> At the end of the day, there are only 3 things that matter for a rocket engine: exhaust velocity, how fast it can burn the fuel, and the mass of the engine.

> At the end of the day, there are only 3 things that matter for a rocket engine: exhaust velocity, how fast it can burn the fuel, and the mass of the engine. While those are primary factors, and a rocket won't go up if they aren't good enough, they aren't the only ones (or else every rocket engine would be hydrolox staged combustion, like the SSMEs). Other key factors are engine cost (SSME does terrible here), fuel type (hydrolox needs way larger diameter boosters, isn't worth it for first stage), combustion stability (allows engines to throttle, key for max-Q and reducing max g as stage empties, especially on upper stage), reusability (important for some systems), controllability (how quickly it can throttle)... While their importance gradually diminishes, there is a list hundreds long of different trade-offs made in engine development. The reason I said I'd like to know more is indeed because that article wasn't informative. I certainly am not writing it off because it can't be plopped in a rocket right now