/sci/ - Science & Math

>>12444296
Methalox torches blowing hot gasses into the various chambers of Raptor, which themselves are lit by electric sparkers.

>>12443989
You're correct on all counts.

>ignition
Raptor ignites using torch-augmented spark ignition. Basically, a spark plug wouldn't be enough to light the preburners or combustion chamber on its own, because the mass flow rates are too high. Instead, the spark plugs are inside of small combustion chambers that have a tiny mass flow rate of propellants, which the spark can actually ignite. Once these little chambers are lit they are venting their hot gas exhaust as a jet directly into the preburners/combustion chamber, which is enough heat to ignite them and get a self sustaining reaction. Picture pic related, but lit by a spark plug rather than a flint and steel sparker, and blowing directly into the engine (also at lower temperatures to not require a cooling system).
>legs
Probably set to deploy once altitude and speed both reach a certain minimum threshold, because you don't want them deploying while still way up in the air and you also don't want them deploying while falling too fast, because in either case the acceleration and air drag may be enough to cause problems with the latching mechanism.
>lost an engine
The only engine the vehicle lost was the engine it tried to land on, unfortunately. As Elon said, low header pressure meant the engine got propellant starved while running at close to full throttle, which likely means cavitation and vapor flowing through coolant lines, meaning insufficient cooling and burnup of pars of the engine (hence the green light coinciding with significant noticeable loss in thrust).