Re: Modeling Starlink magnitudes in a simulation

From: George Roberts via Seesat-l <seesat-l_at_satobs.org>
Date: Wed, 3 Jun 2020 11:44:16 -0400
Max, I believe that model assumes the satellite is a flat-painted sphere 
(gray or white but flat paint).  "flat" here refers to the paint 
properties.  Also known as "matte".

This works pretty well for cylindrical rocket bodies but not so well for 
starlink's which have basically only 2 flat surfaces at 2 different angles.

There is talk about having the solar panels "knife edge" to the sun at 
sunrise and sunset.  I don't think that will happen as this reduces 
electricity production and complicates maneuvers.  More likely the solar 
panel will be pointed away from the earth and knife edge towards 
direction of travel (to reduce drag).  The rest of the satellie is also 
flat and parallel to the earth surface (see photo with satellite in 
"shark-fin" mode - "open book" is only for orbit raising mode).

https://phys.org/news/2020-05-spacex-theyre-starlink-satellites-visible.html

Modeling these 2 surfaces and knowing where an observer is on earth and 
where the sun is would give much more accurate predictions for 
brightness of starlink.

- George

On 6/3/20 10:42 AM, Max Hartshorn via Seesat-l wrote:
> Thank you all for the great tips and feedback! I have a much better idea
> now how to go about this, and the challenges involved. I will go ahead and
> take a stab at this, with the knowledge that a truly accurate visualization
> of the planned Starlink constellation at this point is essentially
> impossible given the number of unknowns. I will post the results here for
> feedback before posting anywhere else.
>
> Ted, the tool I am using to visualize satellites, Stellarium, computes
> magnitude from the quicksat.mag database, which defines standard magnitude
> as 1000km range at 50% illuminated. I there some formula required to
> convert the observations that you attached, which are at various phase
> angles, to a 50% illuminated value?
>
> On Tue, Jun 2, 2020 at 2:39 PM Richard Cole <richardc_at_recole.plus.com>
> wrote:
>
>> Max,
>>
>> 1. I did this simulation of a completed 1440 satellite first shell
>> constellation some months ago. I tried to make the final sky simulation
>> segment representative of standard (non-Darksat) Starlinks, that is just
>> visible to the naked eye. They are quite hard to see in the video (which
>> was the idea) (done with Heavensat).
>>
>> https://vimeo.com/411339908
>>
>> 2. Trying to simulate the brightness of spacecraft on the way up (the
>> Trains in SpaceX's termed 'open-book mode') will need a lot of work to
>> understand how the spacecraft are flown and hence how they appear to an
>> observer. In any case SpaceX are now using Knife-edge mode which means
>> the Trains are now much fainter and not spectacular. SpaceX has stated
>> that the first few days of each mission will be bright, but then the
>> spacecraft will be put into the darker knife-edge mode. My suggestion
>> would be to stick to simulation of the deployed Starlinks.
>>
>> 3. The Starlink constellation design is changing all the time. A new
>> application for a 30000 spacecraft Gen2 constellation was made a couple
>> of weeks ago. How that matches to the current constellation now in
>> build, or the one originally proposed, or the modification to that
>> proposed a while ago, is anyone's guess. Or whether all the current
>> plans will be replaced with new ones before they are implemented.
>>
>> Gen 2 application
>>
>> https://licensing.fcc.gov/cgi-bin/ws.exe/prod/ib/forms/reports/swr031b.hts?q_set=V_SITE_ANTENNA_FREQ.file_numberC/File+Number/%3D/SATLOA2020052600055&prepare=&column=V_SITE_ANTENNA_FREQ.file_numberC/File+Number
>>
>> and a simulation https://vimeo.com/424500440
>>
>> Good luck with the project. I will be interested in the result.
>>
>> regards
>>
>> Richard Cole
>>
>>
>> On 02/06/2020 14:42, Max Hartshorn via Seesat-l wrote:
>>> Hi All,
>>>
>>> I'm new to this list and new to satellite observation. My name is Max
>>> Hartshorn and I'm a computer programmer and data journalist based in
>>> Toronto, Canada. I became interested in Starlink after I inadvertently
>>> witnessed the initial load shortly after the launch last May. They were
>> by
>>> far the brightest objects in the sky...though I understand their apparent
>>> magnitudes will have decreased considerably once they reached their final
>>> orbit.
>>>
>>> What I'd like to do is create a *responsible* and *non alarmist*
>>> visualization of what the night sky *could* look like when 12,000
>> Starlink
>>> satellites are up and running. As far as I know such a simulation does
>> not
>>> exist.
>>>
>>> I've been playing around with Stellarium and TLEs and I can see that it's
>>> possible to generate a TLE file for 12,000 satellites at roughly the
>>> configuration proposed by Starlink, and model those orbits in Stellarium.
>>> But the big open question is around magnitudes.
>>>
>>> I've been looking through the archives here and I've seen a range of
>>> apparent magnitude observations, anywhere from 2 to 9. Additionally
>>> Starlink is iterating the design of their satellites to minimize
>>> reflectivity.
>>>
>>> The threshold that's most interesting to me is the 6.5 threshold for
>> naked
>>> eye observation. If the satellites (particularly those in the lower
>> orbital
>>> shells) are below that threshold, they could potentially impact how the
>>> general public views the night sky.
>>>
>>> Is there any agreed upon estimate for the apparent magnitude of the
>>> Starlink satellites currently in orbit? Do we just not know yet? Are
>> there
>>> any responsible methods for modeling / estimating the magnitude of the
>>> remaining satellites?
>>>
>>> Sorry for the long email. I figure if anybody would know the answers to
>>> these questions it would be you folks :)
>>>
>>> Thanks,
>>> Max
>>> _______________________________________________
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>>> http://mailman.satobs.org/mailman/listinfo/seesat-l
>>>
>> --
>> mob:  0771 858 8940
>>
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Received on Wed Jun 03 2020 - 10:45:19 UTC

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