Impacts of Large Satellite Constellations on Astronomy

[CJ]

I live in a fairly dark-sky rural area, and at an altitude of over 7000 ft. I also have pretty good eyesight. I love the spectacular night sky here, it's a big part of why I live where I do. I too was concerned about Starlink and similar proposed large constellations, thinking that they'd be an eyesore in the evening sky (though obviously not for long after sunset, due to being in LEO and me not being at high latitude).

So, when the first Starlink launched, I decided to have a look for myself and see how bad they'd be. I used the starlink spotting there on this board, and also sites like Heavens Above to find visible passes of the Starlink train. I tried again after the second launch, always with superb observing conditions. I'm still trying. I think I saw one, briefly and faintly, with binoculars. Still not sure. And that's for a train, which is a temporary formation. I'm definitely no longer worried about my night sky, not from this anyway. 

As for visible spectrum astronomy, I can see this being an issue - but only when the sats are in sun and the ground is in darkness in the direction of viewing. One option might be to invert the low elevation viewing direction; right after sunset, point east. Right before dawn, point west. That would minimize the affected time.

My current take; this is a real issue, because it may reduce the viewing hours available by non-trivial amount. However, it's also being massively overblown IMHO - it's not as if the sats will be visible all night long (well, except at very high latitudes near summer solstice, anyway). 

I do wonder if the sat makers could easily and cheaply mitigate the issue somewhat, via adding a little dull black paint to shiny areas of the sats (excluding on surfaces where it would impair function, of course). 

   

[Star One]

Just to prove regulatory authorities don’t always get things right, including the FCC you only have to look at this decision.

https://www.nationalgeographic.com/science/2019/11/will-5g-wreck-out-weather-forecasts/

[envy887]

It is not sure this constellations will blockade astronomers sky. The problem is that nobody has study properly this potential impact and how it will affect ground astronomy (current and future). It is wrong to do this things in that way.

Maybe if astronomers calculated how much of their data will actually be affected, more people would care about their concerns. The only numbers I've seen, regarding LSST, suggest that less than 1% of their data will be affected by the 12,000 satellite constellation.

[su27k]

It is not sure this constellations will blockade astronomers sky. The problem is that nobody has study properly this potential impact and how it will affect ground astronomy (current and future). It is wrong to do this things in that way.

Only astronomers have the expertise to do this study, and they had ample time to do this since these constellations were proposed in 2015.

[sebk]

And again, we already have LEO constellations in orbit (e.g. Iridium).
Once more: other than "there are more", what is different with Starlink (and OneWeb, etc) that requires special mitigations, while existing constellations (and other satellites and other objects like spent stages, dead satellites, and general debris) do not? And if there is no difference beyond quantity, why are whatever current mitigations for satellite passes over ground-based telescopes viable for the current several hundreds to thousands of objects but not for additional objects?

1) they are not radio emitting.
2) the important quantity is not only numbers, but apparent magnitude.

1) Iridium is strongly radio emitting. All live sats are at radio emitting just for telementry, but comm stats like Iridium emit widely and strongly.
2) Prev generation Iridium had flares up to -8mag or so...

[sebk]

There are claims that an object of 5 mag would damage observations (especially the concern is about wide field observations).

But sats are not stationary objects. Typical observations take multi-second exposures (dozens of seconds usually). Sats at 20° above the horizon would move one degree in no less than 4s (in the worst case when the sat is moving straight "towards" or "awa" to/from the observer). Wide field in astronomy is usually about "looking" at 3° circle or so, so ~12s to move across the field. If the observation was very low res at ~1M pixels it would be 1000 pixel path crossed in 12s, so even assuming light bleeding across 10 pixels diameter (5 pixel radius to one sigma decrease; the resolution would be bad at 36") such low res pixels each would get about 1/150th the exposure of stationary object. If the resolution is higher then we get more pixels on the path, but also more (but smaller) pixels the light bleeds into, so it's about the same.

So the the exposure intensity of 5th magnitude sat at 12s exposure would be like ~10.5mag stationary object. There is no square degree of the sky without multiple mag 10.5 or brighter objects. And 10.5 mag imprint is in the slowest movement case (20°, straight towards or away from the obsever). If the sat is transverese or close to zenith its moving about 3× faster so the effect is slightly more than 1mag weaker.

If the exposure is longer, like 300s, then the sat would leave imprints like 14-15mag stationary exposure (depending on angle and trajectory).

[b0objunior]

It is not sure this constellations will blockade astronomers sky. The problem is that nobody has study properly this potential impact and how it will affect ground astronomy (current and future). It is wrong to do this things in that way.

Only astronomers have the expertise to do this study, and they had ample time to do this since these constellations were proposed in 2015.

Ha yes, it's people who drink water should do the study as to why people shouldn't poison the well, not the ones dopping lead into it.

[pochimax]

There are claims that an object of 5 mag would damage observations (especially the concern is about wide field observations).

But sats are not stationary objects. Typical observations take multi-second exposures (dozens of seconds usually). Sats at 20° above the horizon would move one degree in no less than 4s (in the worst case when the sat is moving straight "towards" or "awa" to/from the observer). Wide field in astronomy is usually about "looking" at 3° circle or so, so ~12s to move across the field. If the observation was very low res at ~1M pixels it would be 1000 pixel path crossed in 12s, so even assuming light bleeding across 10 pixels diameter (5 pixel radius to one sigma decrease; the resolution would be bad at 36") such low res pixels each would get about 1/150th the exposure of stationary object. If the resolution is higher then we get more pixels on the path, but also more (but smaller) pixels the light bleeds into, so it's about the same.

So the the exposure intensity of 5th magnitude sat at 12s exposure would be like ~10.5mag stationary object. There is no square degree of the sky without multiple mag 10.5 or brighter objects. And 10.5 mag imprint is in the slowest movement case (20°, straight towards or away from the obsever). If the sat is transverese or close to zenith its moving about 3× faster so the effect is slightly more than 1mag weaker.

If the exposure is longer, like 300s, then the sat would leave imprints like 14-15mag stationary exposure (depending on angle and trajectory).

Completily nonsense

[envy887]

There are claims that an object of 5 mag would damage observations (especially the concern is about wide field observations).

But sats are not stationary objects. Typical observations take multi-second exposures (dozens of seconds usually). Sats at 20° above the horizon would move one degree in no less than 4s (in the worst case when the sat is moving straight "towards" or "awa" to/from the observer). Wide field in astronomy is usually about "looking" at 3° circle or so, so ~12s to move across the field. If the observation was very low res at ~1M pixels it would be 1000 pixel path crossed in 12s, so even assuming light bleeding across 10 pixels diameter (5 pixel radius to one sigma decrease; the resolution would be bad at 36") such low res pixels each would get about 1/150th the exposure of stationary object. If the resolution is higher then we get more pixels on the path, but also more (but smaller) pixels the light bleeds into, so it's about the same.

So the the exposure intensity of 5th magnitude sat at 12s exposure would be like ~10.5mag stationary object. There is no square degree of the sky without multiple mag 10.5 or brighter objects. And 10.5 mag imprint is in the slowest movement case (20°, straight towards or away from the obsever). If the sat is transverese or close to zenith its moving about 3× faster so the effect is slightly more than 1mag weaker.

If the exposure is longer, like 300s, then the sat would leave imprints like 14-15mag stationary exposure (depending on angle and trajectory).

Completily nonsense

So the object tracing across multiple pixels is still able to drop as many photons on each one as if it were stationary for the full exposure?

[envy887]

The lower albedo sats apparently haven't launched yet.

https://twitter.com/jeff_foust/status/1203318574376529920

[guckyfan]

So all telescopes on earth go through clean room maintenance with maintenance precision after their initial construction? By which I mean, the telescopes that are so much cheaper than their in-space counterparts that were now doomed according to the post I responded to.

Yes, they are. Check it on the net.

Here a picture of a complex instrument on one of ESO's VLT. It is a very complex instrument. I disagree with your comment intention of " much cheaper than their in-space counterparts". This instruments aren' t cheap. They are expensive. The problem is that space counterpart will be incredible expensive (compared to ground instruments)

¿could you imagine an astronaut trying to fix something on this instrument?

I had to check. This is not an optical instrument. It observes the k-band. How does this fit into a discussion of optical astronomy?

https://www.eso.org/sci/facilities/develop/instruments/kmos.html

[ThomasGadd]

Another spacenews article.   

https://spacenews.com/spacex-working-on-fix-for-starlink-satellites-so-they-dont-disrupt-astronomy/

[ilando]

I had to check. This is not an optical instrument. It observes the k-band. How does this fit into a discussion of optical astronomy?

https://www.eso.org/sci/facilities/develop/instruments/kmos.html

I had to double check. It is indeed an optical instrument of course. A quick glance at the page you linked confirms this.

[guckyfan]

I had to check. This is not an optical instrument. It observes the k-band. How does this fit into a discussion of optical astronomy?

https://www.eso.org/sci/facilities/develop/instruments/kmos.html

I had to double check. It is indeed an optical instrument of course. A quick glance at the page you linked confirms this.

The title says k-band. Red shift applies to microwave as well. In the text it says it will be combined with infrared.

[ilando]

"The patrol field of the pickoffs is 7.2 arcmin in diameter, which is the diameter of the unvignetted field at the VLT Nasmyth focus, thus minimising the thermal background in the K-band."

You said "This is not an optical instrument."
It clearly is.

[Yellowstone10]

Ha yes, it's people who drink water should do the study as to why people shouldn't poison the well, not the ones dopping lead into it.

That metaphor doesn't really work. It suggests a situation in which everyone was cooperatively using a common resource, until one group decided to monopolize it in a way that excludes everyone else. But what we've got is one group (astronomers) using a resource, and when others (anyone wanting to expand humankind's presence in space) want to use the resource as well, the first group protests, because their use of the resource is most effective when they don't share.

To use the well analogy - think hydrogeologists studying a natural well, and then when people want to use the well for drinking water too, the scientists argue that sharing the well will interrupt their research.

[pochimax]

There are claims that an object of 5 mag would damage observations (especially the concern is about wide field observations).

But sats are not stationary objects. Typical observations take multi-second exposures (dozens of seconds usually). Sats at 20° above the horizon would move one degree in no less than 4s (in the worst case when the sat is moving straight "towards" or "awa" to/from the observer). Wide field in astronomy is usually about "looking" at 3° circle or so, so ~12s to move across the field. If the observation was very low res at ~1M pixels it would be 1000 pixel path crossed in 12s, so even assuming light bleeding across 10 pixels diameter (5 pixel radius to one sigma decrease; the resolution would be bad at 36") such low res pixels each would get about 1/150th the exposure of stationary object. If the resolution is higher then we get more pixels on the path, but also more (but smaller) pixels the light bleeds into, so it's about the same.

So the the exposure intensity of 5th magnitude sat at 12s exposure would be like ~10.5mag stationary object. There is no square degree of the sky without multiple mag 10.5 or brighter objects. And 10.5 mag imprint is in the slowest movement case (20°, straight towards or away from the obsever). If the sat is transverese or close to zenith its moving about 3× faster so the effect is slightly more than 1mag weaker.

If the exposure is longer, like 300s, then the sat would leave imprints like 14-15mag stationary exposure (depending on angle and trajectory).

Completily nonsense

So the object tracing across multiple pixels is still able to drop as many photons on each one as if it were stationary for the full exposure?

Obviously not.

What does that have to do with the nonsense of the post I quoted?? Have you read it?

[pochimax]

So all telescopes on earth go through clean room maintenance with maintenance precision after their initial construction? By which I mean, the telescopes that are so much cheaper than their in-space counterparts that were now doomed according to the post I responded to.

Yes, they are. Check it on the net.

Here a picture of a complex instrument on one of ESO's VLT. It is a very complex instrument. I disagree with your comment intention of " much cheaper than their in-space counterparts". This instruments aren' t cheap. They are expensive. The problem is that space counterpart will be incredible expensive (compared to ground instruments)

¿could you imagine an astronaut trying to fix something on this instrument?

I had to check. This is not an optical instrument. It observes the k-band. How does this fit into a discussion of optical astronomy?

https://www.eso.org/sci/facilities/develop/instruments/kmos.html

And?

It doesn' t matter for the discussion at that moment at all.

It was only an example of a very complex instrument in a ground telescope. You could easily find a counterpart of an optical spectrum instrument, looking for pictures on the net.

[pochimax]

And again, we already have LEO constellations in orbit (e.g. Iridium).
Once more: other than "there are more", what is different with Starlink (and OneWeb, etc) that requires special mitigations, while existing constellations (and other satellites and other objects like spent stages, dead satellites, and general debris) do not? And if there is no difference beyond quantity, why are whatever current mitigations for satellite passes over ground-based telescopes viable for the current several hundreds to thousands of objects but not for additional objects?

1) they are not radio emitting.
2) the important quantity is not only numbers, but apparent magnitude.

1) Iridium is strongly radio emitting. All live sats are at radio emitting just for telementry, but comm stats like Iridium emit widely and strongly.
2) Prev generation Iridium had flares up to -8mag or so...

You can't compare a hundred satellite constellation problem with a thousands of satellites constellation/s.

Radio astronomy NOW have a problem with this kind of satellites, but they can deal with it, because low numbers . But, what if you  multiply the problem 1000x ? It is not the same, obviously.

[pochimax]

https://aas.org/posts/advocacy/2019/12/aas-works-mitigate-impact-satellite-constellations-ground-based-observing

The first launch of SpaceX's Starlink satellite constellation was on 23 May 2019. The response from our community was loud enough that SpaceX reached out to the AAS looking to establish a line of communication. Since optical/infrared interference doesn’t have a statutory or regulatory framework like radio interference, they hadn’t had any interactions with that part of our community.

The AAS Public Policy staff worked with the AAS Committee on Light Pollution, Radio Interference, and Space Debris to assemble a working group that would be the main channel of communication between the astronomical scientific community and SpaceX.

The first telecon between SpaceX and our working group was on 6 June. There have been eight telecons so far, with the last one having been on 25 November, two weeks after the second Starlink launch. The members of our working group have been making other efforts to get on top of this issue. We have met with other satellite industry players, House Science Committee staff, NSF’s Spectrum Management staff, Space Commerce, and the space law community. We also held an initial status update telecon for major US observatories and the European Southern Observatory (ESO) back in October.

Things are moving in a hopeful direction after our last two telecons. SpaceX is willing to test coatings to see if that helps bring down the brightness. Despite all the complexities of how our community makes O/IR observations, we are working to see if we can develop a brightness level for them to aim at, and we are conducting a survey of research observatories to gather this information. We also need simulations, as so far only a few people are modeling the impacts to observatories. SpaceX is also working on their own simulations to help observatories avoid Starlink. We have discussed with SpaceX the best way to disseminate their launch schedules to observatories for avoidance purposes.

SpaceX plans to have 1,584 Starlink satellites in orbit by the end of 2020. All of our options for impact mitigation will require iterative processes. Until we have collected the survey data, we and SpaceX will proceed as if satisfying the Large Synoptic Survey Telescope's needs is the high bar to aim for.

The goal of Starlink is to provide worldwide internet service, an aspiration we do not want to impede, but this requires one to two orders of magnitude more low Earth orbiting satellites (LEOs) than currently exist. We do not want to give up access to optical observations from the ground. Our group’s task is to find a path forward that accommodates both uses of the sky. If you’d like to hear more about our efforts, we have a Special Session planned for AAS 235 in Honolulu, Hawai‛i:

Challenges to Astronomy from Satellites
Wednesday, 8 January
10:00 am – 11:30 am
Ballroom AB, Hawaii Convention Center