Association of Universities for Research in Astronomy (AURA) is the managing organization for many ground-based telescopes for National Science Foundation (NSF), both extant and under construction. We note that the launch of the Starlink system may have impacts on the observational capabilities of these facilities.

One facility is the Large Synoptic Survey Telescope (LSST), under construction by NSF in Chile and slated to begin wide-field imaging of the sky in 2021. LSST will create an astronomical survey that depends on dark skies for its core science. LSST’s frequent imaging of the same region of sky will be a mitigating factor for Starlink interference, providing enough uncontaminated images to reject the images that contain satellite trails or other anomalies.

In the case of the full constellation of Starlink satellites, initial calculations show that LSST images would, on average, contain about one satellite trail per visit for an hour or two after sunset and before sunrise. A very conservative upper limit on the number of LSST pixels affected by Starlink satellites is about 0.01%, and quite likely smaller. Therefore, for LSST, even a constellation of about 10,000 Starlink satellites would be a nuisance rather than a real problem.

We emphasize, however, that the impact of satellite constellations on other AURA telescopes that have wider fields, longer exposures, and/or less sophisticated data processing pipelines may be much more significant. Furthermore, Starlink may be only the first in a series of new technologies that could impact LSST and other ground-based astronomy facilities.

We believe that the design and implementation of these constellations should be undertaken in consultation with the astronomical community to minimize their impact. For a discussion of broader impact of satellites on research in astronomy, please see a statement on satellite constellations by the International Astronomical Union.

Contact:
Shari Lifson
AURA Corporate Communications
[email protected]

The bold part is the only quantitative estimate of the negative impact of Starlink to astronomy I can find so far, looks like at least in this case impact is basically non-existent.

[daveklingler]

AURA Statement on the Starlink Constellation of Satellites

The Association of Universities for Research in Astronomy (AURA) is the managing organization for many ground-based telescopes for National Science Foundation (NSF), both extant and under construction. We note that the launch of the Starlink system may have impacts on the observational capabilities of these facilities.

One facility is the Large Synoptic Survey Telescope (LSST), under construction by NSF in Chile and slated to begin wide-field imaging of the sky in 2021. LSST will create an astronomical survey that depends on dark skies for its core science. LSST’s frequent imaging of the same region of sky will be a mitigating factor for Starlink interference, providing enough uncontaminated images to reject the images that contain satellite trails or other anomalies.

In the case of the full constellation of Starlink satellites, initial calculations show that LSST images would, on average, contain about one satellite trail per visit for an hour or two after sunset and before sunrise. A very conservative upper limit on the number of LSST pixels affected by Starlink satellites is about 0.01%, and quite likely smaller. Therefore, for LSST, even a constellation of about 10,000 Starlink satellites would be a nuisance rather than a real problem.

We emphasize, however, that the impact of satellite constellations on other AURA telescopes that have wider fields, longer exposures, and/or less sophisticated data processing pipelines may be much more significant. Furthermore, Starlink may be only the first in a series of new technologies that could impact LSST and other ground-based astronomy facilities.

We believe that the design and implementation of these constellations should be undertaken in consultation with the astronomical community to minimize their impact. For a discussion of broader impact of satellites on research in astronomy, please see a statement on satellite constellations by the International Astronomical Union.

Contact:
Shari Lifson
AURA Corporate Communications
[email protected]

The bold part is the only quantitative estimate of the negative impact of Starlink to astronomy I can find so far, looks like at least in this case impact is basically non-existent.

The bold part is a quantitative estimate of the negative impact of Starlink to the LSST, not to astronomy.  By virtue of very long exposure times, satellites crossing the LSST's image field in a given exposure can be filtered out.

[daveklingler]

How much impact would the new constellations really have considering the current state of traffic in space?

http://stuffin.space/

https://sattrackcam.blogspot.com/2019/05/numbers-spacex-starlink-constellation.html

From the above post:

Below 550 km, the population would increase to three times as much as currently - and this includes all very small debris pieces that can only be observed by radar in the tally. If we restrict the comparison to the larger objects, it means an at least five times increase in object number. That is truely significant.


Further on, he says something I wholeheartedly agree with:

It seems to me that the World, the international community as a whole instead of one US corporation,  should have some say into this. I am otherwise a fan of Elon Musk, who undoubtedly has given space exploration and space technology a new impetus and good shake-up: but concerning Starlink, this all seems not well thought out to me.

From the Twitter thread by Cees Bassa, an Netherlands astronomer who posted an analysis of the effects on the night sky:

https://twitter.com/cgbassa/status/1132551806125522945

At 52 degree latitude, these 550 km orbits are illuminated throughout the night from May to mid-August. During those summer nights #Starlink satellites will be visible all the time. 

But even in the spring, autumn and winter, around half a dozen #Starlink satellites will be visible at anytime upto 3 hours before sunrise and 3 hours after sunset. Depending on how bright they end up being, this will have a drastic impact on the character of the night sky.

...

It's unclear what this would mean for a 12000 satellites, as the details of their orbits are not known. A rough guess would be to multiply these numbers by a factor of 7 (12000/1600). So around 70 to 100 satellites visible during twilight at any time and any location!

[daveklingler]

I've noticed that the AAS official statement mentions the natural night sky. That's important.

For the most part these days I'm a naked eye star lover.  I'm fine with the occasional satellite or jet aircraft passing over. I'm now getting into mirror grinding, and if, in the next few years, I'm doing some long exposures and a satellite floats through, I'll most likely shrug my shoulders and try again as I've done in the past.

But since my late teens, I've unconsciously navigated by the night sky. I look up quite a bit while I'm out at night to get my bearings without even thinking about it. I smile at the constellations as they float above me in their rightful places in their rightful seasons.  During the relatively few times I've been to large cities with poor seeing, I've been surprised to find myself disoriented and uncomfortable.

All of this is to say that I prize the natural night sky.  The addition of hundreds of objects floating quickly through it would be gut-wrenching for me and a significant portion of the other members of our species. No one at SpaceX or any of the other would-be constellation providers asked me how I felt about losing the natural sky, nor do I believe they even thought about it.  If you live in Hawthorne, the night sky is simply not there.

Although I see the obvious promise of these constellations, there's certainly a big tradeoff and the decision should not be left up to a few big corporations who plan to make billions.  My regard for Elon Musk is not so high that I think SpaceX should be able to do whatever it pleases for the supposed greater good of all humanity.  I get the idea, in fact, that Elon Musk has ideas and then just implements them without a whole lot of forethought, and uh, sometimes they work and sometimes they don't.

[ChrisWilson68]

All of this is to say that I prize the natural night sky.  The addition of hundreds of objects floating quickly through it would be gut-wrenching for me and a significant portion of the other members of our species. No one at SpaceX or any of the other would-be constellation providers asked me how I felt about losing the natural sky, nor do I believe they even thought about it.

There are far more aircraft flying at any given time than there ever will be Starlink satellites.  The aircraft are far brighter and more distracting.  The aircraft can appear at any time of night, unlike the Starlink satellites, which can only be visible near dusk or dawn, most of which time the sky is somewhat light anyway.

People are blowing this way, way out of proportion.

[ChrisWilson68]

No one at SpaceX or any of the other would-be constellation providers asked me how I felt about losing the natural sky

Actually, they did.  The submitted an application for permission to put up the constellation to the United States government.  The government, in turn, then invited input from all its citizens about their plan.  You had a chance to make this point before the constellation was approved.

There was even a fair amount of talk on this very site about the application when it was open for public comment.

[su27k]

The bold part is a quantitative estimate of the negative impact of Starlink to the LSST, not to astronomy. 

It is both, LSST is a major astronomical observatory, the impact to LSST would be part of the impact to astronomy. The total impact to astronomy would consist of tallying up the impact to each individual observatories, but so far none of the other observatories have given a quantitative analysis of the impact, so we have nothing to go on for the other cases.

By virtue of very long exposure times, satellites crossing the LSST's image field in a given exposure can be filtered out.

If this is a convoluted way to say impact to LSST is smaller than impact to other observatories, I don't think so, but that doesn't matter. If astronomers think their work is being impacted, they need to use data and numbers to back up the claim, so far they have not done so.

I've noticed that the AAS official statement mentions the natural night sky. That's important.

Actually that part reduced the credibility of the statement significantly. Astronomers are not the guardian of the natural night sky, we certainly didn't elect them to do this, they only represent their trade which is astronomy and should limit their comment to astronomy. They have no right to extend their reach to anything related to natural night sky, you say SpaceX didn't ask you about night sky, well AAS didn't ask me about night sky either.

[Semmel]

su27k, I like your comment very much because it summarizes the situation very well. I work in astronomic instrumentation and if I can find some time in my schedule to do any kind of quantitative analysis of the impact on astronomy, I will do so. However, the topic is quite loaded with opinions and political pitfalls. Therefore, any computation will have to be checked and tripple checked by colleagues. I will have to be very thorough in approach and analysis, which takes time.

Its easy to throw out some back of the envelope calculations, but if you want real numbers that are not pulled out of my backside, its a different story that will take time to complete. Also it requires the support of my institute which is not clear if I get it.

[MaxTeranous]

su27k, I like your comment very much because it summarizes the situation very well. I work in astronomic instrumentation and if I can find some time in my schedule to do any kind of quantitative analysis of the impact on astronomy, I will do so. However, the topic is quite loaded with opinions and political pitfalls. Therefore, any computation will have to be checked and tripple checked by colleagues. I will have to be very thorough in approach and analysis, which takes time.

Its easy to throw out some back of the envelope calculations, but if you want real numbers that are not pulled out of my backside, its a different story that will take time to complete. Also it requires the support of my institute which is not clear if I get it.

Surely if this is going to be such a massive issue to astronomy tho, shouldn’t those institutes should be throwing personnel and funding at it to rapidly complete the analysis? They can then use that quantified data to back their concerns to the respective government agencies.

If they’re not bothered about supporting you or anyone else, clearly it’s not considered that much of an issue after all.

[Robotbeat]

su27k, I like your comment very much because it summarizes the situation very well. I work in astronomic instrumentation and if I can find some time in my schedule to do any kind of quantitative analysis of the impact on astronomy, I will do so. However, the topic is quite loaded with opinions and political pitfalls. Therefore, any computation will have to be checked and tripple checked by colleagues. I will have to be very thorough in approach and analysis, which takes time.

Its easy to throw out some back of the envelope calculations, but if you want real numbers that are not pulled out of my backside, its a different story that will take time to complete. Also it requires the support of my institute which is not clear if I get it.

Surely if this is going to be such a massive issue to astronomy tho, shouldn’t those institutes should be throwing personnel and funding at it to rapidly complete the analysis? They can then use that quantified data to back their concerns to the respective government agencies.

If they’re not bothered about supporting you or anyone else, clearly it’s not considered that much of an issue after all.

Give it time.

On the other hand, this was predictable years actually decades ago. There has been a long time to request funding; it’s just a hot topic now.

[Semmel]

su27k, I like your comment very much because it summarizes the situation very well. I work in astronomic instrumentation and if I can find some time in my schedule to do any kind of quantitative analysis of the impact on astronomy, I will do so. However, the topic is quite loaded with opinions and political pitfalls. Therefore, any computation will have to be checked and tripple checked by colleagues. I will have to be very thorough in approach and analysis, which takes time.

Its easy to throw out some back of the envelope calculations, but if you want real numbers that are not pulled out of my backside, its a different story that will take time to complete. Also it requires the support of my institute which is not clear if I get it.

Surely if this is going to be such a massive issue to astronomy tho, shouldn’t those institutes should be throwing personnel and funding at it to rapidly complete the analysis? They can then use that quantified data to back their concerns to the respective government agencies.

If they’re not bothered about supporting you or anyone else, clearly it’s not considered that much of an issue after all.

Give it time.

On the other hand, this was predictable years actually decades ago. There has been a long time to request funding; it’s just a hot topic now.

The thing is, when considering the normal operation of an observatory, its quite obviously not a big deal, even though it will have an effect. The devil is in making an analysis that quantifies the impact without messing it up. It is easy to forget things. Its easy to get stuff wrong. Usually thats not a big deal in science, we are wrong practically all the time. Thats how science works. The problem begins if the question at hand is politically loaded. Only idiots and/or masochists try to analyse politically loaded questions.

[speedevil]

AURA Statement on the Starlink Constellation of Satellites

. A very conservative upper limit on the number of LSST pixels affected by Starlink satellites is about 0.01%, and quite likely smaller. Therefore, for LSST, even a constellation of about 10,000 Starlink satellites would be a nuisance rather than a real problem.

The bold part is the only quantitative estimate of the negative impact of Starlink to astronomy I can find so far, looks like at least in this case impact is basically non-existent.

The bold part is a quantitative estimate of the negative impact of Starlink to the LSST, not to astronomy.  By virtue of very long exposure times, satellites crossing the LSST's image field in a given exposure can be filtered out.

This is incorrect.
LSST has very short exposures.
It takes two 15s exposures per pointing.
These exposures then do not go into a pile of images, they are then put into what amounts to a database of objects after a very long pipeline to properly categorise image artifacts.

The CCDs in LSST are 56000 pixels across, with a 1/20 radian field of view.
This means that (if overhead), the field of view is 25km. and during one exposure the satellite will move 140km. A starlink satellite will 'always' only affect one frame of two, so will never be picked up as a false object.

The resolution of LSST is (at 500km) 0.5m, though obviously it has a 9m diameter diameter of a point.
Due to a starlink sat being 10m across, it's probably reasonable to assume it wipes out a 20m stripe (40 pixels wide* 16000 pixels/s), if it does not bloom.
The pixel depth before blooming is 175k electrons, or multiplied by the 64K pixels, 10 billion photoelectrons/s from a 60m^2 dish.
Or 150M photoelectrons/s/m^2.
This is 6*10^-11W/m^2.
Or, equivalent to a magnitude 10 star.

That is - if a source of an equivalent brightness is streaked over the LSST, it will not saturate it and have any science impact beyond the tiny fraction of the sky that is its track.
6*10^-11W/m^2 * 500km^2 *6(hemispherical)*60(area of LSST) = 12W that can be radiated by the starlink satelite without causing blooming.

The Starlink sat is reflecting ~10kW of light, so it is probably safe to say that without active measures on starlinks part, it will cause blooming.

I have annoyingly been unable to find the effect of blooming for various magnitude sources over 10.


17:10 details this process, i strongly recommend this talk, and the ones in the 'Mario' series if you are interested in how modern astronomy with piles of data is going to be done. 

[envy887]

It's unclear what this would mean for a 12000 satellites, as the details of their orbits are not known. A rough guess would be to multiply these numbers by a factor of 7 (12000/1600). So around 70 to 100 satellites visible during twilight at any time and any location![/b]

Aren't the orbits listed in the FCC filing? And 80% of the additional satellites would be at 300-350 km where lighting and height above horizon are very different, so scaling from calculations for the 550 km satellites is probably not very useful.

[jee_c2]

I just thought about how to avoid disturbing the astronomical observations by the satellites.
So, the sats are emitting radiation itself, and also they are reflecting certain radiations (most importantly this is sunlight). We would want to minimize these.
If you think about it, this is very much like the problem of hiding a craft (aircraft, or ship), which means the stealth technology. So, the same methods, applying the same design patterns could help (i.e. non reflective coating, flat surfaces, ..)

Also, if we want to protect the surface observations, there is a good chance using the directional property of it. That means, we can use well positioned shield(s) on the sats, which prevents the reflected or the own radiation to ray in the direction of the Earth (in a designed interval of angles).

Probably the solar array is one of the biggest problem, IMO.

I'm interested in, what the real extent of this problem is, and how they could solve it, but - I think - that we will know it only after more satellites will be deployed.

[su27k]

SpaceX lost contact with 3 of the Starlink internet satellites it launched in May, but the company seems pleased with its first batch overall

In addition, SpaceX added that it "continues to monitor the visibility of the satellites as they approach their final orbit" and that they will be measured for their visibility from the ground once there. Those comments are likely meant to address concerns lodged by astronomers about the reflectivity of Starlink spacecraft — and the bright streaks they've caused in telescope images.

"We have also proactively reached out to leading astronomy groups from around the world to discuss the Starlink mission profile, scientifically assess the impacts on astronomy activities and evaluate any helpful mitigations moving forward," the company said in an email.

[eeergo]

Great quantitative simulation:

https://twitter.com/cgbassa/status/1185498417193275393

[Stan-1967]

Do professional observatories Schedule serious observations in the twilight hours of each night? Furthermore, how many of those observations at twilight are at 30° above the horizon or lower?