How many engines can be of depends heavily on when the go off. Even 10s of flight can make a huge difference. Generally Merlin engines on the Falcon 9 are incr

How many engines can be of depends heavily on when the go off. Even 10s of flight can make a huge difference. Generally Merlin engines on the Falcon 9 are incredibly reliable. In over 200 flights there were only a couple of engine failures. Some worked nominally on accent but had some failure during landing. > How many do they anticipate regularly? The vast majority flights should never have an engine out. This is something that should generally never happen. I think SpaceX would hope that far less then 1% of flights have an engine out issue. Anything else I don't think they would consider acceptable. SpaceX will redesign the Raptor engine as often as they have to to get the reliability to Merlin levels.