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What is that white smoke coming out of the SN8? It comes out at the bottom and it starts when the first engine stops, why is that?

enter image description here

I think I have seen it coming out from the top too:

enter image description here

This is also visible on SN10 right from the moment of launch, before any engine shutdown. Screenshot from the official video: enter image description here

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    $\begingroup$ Yes it looks very good thanx $\endgroup$ – Joe Jobs Dec 15 '20 at 16:10
  • $\begingroup$ I had thought that it might be nitrogen from the manouvering jets. It did fly some way out to sea, after all, and they would certainly be helpful starting and stopping the belly flop. $\endgroup$ – simon at rcl Dec 17 '20 at 15:38
  • $\begingroup$ Yet the smoke comes out right after the first engine shutdown, way before belly flop $\endgroup$ – Joe Jobs Dec 17 '20 at 16:51
  • $\begingroup$ There are multiple sources of white smoke. $\endgroup$ – simon at rcl Dec 17 '20 at 16:54
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What you are pointing at is almost certainly the CH4 tank venting.

When I read the title, I thought you meant more about the venting that looks like it was coming from the bottom, as seen around 3-4 minutes, especially after the first engine shut down.

From the SpaceX video feed, some screen caps:

Three minutes in, one engine

4 min in, still one engine

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  • $\begingroup$ Yes I am asking about both. What is this smoke coming from the bottom? And how can it have low pressure when the fuel is boiling and has to be vented? You vent it for having too much pressure otherwise you dont vent it $\endgroup$ – Joe Jobs Dec 14 '20 at 21:24
  • $\begingroup$ @JoeJobs: the pressure at the moment whatever-it-is passes through the vent may be pretty high. Immediately after that it's free to expand into the air and the pressure will rapidly fall. If the amount that is venting is small you'll end up with a plume as you see at the top of the vehicle. I don't know if the plumes from the bottom associated with shut-down engines are the same thing. $\endgroup$ – tfb Dec 15 '20 at 16:52
  • $\begingroup$ CH4 venting so close to engine fire and not taking fire itself?!? $\endgroup$ – jumpjack Dec 16 '20 at 9:15
  • $\begingroup$ FYI to trigger a notification: the question has been edited to include SN10 which might be more informative (closer-in picture on where it's coming from). $\endgroup$ – WBT Mar 9 at 1:28

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