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Comment by huhnmonster | Hacker News Reader

At around 1:54:50, upon full landing thrust, the exhaust flames turn green. I know colored flames from chemistry classes, but I always assumed that was caused by certain salts.

Rocket fuel, to my knowledge, does not contain any of those ingredients. Can someone explain what happened there? Was this planned?

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Copper burns green, and the engine contains a lot of copper, so I think we saw a malfunctioning Raptor burning itself up.

Other answers mention TEB starter fluid but I don't think that's right, because as far as I know Raptor has spark ignition only.

edit: Elon Musk just tweeted that the immediate cause of the crash was low pressure in the fuel tank, so that would make sense, as running oxygen-rich would overheat and melt the engines.

I believe it was burning through the copper liner due to fuel starvation (oxygen rich which makes it SUPER hot)

http://photos1.blogger.com/blogger/1613/496/1600/Merlin1C_Ch...

Seriously getting downvoted? That's what caused the issue.... Elon already tweeted they had low fuel pressure...

You may be right but Starship uses Raptor engines, not Merlins.

I'm aware, the picture was to show what the liner looks like (approximately), the engines are of similar design. I apologize if anyone thought that was literally the liner in question.

Ah yeah, lots of confusion re: TEB in other comments. Seems like a lot of people have the Raptor and Merlin mixed up so at least in this context probably have to be explicit.

I really don't know enough about this, but this might be "engine-rich combustion". Which would also explain why the landing part didn't work.

"engine-rich combustion" has become my favorite expression

Copper and boron, according to Wikipedia, will give green flame:

https://en.wikipedia.org/wiki/Colored_fire

But given the extreme conditions, a number of other factors could be at work.

I think that was caused by the out engine trying to re-start itself using TEA-TEB.

EDIT: Correction: Raptor doesn't use TEA-TEB.

Most likely the chemical used to (re)start the engine, triethylborane (TEB)

https://en.wikipedia.org/wiki/Triethylborane.

I thought the raptor was going to use a spark plug.

Which it does not use

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