Specific impulse

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 with a higher specific impulse uses the mass of the propellant more efficiently. In the case of a rocket, this means less propellant needed for a given delta-v,^[1]^[2] so that the vehicle attached to the engine can more efficiently gain altitude and velocity.

^ "What is specific impulse?". Qualitative Reasoning Group. Retrieved 22 December 2009.
^ Hutchinson, Lee (14 April 2013). "New F-1B rocket engine upgrades Apollo-era design with 1.8M lbs of thrust". Ars Technica. Retrieved 15 April 2013. The measure of a rocket's fuel effectiveness is called its specific impulse (abbreviated as 'ISP'—or more properly Isp).... 'Mass specific impulse ... describes the thrust-producing effectiveness of a chemical reaction and it is most easily thought of as the amount of thrust force produced by each pound (mass) of fuel and oxidizer propellant burned in a unit of time. It is kind of like a measure of miles per gallon (mpg) for rockets.'

[QRG1-1] "What is specific impulse?". Qualitative Reasoning Group. Retrieved 22 December 2009.

[ars20130414-2] Hutchinson, Lee (14 April 2013). "New F-1B rocket engine upgrades Apollo-era design with 1.8M lbs of thrust". Ars Technica. Retrieved 15 April 2013. The measure of a rocket's fuel effectiveness is called its specific impulse (abbreviated as 'ISP'—or more properly Isp).... 'Mass specific impulse ... describes the thrust-producing effectiveness of a chemical reaction and it is most easily thought of as the amount of thrust force produced by each pound (mass) of fuel and oxidizer propellant burned in a unit of time. It is kind of like a measure of miles per gallon (mpg) for rockets.'

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