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# Total Impulse

Impulse is defined as a force acting on an object over time, which in the absence of opposing forces (gravity and aerodynamic drag), changes the momentum (integral of mass and velocity) of the object. As such, it is the best performance class (payload mass and terminal velocity capability) indicator of a rocket, rather than takeoff thrust, mass, or "power". The total impulse of a rocket (stage) burning its propellant is:[2]:27

{\displaystyle I=\int Fdt}I=\int Fdt

When there is fixed thrust, this is simply:

{\displaystyle I=Ft\;}I=Ft\;

The total impulse of a multi-stage rocket is the sum of the impulses of the individual stages.