[huhnmonster]

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?

[orost]

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.

[tw04]

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...

[mulmen]

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

[tw04]

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.

[mulmen]

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.

[fabian2k]

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.

[luizfzs]

"engine-rich combustion" has become my favorite expression

[aazaa]

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.

[Diederich]

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.

[rajup]

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

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

[NikolaeVarius]

Which it does not use

[handol]

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