In article ,
says...
I think folks going to Gateway will do what Blue Origin has done and
opt for LH2/LOX engines, so it will be cryo either way. It will be
large volume 'mild cryo' in LEO (Starship) or deep cryo (LH2/LOX) at
Gateway.

True, but this depends on what lander parts NASA picks. HSF at NASA has
been risk averse since the Challenger disaster. That means they'll
likely pick lander parts that use hypergolic propellants. So Blue
Origin would be out. Starship is never going to be picked as part of
the lunar architecture because it will be seen as "high risk".

Plus NASA mandated a three stage lander. That screams hypergolics from
the start. Neither Blue Origin's Blue Moon lander nor Starship would
qualify in NASA HSF's mind.

The big 'delay' in exploration beyond the Moon is that I
think the NASA plan assume in situ fuel manufacturing on the Moon
before they go for deep space. Deep Space exploration vehicles would
fly to Gateway, refuel with lunar LH2 and LOX, and depart. This makes
some sense in that getting fuel up from the Moon is much 'cheaper'
energetically than boosting it up from Earth, but it impacts your Mars
infrastructure as well, since now your in situ fuel factory there has
to find ice and make LH2/LOX out of water rather than making LOX and
liquid methane out of the atmosphere.

I've heard the water to LH2/LOX argument before. I find it lacking.
Again, we're talking NASA here. The agency who signed off on solid
aluminum wheels for all of its Mars rovers. The wear and tear on those
is mind boggling. They're literally falling apart after what I would
consider to be a pathetic number of miles/km traveled.

And we expect NASA to mine water, on the moon (with its abrasive dust
environment), and turn it into LH2/LOX? I'll believe that when pigs
fly.

All the engineering competitions (mostly college level) I see to mine
lunar regolith have everyone starting from scratch. Because we all know
that no one on earth moves around dirt/rock or mines anything, right?

There are industries on earth that know how to do this and they aren't
run by aerospace engineers. Adapting earth equipment to do this on the
moon would be the most straightforward way to go. The problem with that
is this equipment is *heavy*. But there are reasons it's heavy!

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.

I'm not arguing that we shouldn't invest in lunar water mining. I'm
just against putting it on the critical path to send people to Mars.
It's simply not needed if something like Starship/Super Booster works
out. It's quite simply a hell of a lot easier to refuel a
Starship/Super Booster on earth using methane/LOX (both super cheap on
earth) than it is to mine water on the moon.

Jeff
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