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Early in the video of the launch of the first sixty SpaceX Starlink satellites we can see that after stage separation the first stage grid fins open.

Around that time there are some phenomena I don't recognize after about 16:44:

  1. bright flash of light
  2. blue "plasma clouds" (I don't know what it is really)
  3. bright white glow of the grid fins, fading to dark.

This was a launch in darkness and I don't think that sunlight was at play here. It seems to be a color camera of some kind (the blue stuff) so the grid fin glow isn't thermal IR, it seems to be white light.

What's going on? What causes these three phenomena?

(sorry for the low quality GIF, I used ImageJ because Giphy won't accept long YouTube videos.

SpaceX Starlink Mission screenshots

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  • $\begingroup$ Giphy won't accept long videos, so I stitched screenshots into the GIF using ImageJ. If anybody knows an easy way to make a better looking GIF for SE, possibly with Python, please let me know! $\endgroup$
    – uhoh
    May 25, 2019 at 12:42
  • $\begingroup$ The light source is the 2nd stage ignition (happening behind the camera). $\endgroup$
    – amI
    May 26, 2019 at 6:53
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    $\begingroup$ at 16:46 (T+00:02:46) you get green TEA/TEB glow in the 2nd stage engine on right, and this green light illuminates the 1st stage on the left. From there on, brightness and color on the right has corresponding changes on the left, until the 2nd stage is far away (or the grid fins are in shadow). $\endgroup$
    – amI
    May 26, 2019 at 8:51
  • $\begingroup$ @amI okay I'll take a look as soon as I get to a reasonable device, thanks! $\endgroup$
    – uhoh
    May 26, 2019 at 8:56
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    $\begingroup$ I was hoping someone could say whether the bright streaks are ice and the cloudy blobs are cold gas and what are their sources. $\endgroup$
    – amI
    May 30, 2019 at 9:30

1 Answer 1

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That's just the illumination and plasma from the adjacent 4.95 Gigawatt plasma blowtorch impacting the first stage at 3 km per second.

I.e. It's the second stage Merlin 1D Vacuum engine igniting, and spewing its exhaust all over the first stage.

Wherever it hits a flat surface, or a surface sufficiently convoluted to entrap some of the plasma in the exhaust, the plasma stagnates and glows.
Also of course if it hits the stationary exhaust of a RCS thrust, although there it's more just the intense light shining on the N2 puffs.

It fades quite quickly, as the second stage is exiting the immediate scene at a bit less than 1g of acceleration, while the first stage is swinging around to show its own backside towards the light.

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  • $\begingroup$ Is it actually ionized plasma, or just luminescence from excited atoms and molecules undergoing chemical reactions? $\endgroup$
    – uhoh
    Aug 10, 2021 at 15:36
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    $\begingroup$ @uhoh it was inside a Merlin 1D combustion chamber about 1/20th of a second previously, so while it has cooled from expansion, it would not yet be in thermal or electrostatic equilibrium. . But most of what we see is not glowing, it is just a VERY bright light shining through diffuse gasses. $\endgroup$ Aug 10, 2021 at 16:07

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