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Information in this answer and in this answer shows that Derek C. Breit's hand-held video of the Falcon Heavy 2nd stage near the end of its six hour Earth orbit was recorded in the last minutes before the 2nd second stage burn which put it in heliocentric orbit.

It is bright, fuzzy, and hour-glass shaped. Why?

If this is related to thrusters, why are they visible in the sunlight, and what maneuvering are they being used for exactly?

Here is a tweet with a snippet of the video. The whole thing can be downloaded (see the linked answers for the details).

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    $\begingroup$ I'd say its boil-off from the 2nd stage. Its not cryogenic and thus venting is to be expected. Its looks rather similar to other images of venting upper stages. But this is just an educated guess, I don#t have enough hard data for an answer. $\endgroup$ – Polygnome Nov 5 '18 at 16:04
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    $\begingroup$ Well, the S-IVB was also white and it boiled off a fair amount, so yes. $\endgroup$ – Polygnome Nov 5 '18 at 16:10
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    $\begingroup$ Well, what I meant is that those stages can not maintain minimal temperature and simply allow the fuel to warm up and boil-off / vent. A cryogenic upper stage would make use of re-liquification to reduce boil-off to a minimum. NASA had already doen reasearch about full and partial and full re-liquification in the 60s. $\endgroup$ – Polygnome Nov 5 '18 at 16:30
  • $\begingroup$ I thought more along this line: books.google.de/… $\endgroup$ – Polygnome Nov 5 '18 at 16:38
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    $\begingroup$ I just found this interesting article about "Zero boiloff tanks" (ZBOT) by NASA: nasa.gov/mission_pages/station/research/experiments/1270.html $\endgroup$ – Polygnome Nov 5 '18 at 19:00
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The Falcon Heavy 2nd stage is fueled by cryogenic fluids, but is not sufficiently isolated against warming up. Excess pressure from boiling fluids has to be vented in order to maintain safe pressure levels inside the tank(s). This actively limits the lifetime of the upper stage.

As an educated guess, this is what the image shows. It is consistent with other images of venting spacecraft, especially the Falcon 9 itself. The hourglass shape likely comes from venting with two vents, one on each side.

Here is another image of Falcon 9 venting fuel:

https://i.stack.imgur.com/xkQZJ.jpg

The hourglass shape is consistent with what we see here, but in the latter image (from Zuma) the roll of the rocket seems more pronounced.

Another image (also of the zuma mission) can be found here:

https://twitter.com/Samcornwell/status/950499540666331136

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