Re: Starlink train L15 suddenly becomes visible

From: Richard Cole via Seesat-l <seesat-l_at_satobs.org>
Date: Mon, 14 Dec 2020 18:51:34 +0000
Tom,

Some months ago SpaceX changed the orientation of most Starlinks in low 
orbit (below 550km) to 'edge-on' mode which meant their solarpanels were 
placed edge-on to the Sun when the spacecraft were visible from the 
ground and the Starlink is dark. However, this mode is only entered some 
time after launch (and from my own observations that can now be many 
weeks after launch - SpaceX seem more relaxed than before).

Before the point in time they move to this edge-on mode they are in the 
so called 'open-book' mode with the axis through the panels aligned to 
the velocity vector. The spacecraft is rotated around the velocity 
vector axis so the maximum sunlight falls on the panel face. This 
rotation angle is being changed all the time so this condition is 
maintained and the batteries are charged.

It just so happens that when you saw (from Waterloo) the L15 Starlinks 
entering eclipse they were moving almost _exactly_ away from the 
Sun-direction (in the WSW) and since the Sun was below the horizontal 
(at the spacecraft) that meant the panels were pointing almost directly 
towards the ground (and therefore towards you). So you were seeing the 
full sun-illuminated face of the solar panel and the Starlinks were very 
bright. I saw this phenomenon a month or so ago with Starlinks from a 
previous launch and they were really very bright (mag 0 at one point).

If the Starlinks are not directly moving towards or away from the Sun 
then the panels are pointing towards the Sun (which is left of right of 
the spacecraft track) and not towards the ground and the Starlinks can 
be much fainter.

Sorry if this wordy explanation isn't clear, there are some digrams of 
mine at 
https://sattrackcam.blogspot.com/2020/05/guest-post-modelling-of-starlink-trail.html 
that might assist.

regards

Richard

On 14/12/2020 01:50, Tom Wagner via Seesat-l wrote:
> 
> 
> This may have been asked before.
> 
> I have found that seeing the Starlink trains – even a couple weeks after launch – has not been easy. Since they have sunshields I find them very faint and in fact, once, even when using 7 x 35 binoculars, I wasn’t able to see them between clouds, and that was at a high altitude.
> 
> Now in the first week of this December suddenly people around the US are seeing the last launch and thinking they are UFOs. I saw L15 myself on December 5 and it was easy to see from when it came over my house near Lyra all the way to where they entered the earth’s shadow in the NE.  I estimated their brightness as being about a magnitude 3, close to what HA predicted at that time.
> 
> I’m wondering, are they more visible in the US now because of the sun’s angle this time of year? They did not appear to be flaring.
> 
> Thanks,
> 
> Tom Wagner
> Waterloo, Iowa USA
> 
> 
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> 
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Received on Mon Dec 14 2020 - 12:52:44 UTC

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