John Bucknell was Senior Propulsion Engineer for the Raptor full-flow staged combustion methalox rocket at SpaceX and is currently the Senior Propulsion Scientist for Divergent3D in Torrance, CA developing additively manufactured vehicle technologies.
Specific impulse (usually abbreviated Isp) is a measure of the efficiency of rocket and jet engines. By definition, it is the total impulse (or change in momentum) delivered per unit of propellant consumed and is dimensionally equivalent to the generated thrust divided by the propellant mass or weight flow rate. You can think of it like miles per gallon for cars. Higher ISP is better.
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