Specific impulse

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Propellant Typical Isp (seconds)
Zinc + Sulfur 240
Aluminum + Ammonium Perchlorate 287
Hydrazine + Nitrogen Tetroxide 313
Ethanol + Oxygen 330
Methane + Oxygen 370
Hydrogen + Oxygen 465 (space shuttle)
Hydrogen + Fluorine 545 (HF acid exhaust)
Hydrogen + Ozone 580 (liquid ozone unstable)
Beryllium + Oxygen 710 (toxic exhaust)
Hydrogen + Thermal Energy 800-1000
Ion Electric 3000 (low thrust)
Nuclear Pulse 5000 ?
Fluid-core Nuclear 10000 ?
He-3 Fusion 2 million ?
Antimatter 30 million ?


Specific impulse is a measure of the effectiveness of a fuel in a type of engine, usually for either rockets or jet engines.

It can be measured by running the motor and measuring how much fuel it burns and how much total thrust it has produced. If you divide the total amount of thrust by the amount of fuel consumed then you can find the specific impulse.

For a fuel, the specific impulse can be calculated by calculating how many seconds a quantity of fuel could generate enough thrust to support the weight of that mass of fuel. For example, 1kg of fuel might be able to generate enough thrust to carry the weight of 1kg of fuel (9.81Newtons) for 450 seconds. The specific impulse of that fuel would then be 450.

The same calculation can be done for all sorts of engines, but it is mostly used for jet and rocket engines because it makes it easier to compare the effectiveness of different systems.

It is possible for one fuel (eg hydrogen) to be used in more than 1 type of engine and each different use of the same fuel would generate a different figure for specific impuse.

External Links

From Wikipedia