What is specific impulse?

Specific Impulse

Specific impulse (usually abbreviated Isp) 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 in kilograms), then specific impulse has units of velocity. If it is given in terms of weight (such as in 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.

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Some articles on specific impulse:

Solid-fuel Rocket - Propellant Families - Composite Modified Double Base Propellants
... makes up the oxygen deficit introduced by using nitrocellulose, improving the overall specific impulse ... The aluminum also improves specific impulse as well as combustion stability ... such as NEPE-75 used in Trident II D-5, replace most of the AP with HMX, further increasing specific impulse ...
LE-7A - LE-7A Specifications
... level) 843 kN (190,000 lbf) Rated thrust (vacuum) 1,074 kN (241,000 lbf) Specific impulse (sea level) Specific impulse (vacuum) 429 seconds Long nozzle Rated thrust (sea level) 870 ...
Rocket Engine Nozzle - Specific Impulse
... be defined as and for perfectly expanded nozzles, this reduces to The specific impulse, is the ratio of the amount of thrust produced to the weight ... equivalent (or effective) exhaust gas velocity at nozzle exit, m/s = specific impulse, s = Gravitational acceleration at sea level on Earth = 9.807 ...
Specific Impulse - Examples - Model Rocketry
... Specific impulse is also used to measure performance in model rocket motors ... Following are some of Estes' claimed values for specific impulses for several of their rocket motors Estes Industries is a large, well-known American seller of model rocket components ... The specific impulse for these model rocket motors is much lower than for many other rocket motors because the manufacturer uses black powder ...
High Power Electric Propulsion - Specifications
... The thruster itself is in the 20-50 kW class, with a specific impulse of 6,000-9,000 seconds, and a propellant throughput capability exceeding 100 kg/kW ... HiPEP produced 670 mN of thrust at a power level of 39.3 kW using 7.0 mg/s of fuel giving a specific impulse of 9620 s ... to 24.4 kW, the HiPEP used 5.6 mg/s of fuel giving a specific impulse of 8270 s and 460 mN of thrust ...

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