Hi, this may or may not be the right place. I'm making my own fuel tanks for use in RSS, just for fun really, but I'm trying to work out the math behind it. So I have it set up in 2 stages, both LH2/LOX fueled, at a 6:1 mixture ratio. I'm assuming 95% of the volume in each stage is available volume for fuel, which is sort of a guess. I'm using 381s ASL, 455s VAC isp.
So each tank is a 6' radius cylinder. Stage 1 is 140' height, stage 2 is 40' height. I figured out volumes etc, and worked all of this out in Excel, I just want a math check to see if I'm doing this right.
ISP @ VAC: 455s
ISP @ SL: 381s
95% volume of each cylinder is available for fuel storage. (referred to in Excel as Efficiency)
Stage 1 height: 140'
Stage 2 height: 40'
Stage radii: 6' (both)
Went from liters to kgs of fuel by multiplying by density of O2 and H2 (1.1417kg/L O2, 0.07078kg/L H2).
Used volume ratio of SS ET to find amount in liters of each fuel per stage. (72.81% volume is H2, 27.19% volume is O2)
The +5000kg, +10000kg, etc relates to payload capacity. Am I on the right track here? To simplify the math some I just used SL ISP for Stage 1, and VAC ISP for Stage 2.
So this would result in a maximum payload of less than 10,000kg, or am I missing something? If yes, how could I modify it to reach a 20,000kg payload to LEO?
*SS kg/L refers to the weight to volume ratio of the space shuttle ET just as a sanity check.