Specific impulse
Specific impulse I was many times using the term specific impulse. So, let's speak about it in more detail. Specific impulse (usually abbreviated I sp ) is a measure of how efficiently a reaction mass engine, such as a rocket using propellant or a jet engine using fuel, generates thrust. A propulsion system which has a higher specific impulse uses the mass of the propellant more efficiently than a propulsion system with lower specific impulse. Now, in the case of a rocket, this means less propellant is needed for a given delta-v, so that the vehicle attached to the engine can more efficiently gain altitude and velocity. For all vehicles specific impulse (impulse per unit weight-on-Earth of propellant) in seconds can be defined by the following equation: Thrust is force, the thrust obtained from the engine (newtons or pounds force), g 0 is the standard gravity, which is nominally the gravity at Earth's surface (m/s2), I sp is the specific impulse measured (seconds), dm/dt