Well, I hope it isn't the final topic!
I actually prefer the middle option, extending operations far from Armstrong Base to other regions of the Moon. I think the pole is the right region to explore in detail if we have to be stuck with just one, but there would be a lot of desire to check out other regions in more detail than even Artemis managed; who knows what we might discover there?
The problem with a reusable lander--assuming that the idea is to provide it with just enough propellant to go one way, being refueled at the end to go the other--is one that horrified me with the generally engaging Selene Project timeline by sts-200. In that TL the Anglo-French Selene team have decided to go with "LSR," Lunar Surface Refueling, for their 1970s moon landing project. This means the manned lander will reach the surface of the Moon without enough fuel for the ascent stage to return them to Earth, but they will refuel from another unmanned vehicle that has landed previously, with enough propellant to send them on home.
What is terrifying about that is that once the descent to the Lunar surface has gotten well under way, there is no survivable abort option for them; either they successfully land near their refuel depot, close enough to bring the propellant over and pump it in, or one way or another they are dead. Unless they can survive on the Lunar surface long enough for Selene to launch another depot vehicle to land safely near enough for them to go get their fuel then, anyway. Since everyone in the TL except possibly the Russians have given LOR unreasonably short shrift, everyone is paying a higher price than they have to for the manned missions and so the effective payloads to the Lunar surface are eaten up by heavier than necessary manned facilities and higher than necessary fuel loads, so that makes it even harder.
But the general principle remains even with more efficient LOR or Lagrange basing of the Earth return vehicle--if we take advantage of the efficiency of one-way landing or takeoff missions, we sacrifice the ability to abort a landing back to orbit. I suggested in the other TL that this might be OK with a Moonbase in place--but even here where we have one I have cold feet about it.
At some point one must take off the training wheels I suppose, and take such risks. In your TL there is ample experience and engineering advances to justify it I suppose.
I am also nervous about using up Lunar ice by using the hydrogen in it as propellant. A less wasteful course would be to replenish just the oxygen, which is 6/7 or more of the mass of hydrogen-oxygen propellant mixes, using Lunar hydrogen reusably to extract plentiful oxygen from regolith, but retaining the hydrogen for use on the Moon, including this catalytic function of course.
So my wimpy, overcautious response to option 1 is to suggest continuing to use Earth derived hydrogen for both legs of descent and ascent (which means oversized tanks for the ascent, less than half full) but to refill the oxygen tanks with Lunar derived LOX for ascent. And since such a vehicle still would not have landing-abort capability (plenty of light hydrogen, but not nearly enough oxygen) that it be used only for bringing cargo down to the Moon and perhaps for shipping Lunar mass back up. The latter can include human beings, but I'd want humans to come down on different descenders riding in abort-to-orbit modules. This means we'd either be not using the ascent capability of the cargo vehicles for human operations, or we'd be accumulating lots of spare emergency ascent vehicles that sit unused for years and decades and eventually become unreliable.
I suppose a standard descent module could be developed that can take down either cargo or an extra-heavy abort-capable human crew module, retaining enough hydrogen to carry its dry mass with a modest oxygen refuel back to orbit or L-2. Then if it were desired it carry a cargo up, the small reserve of hydrogen would be supplemented by Lunar LH and LOX for a payload to be brought up as well.
If we continue, for safety's sake, to bring all humans down in modules fully fueled for a return to space, but switch over to sending them back there on more efficient hydrogen-oxygen fueled reused standard stages, we'd start to accumulate lots of hypergolic fuels I suppose.
But these can possibly be put to good use, perhaps as fuel or anyway abort-return propellant for the reusable long-range exploration modules._------
As for the Mars options--well, Mars is a long way away. With the sorts of engines developed in the TL, we are looking at options no better than envisioned in the 1960s. We'd have to use slow minimum-delta-V orbits, exposing the crew to both GCRs and solar wind radiation for a very long time. Then upon reaching the vicinity of Mars, land something there. If we are going to improve on 1960s visions by developing in situ refueling, we need to ship considerable physical plant down to the Martian surface as well. Then, can we use ISR to do more than merely enable the landers to return to Martian orbit, and even go so far as to send up tanks of fuel for the mission to return to Earth--or must not the Earth return phase still rely on propellants supplied at launch?
Winchell Chung just happened to mention on his Atomic Rockets site that Deimos might have a lot of volatiles, including one hopes water--anyway any volatiles that contain hydrogen can be used, along with oxygen obtainable from many materials, as well as water, as a source for hydrogen-oxygen engine fuels. In this TL, it is asserted, rather plausibly one fears, that Phobos is pretty dry--but if Deimos is moister, then I'd suggest that the first destination of a manned Mars expedition would be that moon. Land the whole big ship on it--with the tiny moon's gravity it would be more like docking with it--and start digging out radiation-proof habitable voids in the regolith immediately, to be filled with inflatable habitat for the crew to move into. Then go prospecting for water or other useful volatiles; if it turns out there is plenty to be had (based on Lunar polar mining experience) start extracting it for the return. Then and only then move on with landers to Mars, relying on in-situ refueling of them to return back to Deimos.
Practically speaking it would be necessary to know in advance of any manned mission whether Deimos is a suitable ISR site or not; that would be done either by robot probes or by a manned mission with an assured return fuel supply just in case; the latter approach would be more justified if they were going to start assembling the anti-radiation habitat regardless of whether they find water or not. Or, robots might be able to get cracking on starting to accumulate an ice reserve that suitable tankage and plant might be sent on later to convert to fuel.
Come to think of it, blocks of ice might actually be superior to raw regolith as radiation shielding.
So--a Mars project strikes me as a worthy one, but it is a big big deal, involving a lot more than Apollo did. It is much more like von Braun's 1950s notion of lunar exploration with a massive lander in the hundreds of tons with a crew of 50 or so--first we need to establish a Deimos base, then a Mars base, before it is possible for a single person to land and be returned--oh, it is possible to do it as a stunt without all this investment, but the price of a low-value "quick" single astronaut landing and return would be not a lot less than the massive investment of doing it right.
Meanwhile--technology might advance to offer us better options. I like the nuclear fusion pulse idea those wacky dudes at the University of Washington are working on for instance, that is supposed to come on line by the 2020s or so. I see no reason why parallel developments would not be occurring in the ATL. So with a high ISP, relatively high thrust option developing that might allow missions to reach Mars and return within a three month window (or alternatively allow slower missions to deliver a much larger fraction of launched mass) there would be some wisdom in holding off on going to Mars until these nifty technologies are well in hand.
If in the interim, Lunar exploration and exploitation are being developed apace, the infrastructure for leveraging Lunar resources into multiplying the capability of Mars and asteroidal expeditions would also be there. Such infrastructure might even enable missions to operate in Venus's upper atmosphere, and perhaps control landing vehicles designed to operate at the high ambient temperatures (if we could only develop a power plant for them that would work sustainably--even a nuclear fission core probably won't be hot enough to get power out of efficiently at those high environmental temperatures. Oh well--maybe it would be OK to get power inefficiently, if there is enough of it...)
So I am willing to once again put Mars on the back burner, if it means that instead we move to Luna to stay, and start developing a serious industrial colony there.
