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This spray seemed to be there throughout the entirety of the Stage 2 burn but was especially visible once Stage 2 cutoff had happened.

As that nozzle uses radiant cooling, it can't be cooling fluid, so what could it be?

enter image description here

Video here.

marked-down
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Rory Alsop
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  • I think it is the gas generator exhaust and is being used to vent residual fuel. But I cannot find confirmation of that yet. (Also noticed it). This was a very light payload so probably lots of fuel left in second stage to vent before reentering. – geoffc Feb 23 '18 at 13:29
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    I've asked a couple of related questions about this thruster/exhaust/whatever it is before - I'm unaware of an answer on this site yet that categorically states precisely what it is with sources. – James Thorpe Feb 23 '18 at 13:54
  • I don't think it can be a thruster, as it was there all through the entire 2nd stage burn. – Rory Alsop Feb 23 '18 at 13:54
  • @geoffc They shouldn't be venting much before all satellites get deployed imho. And they might need some fuel for the deorbit burn. So probably not venting all residual fuel. But def looks like some purge at least. – jkavalik Feb 23 '18 at 16:33
  • I was thinking it was venting excess fuel left in some of the pipes and turbo pumps after shutdown – Jake Blocker Feb 24 '18 at 15:40
  • It was there all the way through 2nd stage burn, not just after shutdown. – Rory Alsop Feb 24 '18 at 15:40
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    I don't think that's the gas generator exhaust: the GG points down, not radially, and the exhaust sits higher. – Hobbes Mar 21 '18 at 12:46
  • May I suggest you modify the question in the light of the comments so far? It seems no one has the justified belief that it represents normal operation nor feels confident enough to describe how it could plausibly be a minor fault. How about "If this is a fault, what is the failure mechanism?" – Puffin Mar 22 '18 at 09:54
  • @puffin - no. That is not the question I am asking. – Rory Alsop Mar 22 '18 at 12:03
  • @Hobbes gas generator exhaust is routed into the bell to provide film cooling. I agree with the comments and answer this is a LOX vent, probably part of keeping the pipes chilled down (prevent gas bubbles during engine startup due to warm pipes). – Saiboogu May 23 '18 at 14:21

1 Answers1

6

The thing circled in the photo is a LOX vent. The puffy white snow-like stuff is solid oxygen. It was described at T+1.05:25 in the Iridium-6/GRACE-FO webcast.

Bob Jacobsen
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