Starlink design from recent public images

From: Richard Cole via Seesat-l <seesat-l_at_satobs.org>
Date: Thu, 11 Jun 2020 12:25:20 +0000
Some of you will have seen the SpaceX launch video showing deployment of 
the Falcon-9 fairing. It is believed this was from the most recent 
launch, which was at night.

https://www.youtube.com/watch?v=aKWio4zHShM&feature=youtu.be

I have extracted a frame that shows the antenna faces of the uppermost 
two Starlinks in the stack.

https://recole.org.uk/starlink/launch-extract.jpg

I have been looking at this for some time and have come to a couple of 
conclusions:

1. The shape of the baseplate and arrangement of the antennas is as per 
the VisorSat diagram on the SpaceX website. There are other diagrams on 
that site which are quite different in shape and antenna arrangement 
(e.g. the Darksat one).

https://www.spacex.com/static/images/updates/visorsat.png

https://www.spacex.com/static/images/updates/darksat.png

2. The four antenna panels (plus one other panel of unknown purpose) are 
very white. Their brown tint in the images may be due to the colour of 
the fairing. Note there is a lamp installed on the upper surface of each 
Starlink visible, for some reason presumably related to the launch 
sequence for this mission.

3. The rest of the baseplate is so reflective that a good reflected 
image of the inside of the fairing can be seen in each of the two 
baseplates. It seems to be effectively a mirror. Some other images of a 
spacecraft stack are available elsewhere and show a lot of polished 
metal, this finish carries on across the baseplate.

4. A mirror surface on the baseplate is not a bad idea, indeed I recall 
discussing it some months ago, since it will specularly reflect the 
sunlight away, and if the reflective surface is Earth-facing, as in this 
case in final operations, the reflected beam must miss the Earth. A bold 
move to make a shiny rather than a black spacecraft in order to make a 
dark spacecraft, however.

5. If the antenna panels are blacked (as in Darksat) or shaded (as in 
Visorsat) then there will not be much light reflected to Earth. This may 
be the reason for the recent low estimates of the Darksat brightness 
reported here, if only the back of the solar panel was also visible. The 
higher measurements earlier in the year, just after its launch, may have 
included a part view of the solar panel due to different sun-angles at 
that season. Also, we don't know how precisely the array tracks the Sun 
to know the exact angles it traces.

6. For some reason the fifth, smaller panel was not included in the 
shadow provided by the visor. The reason is not known.

regard

Richard Cole
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Received on Thu Jun 11 2020 - 07:25:51 UTC

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