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Hello,
I'm unsure of what the terms of Isp or impulse mean in relation to the measurement of engine power. Could someone please explain these terms to me in a clear manner. It would help in understanding the differences in engine systems. Thank you.
Cordially,
EarthWolf
" Man will not always stay on the Earth. "
Konstantin Tsiolkovsky
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Specific impulse has nothing to do with how powerful a rocket engine is, it is a measure of how much push (total) you get per pound of rocket fuel. So, you could have an engine with very high impulse (Isp) but very low thrust like ion engines. Chemical rockets have very high thrust, but with their low Isp they need a great deal of chemical fuel.
So, an ion engine and a chemical engine can both push a rocket ship to the same speed (nothing to slow them down in space), but an ion engine can do it with much less fuel. A chemical engine can do it very quickly, but uses loads of fuel... But there is a point of diminishing return, where the ion engine for instance takes such a long time to accelerate, that it can't get going very fast before it reaches its destination or the cargo needs to get to its destination quickly (like people). A chemical engine speeds up the rocket rapidly and the fuel expended quickly, so it can go faster from the start...
So which one is "faster" depends on your situation
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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impulse= change in momentum= change in velocity*mass
Isp= specific impulse= impulse/mass
Basically, the isp of an engine is equal to the velocity of the exhaust of the engine. However, it is usually measured in a weird way. Instead of measuring it in meters/second, it is usually measures in (lb(force)/lb(mass))*seconds, or just in seconds. What this means is that if an engine has an isp of 100s, it will be able to produce 1 lb of force for 100 seconds using 1 lb of fuel. If you multiply the isp value by g(9.8 m/s^2), you get the velocity of the exhaust in m/s.
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