Re: yesterday's Starship test (SN8).
In the last few seconds of the flight, the camera switched to the engine bay, and there seemed to be a lot of pale green flame.
Now, Wikipedia says the Raptor engines have spark ignition, but the green flame suggests TEB.
Anyone know?
Emergency/auxiliary ignition system?
Hi,
There have been some ideas from the more respected YouTubers about this.
The main theme is that when the ship was horizontal and the fuel is not at the bottom of the tanks, the pumps aren't primed.
There is a solution fitted that, from what I gathered, has a holding priming tanks of fuel/oxydizer that they spurt in as the craft becomes upright and gets it pumps up to speed and flowing.
The consensus is that there may not have been enough to prime ALL the pumps and one rocket ran "RICH" which can produce a green flame.
Voice of Thunder and Scott Manley have very good presentations.
Tom.. 
There is at least one rocket scientist on here to my knowledge, but it's up to him if he wants to reveal himself.
From what I saw on SpaceX's website and Teslarati there is copper in the engine bay and the green plume of smoke was from the copper being burned.
I've often wondered how they manage ullage on the free-falling boosters.
I'm going to have to find some better technical references.
TheMemberFormerlyKnownAsAWOL:
I've often wondered how they manage ullage on the free-falling boosters.
I guess part of the answer is that they are not free falling as they experience wind resistance, so there is some acceleration to push the fuel to the bottom.
I wondered about the last-minute flip manoeuvre, and if it was maybe a little too late.
Hi,
Check Everyday Astronaut, he has been doing some very indepth docos on spacex rockets.
There is some video around somewhere on YouTube from a camera in one of the Spacex fuel tanks showing fuel movement.
This is inside a Saturn 1 (SA-5) tank, with some commentary.
Tom..
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