I'm kind of blown away that the engines don't have to be torn-down and rebuilt or something after being ignited and shut down like this. I assumed that since t

I'm kind of blown away that the engines don't have to be torn-down and rebuilt or something after being ignited and shut down like this. I assumed that since the booster stages are not re-usable, the design would be more optimized for "one use". And the controlled explosion of a rocket igniting seems to count as "one use". Clearly I'm wrong. I guess they are so robust (for saftey & redundancy reasons) that a few seconds of burn don't do any irreversible damage.