- #71
stefan r
Science Advisor
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- 311
mfb said:From LEO you need 4.3 km/s to reach Mars. From the surface of the Moon you need about 3.5 km/s. If you want to mate a rocket from Earth with fuel from the Moon the fuel from the Moon needs 5.7 km/s delta_v just to reach LEO (3.2 of it can be done with aerobraking) and 5.7 km/s more if you want the system back on the Moon for the next trip - for a sum of 8.2 km/s for a Moon<->LEO shuttle.
The rendevous in LEO might work poorly. Earth-moon Lagrange 1 looks a lot better. From EML1 it takes 1.2 km/s to reach mars. The launch from lunar surface to EML1 needs 2.5 km/s. Getting to EML 1 from LEO requires 3.8 km/s. So the astronauts, rocket, and luggage (and methane?) lose 0.7 km/s when they make a detour to EML1.
The worst part would be landing the methane needed to lift oxygen.
mfb said:If we consider lunar space elevators, we can also consider concepts like the StarTram which can potentially launch things to space at basically the electricity costs once it runs. If LEO launches are as cheap as an airplane flight, there is no point in a Moon-based propellant production, you just launch more from Earth.
If we go solar the electricity costs are lower on the moon. No clouds or atmosphere to block sunlight. The StarTram itself would work much better on the moon. The magnetic sled does not need to leave the surface so magnetic breaks can recycle the electricity. There is no need for a heat shield. The cargo does not hit an atmosphere. The ship does not have to fit into a tube. A lunar StarTram would not need to be elevated so there is no active support structure. Refrigerating kilometers of niobium-titanium conductor drains a lot of power. I have not seen a suggestion for magnetic launch Earth direct to Mars would likely be thousands of km.
Anything that makes launch to LEO cheap or easier will also make establishing lunar colonies/depots cheaper or easier.