We don't 'do' fuel questions, but what about this one? Should it be closed or is it 'innocent' enough? I lean towards accepting it.
This question is about how a highly space-related technology works. We answer such questions all the time.
We close questions about how to home-make stuff, most importantly fuel. The question does not ask how you would make a combustion chamber at home. It asks how one works in principle.
I do not see any reason why that question should be closed.