Lo, on the 11/8/2020, Greg (Strider) Moore did proclaim ...
"Snidely" wrote in message news:mn.3d6c7e4b28a58571.127094@snitoo...

With a quizzical look, JF Mezei observed:

What is so different with Falcon9 that allows it to ingnite its own
engines that nobody else can do?

Designed for restarts from the beginning. Most second stage engines are
also so designed, plus the shuttle main engines. I don't know if SLS has
retained that capability, but Wikipedia suggests that the RS-25 has it
still ... dual-redundant spark igniters in the injectors of the preburners.

The SSME were not designed to have relight capability. I don't know the
details, but a pad abort for example required them to do servicing.
Since there was no real reason for inflight reignition ability, my
understanding is they never put it in.

Ooops. Or OMS.

/dps

--
"This is all very fine, but let us not be carried away be excitement,
but ask calmly, how does this person feel about in in his cooler
moments next day, with six or seven thousand feet of snow and stuff on
top of him?"
_Roughing It_, Mark Twain.