Page "Specific impulse" Paragraph 0

Specific impulse ( usually abbreviated I < sub > sp </ sub >) is a way to describe the efficiency of rocket and jet engines.

It represents the force with respect to the amount of propellant used per unit time.

If the " amount " of propellant is given in terms of mass ( such as kilograms ), then specific impulse has units of velocity.

If it is given in terms of force ( such as kiloponds ), then specific impulse has units of time.

The conversion constant between the two versions of specific impulse is g. The higher the specific impulse, the lower the propellant flow rate required for a given thrust, and in the case of a rocket the less propellant is needed for a given delta-v per the Tsiolkovsky rocket equation.