Fuel Volume Efficiency

[Hurricane]

So I had a little argument with someone about what sort of propellant would be most efficient, volume-wise, in order to get the same spacecraft to LEO.
I voted for RP-1, while he voted for LOX/LH2.
I can see his point, LH2 has a much higher Isp, but then again, RP-1 is much, much denser...
I don't claim to know that much about propellants (in fact, I know nothing about them :lol, but that's just what my logic tells me.
Regards, Oz. :tiphat:

 

[Urwumpe]

So I had a little argument with someone about what sort of propellant would be most efficient, volume-wise, in order to get the same spacecraft to LEO.
I voted for RP-1, while he voted for LOX/LH2.
I can see his point, LH2 has a much higher Isp, but then again, RP-1 is much, much denser...
I don't claim to know that much about propellants (in fact, I know nothing about them :lol, but that's just what my logic tells me.
Regards, Oz. :tiphat:

Kerosene + LOX has the higher energy density per volume. You have about 30% higher mass for a first stage of the same trajectory, but it has almost half the volume of a comparable H2+O2 stage.

 

[Hurricane]

Kerosene + LOX has the higher energy density per volume. You have about 30% higher mass for a first stage of the same trajectory, but it has almost half the volume of a comparable H2+O2 stage.

So to see if I got this straight, I can use half the volume of RP-1 + LOX to send up a 30% heavier spacecraft into the same trajectory?

 

[Urwumpe]

So to see if I got this straight, I can use half the volume of RP-1 + LOX to send up a 30% heavier spacecraft into the same trajectory?

No, you need a 30% heavier stage for launching the same payload (or following stages and payload) on the same trajectory (=same pitch profile, same acceleration, same cut-off velocity, and as result: same cut-off time).

While this is rather theoretical to have such similarities in trajectory, it helps in the example to compare the performance.

 

[Hurricane]

No, you need a 30% heavier stage for launching the same payload (or following stages and payload) on the same trajectory (=same pitch profile, same acceleration, same cut-off velocity, and as result: same cut-off time).

While this is rather theoretical to have such similarities in trajectory, it helps in the example to compare the performance.

Oh, I see now.
Many thanks! :tiphat: