# Need check for propellant volume & mass calculations

#### N_Molson

Donator
Hello, :tiphat:

As I'm developping a rocket stage, I'm currently focusing to find realistic values that correlate the stage volume and the mass of the propellants.

So here are the raw data :

Fuel : H2 (liquid)
Oxydizer : O2 (liquid)

Stage dimensions : 4 x 30 meters (cylinder)

(it's a little more than that, but I kept several meters for intertank, tank shapes & engine).

Stage volume : 376.991 m3 (cubic meters) = 376,991 liters

And here are my results :

... based on data I found about the Space Shuttle ET, and using Wolfram Alpha :

LOX tank : 150 kPa ; 90.4°K

LH2 tank : 230 kPa ; 20.4°K

Using an oxidizer/fuel ratio of 6:1 I have :

62,831.833 liters of O2, or 71,642 kg

314,159.167 liters of H2, or 22,302 kg

Total mass of the propellants (LOX/LH2) : 93,944 kilograms.

But when I look at the Shuttle ET data, I feel that the proportions aren't the same... Where am I wrong ? :idk:

#### Sky IsNoLimit

##### New member
The oxidizer/fuel ratio means how many kg of oxidizer are burnt with how many kg of fuel. This a mass ratio, not of volumetric ratio!

For your example every 6kg of liquid oxygen are burnt with 1kg of liquid hydroden (O/F ratio = 6:1).

Liquid oxygen has a density of about 1140kg/m3 and liquid hydrogen of about 71kg/m3.

So 7kg of propellant (6kg of liquid oxygen and 1kg of liquid hydrogen) need a volume of 6kg/(1140kg/m3) + 1kg/(71kg/m3) = 0.01935m3.

So total propellant density is 7kg/0.01935m3 = 361.8kg/m3

Finally your rocket stage with a tank volume of 376.991m3 contains 376.991m3 * 361.8kg/m3 = 136395kg (about 136.4t) of LOX/LH propellant.

I hope this helps