In article ,
says...
At any rate, once you reduce launch costs to put a reasonable amount of
equipment on the moon to start production of LH2/LOX in quantity, you
need to compare the new, lower, cost of launching LH2/LOX (or better
yet, methane/LOX) from earth to that mined on the moon. If you take
into account all the money it's going to take to maintain that
(expensive) infrastructure on the moon to produce that propellant, I'm
not convinced that it's going to break even in terms of the economics in
the next 25 years or so.


So Mars is right out, then, since in situ fuel production is so hard
and it's REQUIRED if you're going to do Mars?

The difference is in the effort that the in-situ propellant production
requires. On Mars, you've got some filters and vacuum pumps to pull in
CO2 from the thin atmosphere and your gas processing equipment that can
be located inside the landing craft (protected from the elements).

On the moon, we don't really know what we'll need to produce water in
quantity. Some people think it will be as easy as scooping up some
loose surface material from the lunar south pole area and baking it so
that the volatiles (mostly water) come out. I think that's going to be
a lot harder than it seems since we have zero actual surface data on the
properties of said surface material that is "high" in water content.
Add in the abrasive nature of the lunar regolith and you have a recipe
for constant breakdowns of equipment exposed to that regolith.

IMHO, lunar in-situ LH2/LOX production will be at least an order of
magnitude harder (which means more expensive) than in-situ methane/LOX
production on Mars done with LH2 brought from earth. Bringing the LH2
from earth makes the initial process much easier for those first Mars
missions. Later missions can likely get their H2O from Mars as well,
but it's not strictly necessary, so this provides for one more stepping
stone on the path.

Jeff
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