| 1. | a measure, usually in seconds, of the efficiency with which a rocket engine utilizes its propellants, equal to the number of pounds of thrust produced per pound of propellant burned per second. |
| 2. | the specific impulse that a given combination of propellants would produce in an ideal rocket engine providing complete combustion, no friction losses, and no lateral expansion of the exhaust. |
| specific impulse n. A performance measure for rocket propellants that is equal to units of thrust per unit weight of propellant consumed per unit time. Also called specific thrust. |