While I was creating some spreadsheet formulas for Juno I've come to realization that ISP of kerolox, methalox and hydrolox doesnt matter.

I was creating a formula to optimize 2 / 3 stage rocket formula from this video.
https://www.youtube.com/watch?v=eiGhqsNSMm0

What I found is, structure for hydrolox is much heavier and in the end all 3 of the fuels mentioned above act same.

Here is an example to replicate it. Take a staged engine and set it to %25 size. (163 kN thrust)
Other constants are 1t payload and 11t wet mass (1.51 design TWR)
and adjust fuel tank size to hit total 11t mass.
11t 1.51 TWR ASL
hydrolox 7,63 fuel / 4.34 dv / 2.9m burn time
methalox 8.47t fuel / 4.27 dv / 2.5m burn time
kerolox 8.65t fuel / 4.31 dv / 2.5m burn time

other than burn time and cost all fuel is basically same. TBH structure weight of fuel tanks are unbalanced ATM.

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    per 1000 liters its about 550 liters fuel and its about 18.57 kg of structure per area of fuel tank. Now its time to figure out of threshold of diameters to include in rocket design parameters.

    1.8 years ago
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    After some tinkering I found out, fuel tank mass is related to its area and not its volume. pretty much on low volume tanks doesn't benefit from low density fuel.

    1.8 years ago
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    what you have found is merely a single data point, graphing over a range of wet fuel amounts should show the effect more clearly

    1.8 years ago
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    The fuels are designed to be equivalent, the difference is use case, methalox for TWR, Kerolox for density and cheap, Hydrolox for high efficiency long burn.

    1.8 years ago

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