Alternatives for Translunar Cycling Spaceships
Adding the return-trip hydrogen in the mass landed on the moon plus the
tanks to hold the hydrogen causes the mass calculation to diverge, so
there's no solution without an additional step in the transportation
We have several ways to fix this:
- One-way tankers carrying hydrogen from Terra to Luna instead of just
from Terra to LEO
- Extraterrestrial hydrogen available on the moon (from asteroids?)
- Mass driver for the boost off Luna
- Mass driver delivering tanks of O2 to LEO
- Aerobraking to LEO (Probably won't pay off because of the additional
weight of the aerobrake plus additional structure)
- On-orbit ferry from lunar surface to lunar orbit (saves more than half
- Nuclear propulsion
- Hybrid boosters, such as aluminum-LOX, made entirely from lunar material
Any of these might work. All of them cost money. Darn.
Using Isp=444.4 sec and a 5:1 mixture ratio
(which matches the RL-10 rocket engine), we get:
LEO to Luna Luna to LEO
Delta V 19,754 19,885 ft/sec
Mo/Mf 3.986 4.023
So, for chemical propulsion between LEO and the surface of Luna, we can use
Mo/Mf = 4 for most conceptual design activities.
The overall mass ratio is improved if we assume the higher performance of
engines such as the Space Shuttle Main Engines, but using a mass ratio of
4 gives us a more conservative analysis.
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