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djswan2002's picture
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Project idea

Hello,

Just floating an idea - 

How about setting up a prospective study to quantitatively assess the impact of the coming onslaught of satellite constellations on our observing? (Or maybe we don't think, say amateur imaging, is really going to be affected in a major way in the near future?)

David

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Summer time imaging

Well, as the satellites are not illuminated by the sun after twilight in the winter, the winter may become the best time for long exposure wide angle imaging. Mid-summer is going to be horrific if thousands of these things go up. 

As I recall, one of the Musk sats has a new paintjob that is supposed to be lower albedo. Does it look obviously dimmer? Has anyone observed it yet? My best guess is that if they will have managed an attentuation of the order of 2-2.25 mags. So they will still be bright enough to ruin almost any telescopic image. 

The ordure is really going to encounter the ventilation system when they start failing, attitude control is lost and the tumbling starts. Some of the flares are going to be impressive. But hey, its okay, someone will get rich on the back of this.

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Some random scribbles on Starlink

djswan2002,  I too would welcome an in-depth study into the impact of Starlink et al as it’s something that I certainly find concerning.

I’ve done a little digging around the internet and what I’ve found doesn’t look too good, I’ve tried to summarise my thoughts here as best as possible. This is by no means a study into Starlink, at best it’s a few random scribbles on the back of an envelope by someone who considers himself as a mere star gazer and no mathematician and certainly not an astronomer, but it’s food for thought, even if it may not stand up to scrutiny.

The number of proposed satellites

Starlink    42,000     (12,000 approved, paperwork submitted to International Telecommunication Union for 30,000 more)

Amazon     3,000

OneWeb      650     (possibly increasing to 2000)

TelSat LEO    300

Hongyun       320     (altitude 1,100km)

 

Total        46,270  New Satellites

 

Others who have proposed constellations but so far have no planed launches

Boeing        1,400

Samsung    4,600

 

The total number of new satellites then stands at a whopping 46,270 up to a possible 53,620 in the next decade. That is in addition to nearly 2,000 current operational satellites and 20,000 bits of space debris of which around 1500 are 100kg or above.

So what impact is this likely to have?

** Note Xilman pointed out a pretty dumb mistake I made when doing the following calculations, he quite correctly pointed out that I should have used steradians to work out the total number of square degrees, doing so gives a total of 41,253 not  the erroneous figure of 129600 (now removed) that I initially came up with. The corrected maths follows  **

So, to calculate the total square degrees that would be 360 / (2 x pi) = 57.3 (there abouts) and then (4 x pi) x 57.3^ = 41253 square degrees. (always the same value for any size of sphere).

That would then give us a concentration of  46,270 satellites divided across 41,270 square degrees 

  46,270 / 41,253 = 1.12 satellites per one square degree

So, if the moon covers an area of 0.2 square degrees (if memory serves me correctly) that equates roughly to one satellite for each area of the sky equal to five times the area of the moon based on the lower number of satellites or 1.38 satellites in the same area if using the higher number of 57,120. That seems quite a lot to me!

Starlink / Space x have said they will look at measures to reduce the albedo of their satellites, this may help, however some are suggesting that the solar panel cannot be altered and it’s the most reflective part. Additionally a few have mentioned on various forums that the combined effect of so many objects in or close to near earth orbits is going to cause a not insignificant occultation issue for DSO observations in particular asteroid hunting using the blink comparison technique.

I’ve only really concentrated on the increase in numbers of objects in NEO , there is of course other issues like the amount of RF these satellites will emit and the impact of the satellite to satellite links, which I recall reading somewhere were going to be done optically (is that some sort of laser or IR link perhaps), nor have I went into detail on the size of the satellites, indeed, information on the physical size of the satellites seems very sparse, an estimate made by one person on reddit puts the size at around 1.1m x 2.4m for the satellite body not including the solar panel. Cees Bassa from the Netherlands Institute for Radio Astronomy, calculated that up to 140 of the starlink mega constellation satellites could be visible at any one time if all the planned satellites launch (Forbes.com article).

Another article from Space.com highlights the brightness of these new satellites -  

[Patrick Seitzer, an astronomy professor emeritus at the University of Michigan, said Wednesday (Jan. 8) during a special news conference at the 235th meeting of the American Astronomical Society (AAS) called "Astronomy Confronts Satellite Constellations." 

"We knew these tens of thousands[-strong] megaconstellations were coming, but based on the sizes and shapes of things currently in orbit, I thought maybe 8th or 9 magnitude," Seitzer added. "We were not expecting 2nd or 3rd magnitude in the parking orbits, and we were certainly not expecting 4th to 5th magnitudes in the [operational] orbits."]

 

In conclusion, will this amount to a change in astronomy as we know it? – Personally I’d say yes, but I'm not 100% sure, it may even render backyard astrophotography almost impossible, however there are many that say otherwise and even those who say it will have an impact on astronomy seem to be taking a wait and see approach. Again, speaking personally, I find the ‘wait and see’ approach as frankly bazar. Are we going to be in a position ten or twelve years from now when the astronomical community look up and say, ‘we can now say for certain this is having a big impact on us, would you mind taking your $30 billion per year earning satellites down please so we can do astronomy again?’ I can imagine the answer to that question would be short and to the point.

Smoking probably isn’t bad for you….

Nah, CFC’s couldn’t be damaging the ozone layer….

Dumping millions of tons of plastic every year is fine, it’s not an issue….

Putting tens of thousands of satellites in orbit around our planet is not going to be a problem………

Err, Houston…. We may have a problem!

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Devil's Advocate

I am going to act as Devil's advocate because someone should do so.  The very phrase "Devil's advocate" should indicate that my personal views are not necessarily in accordance with what I espouse below and in subsequent posts.

First, 4pi steradians is equal to 41,253 square degrees.  We are already down by a factor of pi ( about 3.14) from your estimate.

Secondly. not all astronomers, professional and amateurs, are wide-field imagers.  A good fraction of us perform precision astrometry and/or photometry.  As long as any satellite trails (or cosmic ray hits for that matter) do not intrude on the object or its immediate neighbourhood, our work is completely unaffected,

More Pollyannish sentiments may appear in due course.  This will have to suffice for the time being, not least because dinner is now being served.

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Omission

Spectrosopy is as unaffected, no more, no less, than photometry and astrometry.

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Thank you Xilman

Thanks Paul,

I see the error of my ways! Yes I should have used steradians.

Also, I want to point out that although it may seem I'm biased aginst Starlink et al, I'm not. With thirity plus years in the broadcast engineering and audio visual events sectors I've used more than my fair share of satellite links and I've no doubt (love them or loathe them) I'll probably end up using one or more of the new systems. My concern is that there seems to be a lack of real hard (non biased, non emotional) facts out there on which any of us can make a real judgement. On one side there are those going.... 'Nope, nothing to see here, won't impact us at all...' and then on the other side.... 'It's the end of civilisation as we know it, we'll never see the stars again!' Now I suspect that the big observatories will come up with a software fix in their image processing and likewise those who use stacking will delete all the frames that have been impacted before processing, so there's work-arounds for both. But what about the guy in between (like me) who's a bit old school and just likes to look up at the stars, take some long(ish) exposures from time to time, maybe use some blink comparison looking for DSO's and have no desire to spend lots of time processing images. It's a big enough struggle to get time for the hobby as it is, so to have exposures 'photobombed' by satellites continuously would be soul destroying.

Anyway, here's the revised maths.

So, that would be 360 / (2 x pi) = 57.3 (there abouts) and then (4 x pi) x 57.3^ = 41253 square degrees as you quite rightly point out.

That would then give us a concentration of  46,270 satellites divided across 41,270 square degrees 

  46,270 / 41,253 = 1.12 satellites per one square degree

So, if the moon covers an area of 0.2 square degrees (if memory serves me correctly) that equates roughly to one satellite for each area of the sky equal to five times the area of the moon based on the lower number of satellites or 1.38 satellites in the same area if using the higher number of 57,120.

Is my maths correct?? That seems like an awfully high figure to me.

I will and do freely admit to being purely a stargazer at best so at best my calculations are nothing more than a laymans scribbles on the back of an envelope at best. I do fear though that  the whole [subject, debate, discussion or whatever the current comments around the globe may be regarded as] is simply becoming lots and lots of peoples opinions and hard scientific data is proving very difficult to come by. In the meantime Starlink et al will continue to launch more and more satellites into orbit without anyone being able to conclusively prove if they will or will not be a problem. So, like David Swan (op) I'm curious to see if there is a study anywhere and if not it would be great to see someone pick it up as a project and run a proper in-depth impact study.

Thanks again to Xilman for pointing out the flaw in my initial calculations.

It's all way above my head..... in more ways than one.  :)

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Devil's Advocate

I think that post can be counted as a success and that my client, often known as The Great Deceiver, will be well pleased.

You appear to have been led to believe that a reduction by a factor of pi in the number of degrees in the complete sky is an improvement. In terms of the average number of satellites per square degree, however ...

;-)

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I read the post wrong first

I read the post wrong first time round, I was eating my dinner at the time! lol I went back later re-read and did my maths correctly this time ( I think) :)

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Spectroscopy

The potential effect on spectroscopy is an interesting one as unlike photometry where trails will be obvious in the image, the cumulative contamination from the trails briefly crossing the slit during say a 20 min exposure, either within the binned or background subtracted regions may not be so obvious.

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Spectroscopy

Good point.

Presumably one could monitor the field and avoid taking data during the satellite pass. Could be an interesting exercise writing software for motion detection in the autoguider camera.

How do you deal with satellite trails now?

Depending on whether I am doing photometry or imaging (which includes astrometry for present purposes) I either discard the sub before average-stacking or rely on median-stacking to discard the satellite for me.  In either case, such concerns are of interest only when the satellite passes inconveniently close to the objects of interest, otherwise it is just ignored.

There again, I take as many 30 to 60 second subs as are needed to reach a satisfactory SNR (which depends on sky brightness, for instance) and then move on to another target. A cheap and simple way of optimizing the productivity of telescope time. Vary rarely does a single exposure exceed a couple of minutes.

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spectroscopy star trails

I don't do anything currently. I visually examine each exposure and cannot recall seeing anything that I could put down to a satellite. The satellite will not spend long in the slit though so the contribution could be too small to be obvious, just contributing to the uncertainty. They would be more likely to appear in the wider sky background subtraction zones so hopefully the median averaging across the zone deals with them there.

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Lots of inages

I take nearly 2000 10s slitless images a night and currently very few show a satellite or meteor trail. I hope it stays like that.

Regards Andrew 

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Evidence.

I made the claim As long as any satellite trails (or cosmic ray hits for that matter) do not intrude on the object or its immediate neighbourhood, our work is completely unaffected. Here is some supporting evidence which turned up quite by chance.

Below is an image from my work on U Leo and is the average stack of 32 exposures each of 30 seconds duration, two of which caught a very bright satellite in transit. The gap in the trail shows the movement during period the CCD was downloading its data between successive images. Even when diluted 31-fold the trail is still very obvious. U Leo (the central marked star just to the right of the trail) and it comparison stars are identified; none lie anywhere near the trail so photometry is unaffected. The VS is measured to be V=17.52 +/- 0.05 at 2020-01-21T00:30

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interesting article

Àn interesting article on the BBC Website from December

https://www.bbc.co.uk/news/science-environment-50870117

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Of no great importance ...

I am now at the telescope taking a long series of exposures and a satellite or meteor just went through a frame.  Very faint.  Stars down to 17th mag are easily visible but the trail only just shows up above the sky noise.  Guess 15th or so?  It is going to be completely invisible in the final stack.

Not sure how relevant this is to the current discussion but it shows that we don´t need Starlink to be able to pick up the present vermin of the skies.

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Debris

Last year I was part of a team that did some work on debris in the GEO belt. Using the INT we were still spotting debris objects down to mag 20/21. It didnt look like the population was tailing off even then. But without being allocated time on a bigger scope its hard to know.

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Lots of junk but a really nice telescope

Hi Grant, yes there's an awful lot of 'junk' up there, thankfully it doesn't seem to cause much of a problem, but add another 50,000 satellites and who knows. They are relatively small though, so the impact may be minimal especially if 1130 is a success and the albedo of future satellites is reduced. It will be interesting to see what the results of the trial are.

Wouldn't mind some time on the INT myself never mind anything larger, alas the impact of work and time precludes any such venture for the time being, so I'm stuck in the 'back yard' for now or at least when sky and time permits.

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Darksat

If anyone fancies having a look to see if the new/improved paint job on one of the Starlink satellite has had a good effect, then have a look at Starlink-1130. If its worked well, then we should see an obviously dimmer satellite in the train. TLEs are on Celestrak as "supplemental".

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Worth a look at these perhaps

A fellow member of the IAA drew my attention to this:

  https://astronomersappeal.wordpress.com

I haven't looked through all the sources and links mentioned yet though.

I also see that the IDA have an article published in December on the subject of mega constellations as well

https://www.darksky.org/why-do-mega-constellations-matter-to-the-dark-sk...

Although I am still attempting to stay neutral and open minded, I am gradually growing more concerned.

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Darksat observation

This makes interesting reading.... someone has imaged it.

https://twitter.com/cgbassa/status/1217907157900976129