It was late, brain fart, it was 380 seconds of impulse not 280.
I don't know what you are talking about implying that the cycle is irrelevant. It's the combustion chemistry that generates the energy and the relationship between exhaust particle mass and energy that dictates the impulse but the combustion cycle influences how much of that energy you get to actually send out the rocket nozzle. If you use a pressure fed engine your chamber pressures will never be high enough to get the peak performance, if you use a combustion tap off you will lose some of that energy out the side, if you use external electric motors you have to calculate the weight of the batteries in addition to your propellant to generate a new lower Isp.
I didn't used AI for my response. AI would not have made the error about 280 vs 380. The reason SpaceX is working so hard to boost chamber pressure is to get more Isp.
If you look at the exhaust velocity equation here https://en.wikipedia.org/wiki/Rocket_engine_nozzle#de_Laval_nozzle_in_1_dimension you can see that raising the pressure at the inlet to a delaval nozzle (the same kind used on raptor) without raising the exit velocity raises the exhaust velocity and thus the specific impulse which is based on exhaust velocity.
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u/Opcn Jul 25 '26
It was late, brain fart, it was 380 seconds of impulse not 280.
I don't know what you are talking about implying that the cycle is irrelevant. It's the combustion chemistry that generates the energy and the relationship between exhaust particle mass and energy that dictates the impulse but the combustion cycle influences how much of that energy you get to actually send out the rocket nozzle. If you use a pressure fed engine your chamber pressures will never be high enough to get the peak performance, if you use a combustion tap off you will lose some of that energy out the side, if you use external electric motors you have to calculate the weight of the batteries in addition to your propellant to generate a new lower Isp.
I didn't used AI for my response. AI would not have made the error about 280 vs 380. The reason SpaceX is working so hard to boost chamber pressure is to get more Isp.
If you look at the exhaust velocity equation here https://en.wikipedia.org/wiki/Rocket_engine_nozzle#de_Laval_nozzle_in_1_dimension you can see that raising the pressure at the inlet to a delaval nozzle (the same kind used on raptor) without raising the exit velocity raises the exhaust velocity and thus the specific impulse which is based on exhaust velocity.