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Old June 5th 17, 11:43 AM posted to sci.space.policy
Jeff Findley[_6_]
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Default Mining the moon for rocket fuel to get us to Mars

In article ,
lid says...
Yeah, I use a very simple first order approximation for this:
the mass of the fuel you'll get from the Moon has to be greater than
fuel used to get the mass to mine it to the Moon, otherwise it's a net
loss.

Simply put, if you're going to extract say 100 kilotons of fuel from the
Moon, you're going to have to use less than 100 kilotons of fuel getting
your mining and processing equipment there, otherwise it's a waste.


Perhaps you on purpose ignored this factor in your approximation, but
surely the *location* of the fuel must be considered?

If you use 100 kilotons of fuel to send equipment to the Moon, most of
that fuel is used up close to the Earth, and will not reach the Moon. If
that equipment then produces 100 kilotons of fuel on the Moon, that fuel
is on the Moon, which is "half-way to anywhere".

You would surely have to use *much* more than 100 kilotons of fuel to
deliver a payload of 100 kilotons of fuel from the Earth's surface to
the Moon's surface.


So let's revise the original statement a bit. If the goal is to refuel
a depot in lunar orbit, the fuel you mine, refine, and launch to that
depot must exceed the amount of fuel it took to originally land the
mining equipment, lander, and landing fuel when starting from roughly
the same lunar orbit as the depot. Ignore the delta-V to get to lunar
orbit, because it's the same for the 100 kilotons of fuel put in lunar
orbit or the 100 kilotons of lunar lander, fuel, and mining equipment
put in lunar orbit.

Yes, you can split hairs and come up with "direct" landing trajectories
which might be more efficient, but we're trying to come up with a first
order approximation to illustrate how hard it will be to "break even" on
the mining equipment. It's not going to be as easy as it seems. Lunar
soil is terribly abrasive and will wear out "lightweight" aerospace
materials like aluminum very quickly on equipment that is in moving
contact with it.

And, the cost of that lunar landing stage and mining equipment is going
to be higher than the cost of the fuel mass sent in the other scenario.
We're not even comparing costs yet, just mass "cost".

Jeff
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