Transit time is lower, but the currency of space travel is delta-V, and by that measure, Mars is just as close or closer.
I would guess that the Moon still slightly wins as far as transport costs, but the advantage is much smaller than you'd think, and the far greater resources available on Mars (as well as effective immunity to solar particle events and micrometeorites that Mars' atmosphere provides) tilts the situation strongly in favor of Mars for actual settlement. Joy trips may be cheaper to the Moon, however.
Assuming your tug is in the translunar orbit (going in a figure 8 around the Moon and Earth with the intersection being the Earth-Moon L1 point. And assuming the tug is significantly more massive than your cargo. As you cross the L1 point you can use a mass driver on the tug to 'shoot' the cargo out behind you which would decelerate it to a low delta-v relative to the elevator base (and slightly boost the tug on its way) and when you came around the other side you hook the cargo through a loop like the old mail planes did [1] and pulling it away (which would impart a small deceleration on the tug as it headed back to earth). Depending on masses and how closely you could match things, the amount of delta-v you would need for the tug to keep its orbit true should be very manageable.
[1] https://postalmuseum.si.edu/collections/object-spotlight/sky...
You might save 2km/s if you can use an elevator on the moon. Which is not a lot compared to a space elevator on Earth, but it would definitely be useful. That could be half your delta-v budget if you're going between the moon's surface and an orbit around Earth/Mars/Venus.
Wouldn't you get the same benefit from a Mass Driver, since the moon is a vacuum body?
This makes me question whether you actually understand how orbital rendezvous works. How about as an exercise, you explain why I would say this. Otherwise, I think the resulting conversation would be tiresome and not worth my time.
The relative speed of a capsule and the mass driver will be very high IF you're using the mass driver to slow down substantially. That's in the definition, you're using it to slow down so the initial relative speed at contact must be high. The higher the speed the less energy you have to waste lowering your orbit (slowing down beforehand). If you're slowing down beforehand enough that your relative speed of contact is low then you don't need the mass driver to brake.
If you can't explain my analogy, then I'm just going to conclude you're trolling based on my previously stated disdain for DK syndrome.
> There are two points in space where an elevator's docking port could maintain a stable, lunar-synchronous position: the Earth-Moon Lagrange points L1 and L2. L1 is 56,000 km away from the Earth-facing side of the Moon, (at the lunar equator) and L2 is 67,000 km from the center of the Moon's far side, in the exact opposite direction <snip />
> Both of these positions are substantially farther up than the 36,000 km from Earth to geostationary orbit. Furthermore, the weight of the limb of the cable system extending down to the Moon would have to be balanced by the cable extending further up, and the Moon's slow rotation means the upper limb would have to be much longer than for an Earth-based system, or be topped by a much more massive counterweight. To suspend a kilogram of cable or payload just above the surface of the Moon would require 1,000 kg of counterweight, 26,000 km beyond L1.
So, we're talking an ~80,000 km one?
> the engineering requirements for constructing a lunar elevator system can be met using currently available materials and technology.
Just because something is theoretically possible doesn't mean it's feasible or practical to build in real life. For example, we have known that it's theoretically possible to build vacuume sealed trains, aka the hyperloop, since before the first airplane took flight. And yet whilst you see planes fly everywhere, you don't see any vacuum sealed trains.
Just because something ticks the checkbox of being theoretically possible doesn't mean it's practical or feasible to build.
Maybe in a few hundred years we'll have the means to build something on that scale. It still takes $10k to put 1kg in LEO, imagine the cost of transferring to the Lagrange points.
We have already gone to the Moon. Given that the travel time is relatively short, radiation is far less of a concern.
This is why the Moon is attractive. We know how to get there already and it's not too difficult, all things considered. The problem of how to get there and back with humans aboard has already been solved. It's never been done to Mars.
http://onlinelibrary.wiley.com/doi/10.1029/2009GL041721/abst...
It's only 360km across though...
That seems okay for probes and maybe problematic for people.
Although the poor slob plan comes to mind:
https://books.google.com/books?id=7ejGJaFjLccC&lpg=PA154&ots...
[1] https://youtu.be/Jv5LjA62Uw8?t=3480 [2] https://youtu.be/Jv5LjA62Uw8?t=3644
They're both definitely too far for a rescue mission or evacuation that wasn't planned for in advance. In terms of the old eggs/basket metaphor, it becomes a question of whether you want to use half your straw to weave a second basket, just in case the first one breaks, or if you want to use all of the straw to make your one basket as strong, redundant, and well designed as possible.
From LEO to the surface of the moon is 5.9 km/s
From LEO to the surface of Mars is 4.1 km/s
Source: https://en.wikipedia.org/wiki/Delta-v_budget#Delta-vs_betwee...
If we treat that as equivalent to settling on Mars, then for them to settle on "the moon" would have been a mere 26 miles from London. Perhaps Canvey Island on the River Thames. If we can't manage settlements that close, we really aren't ready yet for the long voyage across the sea.
In terms of delta-v, the budget for the moon is upwards of 50% that for Mars.
EDIT: The 50% figure is from memory, and upon further reflection is probably not quite right, so take it with a grain of salt. I just wanted to point out that distance is not the only relevant metric.
You're actually underestimating. Mars has an atmosphere, so spacecraft can use aerobraking to significantly reduce the delta-v required to get there. The moon has no such benefit — propulsion is required all the way to the surface.
The advantage of the moon, of course, is that it's not limited to transfer windows every two years. If there's an emergency or resupply is needed (or you just want to expand the mission), another lander can be sent at any time. (With some restrictions, like hitting your desired landing spot and making sure the sun wasn't in the Apollo crews' eyes at landing. But regardless, no longer than 28 days between windows.)
Look at the size of the Apollo.
Back on-topic, the discovery of water on the moon makes this more achievable there; otherwise Mars's resources might have actually meant less resources were required.
[1] https://www.youtube.com/watch?v=h2nqgKL2JQU [2] https://news.ycombinator.com/item?id=15093353
Look at the marvel that is the Skycrane. Not needed for the Moon.
No. It's thin enough you can't land with parachutes alone. It's still enough that Mars Global Surveyor used it to make up a 1,250 m/s delta-v deficit.
Is landing on Mars more complex than a thick atmospheric landing on parachutes or an exoatmospheric landing on propulsion only? Yes. But the atmosphere still saves you a lot of delta-v.
It took MGS 15 months (not counting delays) of aerobraking to do that. MGS only weighed 1000kg too. Maybe it could work for shipping large, pre-assembled, empty hab modules to Mars before people get there. (Low density, higher drag, no rush.) But not practical for actual human bodies or even resupply since the Hohmann transfer takes a mere 8.5 months. Adding an aerobraking maneuver could easily triple the transit time.
Surface probes do direct descent trajectories. There is no extended series of repeated braking passes. You do it in one go.
Also, you can use lithobraking.
[1] https://www.jpl.nasa.gov/video/details.php?id=1090; or on Youtube: https://www.youtube.com/watch?v=h2I8AoB1xgU
https://space.stackexchange.com/questions/2046/delta-v-chart...
Note that you could use Spectra/Kevlar or other common high strength materials with a taper ratio of only 4:1 with a lunar elevator. It might take "only" ~50 tons of spectra to hang the weight and allow lifts of a 1000kg or so... its much more doable than earth or mars.
Maybe at the end of the day, the dumb, brute cost of traversing an extreme distance is a tougher problem than colonizing someplace nearby thats vastly less habitable. One problem is conceptually simpler but extremely costly, the other is conceivably lest costly overall despite being way more complicated.
Most of all the moon would be an excellent way station for asteroid mining .
https://www.space.com/22287-elysium-space-station-science-na...
Like most technology, it flows from the rich to the poor eventually as it becomes cheaper. The important part you omitted is that it leaves the rest in a worse relative state. Their absolute state is no worse, and likely better.
Arguing against a backup for civilization (or more appropriately, a backup for the species) because it will be used by the rich is like arguing against a cure for cancer because the rich will benefit before anyone else. In the end, a cure existing still drastically increases the chance the poor might be able to make use of it, from zero to some non-zero amount.
This is all also ignoring the fact that when it comes to species level propagation and survival, I would rather Hitler and his closest Nazi associates makes it off world sustainably in the event of a species level disaster than nobody. My commitment to making sure Humanity survives is much more than my commitment to ensuring we are a caring and accepting civilization. We can rediscover valuing life, but once we're gone, the chances we are coming back are essentially nil.
At a meta level, if you truly don't care about the survival of your species (even if only through the survival of your own relatives and loved ones), you're an evolutionary dead end.
That said, I also don't really think I see being an evolutionary dead end as too huge of a concern. Many of us appreciate things that aren't truly keen from an evolutionary perspective. Consider how many of us will remain happily childless (perhaps not yourself) well into our 30s and beyond. Not amazing for propagating our own personal genes and yet, they're decisions we actively and happily make.
The idea is that if it's between all people dead, or all people except evil space Nazis, I'll take evil space Nazis. Just because they are evil space Nazis now doesn't mean they will be hundreds of years from now, but they'll never get that chance if all humans are gone.
Human history is largely a story about bigoted, insular racist violent psychopaths becoming slightly less of each of those things over time. I don't see why that trend won't continue in general even if we hit a local maxima of fascist oppression from time to time (as this would be).
Because I love people, I can understand the concept of loving people in general, and want other people to be able to experience that. Human extinction means that nobody might ever experience that again, and I think that's a shame, and will do what I can to prevent that type of outcome.
> Many of us appreciate things that aren't truly keen from an evolutionary perspective.
There isn't appreciation of that type without people to do the appreciating. Your ability to appreciate it is provided by our current circumstances. I think keeping those circumstances active is worthwhile. Otherwise you are taking more than you are giving to the species as a whole, which is unsustainable if too many people do so. Even if you don't care about how sustainable it is, you would be riding on the hard work the rest of the species is putting into the system to propagate. Don't be taker.
And that's exactly why it's important.
> Survival of humanity isn't important universally.
Unless there is something there that cares about it, there is little reason for the universe to exist - nothing would know the difference.
Which is why it actually is important universally.
> But it's the most important thing for humans.
No, it's more important for the universe to have humans, than it is for humans to have a universe.
If the universe did not have humans (or another sentients) then it might as well not exist. AKA: Humans super important to the universe.
If humans did not have a universe, then humans would not exist. If humans did not exist then nothing is important to them.
1. What if humans become extinct in a few hundred years? Should the universe then not exist anymore and make more lifeforms?
2. What if there are billions of other "intelligent" species in the universe? Why should the universe care about one specific species that is actually not that great, and very destructive.
3. What if this universe is just an experiment, a petridish and we are just one out of billions of parameters.
4. What if our kind of intelligence is really not that impressive, what if intelligence of dark matter entities, which we don't know about anything is much more powerful, what if even that is not that impressive?
Again, the universe doesn't care. It is not a person, it doesn't have a plan, it is neutral, unless we met our "gods" one day. Humans are just a blip among much larger things that are happening in the universe.
I didn't say that. I said there is no difference between a universe not existing, and one that has no one who notices that it exists.
Re: 1 and 2 I said "(or another sentients)".
3: I guess you are implying someone made the universe and is running it? In that case, they are the ones aware of it, so that counts.
4: Hu?? What are dark matter entities? We notice the universe and care that it exists. That's enough. The specific level of intelligence, (or aggression for that matter) does not matter.
> Again, the universe doesn't care.
That's the point. WE care, and we are the ones that give the universe a "voice" as you will. We speak for it, we do the "caring" for it. Without us (or other sentients) it might as well not not exist.
> Humans are just a blip among much larger things that are happening in the universe.
Just because someone is big doesn't make it important. Importance comes from meaning. A really big explosion in space, that does noting at all, is completely unimportant. While a tiny little seed that someone wanted to plant matters a lot.
So at lest partially universe care about humanity.
Solar fusion creates heavier elements. Gas clouds collapse into stars and planets.
Life, while insignificant on a mass scale, nonetheless represents one of the greatest increases in complexity and diversity the universe has thus far produced.
For that reason alone, it's sacred, and should be cherished.
It is therefore essential to creating self-sustaining spores filled with Earth-life.
Humanity must survive if Earth-life is to survive.
As such, humanity also gets to pick the species (or subspecies) that get included in the spores. Autotrophic algae will likely get a guaranteed berth on the ship, whereas elephants are going to have to breed themselves down smaller and smarter if they want off this rock.
Backing up the species is about keeping a strong diverse stock of human genetics and knowledge somewhere safe from whatever harm might befall the earth.
Under those terms, I for one do not care whether it's rich people or poor people. I doubt I'll be in the 0.00001% of the population who are part of it regardless.
Dry implies flat and drab to me. If anything, I think Stephenson's flaw as a writer is that he comes across as an excited boy who just wants to tell you everything he's been researching, rather than show you naturally with a well-written story.
Can't do that for Mars.
(And don't forget to take an ebook-reader with you in the spaceship with an extensive e-books library).
One of the most significant points in the Moon's favor is the (relative) ease with which a space elevator could be built. It doesn't need unobtainium, current structural materials are strong enough.
Anyone who plays KSP can confirm this for you, especially using the Real Solar System mod, though the same lessson is apparent even in the stock game.
Is that 2.1km/s really a whole extra stage? Or can it be met by reducing cargo capacity somewhat?
Two interesting points about Red Dragon - it wasn't feasible to put parachutes on it so its aerobraking would have been greatly limited. It wouldn't have much surface to use for deceleration in that case. I'm curious just how long it would have spent aerobraking, SpaceX's docs don't seem to mention that. And it was cancelled a few months ago with the intent of designing a "vastly" heavier lander, for which aerobraking will be that much less practical.
edit: But I can do a back of the envelope calculation. Decelerating 6500kg from 6km/s to 540m/s is 116G joules. The diameter is 3.6 meters so a molecule of air in from of the Dragon would be displaced (on average) 0.53 meters. Let's assume the atmosphere is a constant density (0.020 kg/m^3). Assume a drag coefficient of 0.05 (and ignoring the lifting body effect) that is around 200kN of force, tapering down to 1.5kN. That is like 3000 km of aerobraking at maximum atmospheric density and should take around 2300 seconds. But that depends a lot on the deorbit profile. I'm going to need a bigger simulation...
It's not an ideal design, but this way they would only have had to make minor changes to the capsule, mainly to add more fuel for the landing than the regular design.
I believe the extra delta-V you need to get to Mars is less than the delta-V you need to slow down to land on the Moon.
And for almost everything that is not launching related (radiation, resources, ...) a Moon colony faces the same difficulties with better recovery possibilities in case of catastophic failure, so it's a better learning ground (I mean, if your food producing bio dome or whatever dies for some reason you probably want to be on the Moon with emergency supply very close rather than out there on Mars).
The only downside I see is that a Moon colony would not offer the same quality of "backup for civilization" as Mars would, and it's also a harder sell on the public and politician I think.
Once you get there, almost everything is a little easier on Mars, but getting there (and back?) is a heck of a lot harder.
Is this because we havent found them yet, an educated guess or the moon somehow gets rid of these?
CO (and then CO2) form at high temps, so elemental carbon doesn't have much chance to condensate to a "rock" form in regards to non-stellar celestial bodies. These float off into space, no atmosphere to contain them.
At the temperatures/pressure of the moon, Nitrogen rapidly boils off and floats away as well.
Not sure about Phosphorus and Sulfur, but I'm sure they can be either directly or indirectly related back to the moon's lack of an atmosphere as well.
I just think if we are talking about an extraterrestrial base for the sake of "backing up" the human race then it is prudent to pick a location that isn't in any way dependant on the master copy.
However I appreciate other concerns also take priority as well (cost, practicality, etc) but if the topic were strictly just about backing up humanity then my ideal candidates would be Mars plus some location outside of our solar system. But I'm venturing well into the realm of sci-fi now.
If there's no humans, the possibility to restore is gone.
At that point, asteroid mining may be cheaper than launching resources from earth.
https://api.media.ccc.de/v/31c3_-_6180_-_en_-_saal_2_-_20141... Around 19'th minute.
Then again, Mars is far so it would take some time to get there. Then again again, most of the ships wouldn't have to have people aboard. Edit: It helps that Mars has an atmosphere of sorts.
A moon base is much simpler in both scenarios and return trips are achievable (has already been done FORTY YEARS AGO).
When he says the real science is on Mars, though, I'd raise the challenge and say it's on Europa, Enceladus, Io, Ganymede and Callisto. I mean hot oceans protected from radiation through tick ice. What else do you need?
We may find fossil and even bacterial life on Mars (and that would possibly be the greatest human discovery yet), but I bet we can find a thriving ecosystem full of complex multicelular life on one of those Moons.
Also, as others have pointed, closer/further is a tricky thing when talking about interplanetary travel: http://www.marssociety.org/home/about/faq/#Q12
There's at least one colonization plan floating around using what's essentially Apollo-era hardware for getting to Mars for that Delta-v related reason.
TLDR: The moon colony will be able to make its own rules and keep earth at bay.
You make the government local, or the local government that eventually forms will rebel. Then it will beat you, because it can react to the local situation more quickly.
You might be able to control the Moon from Earth, but Mars will definitely be self-governing. It's all about the latency.
The comparison you should be making is the rebellion of a distant colony versus a more local rebellion. I.e. why did the American Revolution succeed, but the Whiskey Rebellion fail?
The Whisky rebellion was essentially an armed tax protest, of the kind that happened fairly often in American history and before independence. Its goal was never to topple the US government or create a separate nation.
I like how the power roles between the sexes on the moon are reversed too. The matriarch has all the power because women are scarce and they take on many husbands out of this need. They always hold the cards and culturally everyone accepts this.
Also, because the value of women is so high no man ever dares attack one less they be sent out an airlock. It is cultural justice. No trial. A man just knows that if he is seen assaulting a woman, he is dead. The community can't afford to lose a single female.
Plus with all the talk of the A.I. Armageddon the book plays right into that discussion.
The book is interesting, but it was written for a society that doesn't exist. Women and men will not be as lopsided in a colony. The first few ships might be mostly male construction workers, but after that expect to see a much closer balance.
I do hope the future will be more "centrist", neither patriarchal nor matriarchal.
The main difference is that Mars has sufficient weather that the dust is roundish, whereas the moon dust is composed of extremely sharp shards.
IMHO, if we can't make a go of it on the moon, we have no business going to Mars.
But seriously, since you're going to be unnecessarily pedantic, you're still wrong. Bones (even dry ones on earth) have a MUCH higher percentage of water content than the average location on Mars or the Moon.
Perhaps you could explain why nit-picking is so important? HN isn't a science forum. There's no expectation that people post full scientific justification (with references) for what they say.
It should be about people making polite conversation. Instead, you're missing the point entirely. Which is sad.
Would digging a big valley (no dome), and putting air in it be ridiculously inefficient? Of course you'd lose some over time, but at what rate?
A lot of the things (majority) that would eradicate life on earth would also eradicate life on the moon.
I'm guessing the long 28 day(day) cycle is the biggest issue, along with few natural resources.
Moreover, only half of the Moon sees the light of the Sun. This fact alone reduces available surface for settlements to only half of the Moon.
While the Moon could be a temporary backup plan, in the long-term, you're going to need to terraform a planet and make a suitable atmosphere, both of which are not possible to do to the Moon.
Edit: Thanks to the commentators below who mentioned that while the Moon is tidally locked to the Earth, most of its surface does indeed receive light from the Sun.
Only one question though: If that is true, then why do they call it "the dark side of the Moon"? (Honest question)
This doesn't refer to sunlight, it refers to radio communications. The back of the Moon, relative to Earth cannot receive any kind of signal we can send without some kind of artificial relay. Because the moon it tidally locked with the Earth the same side always faces us.
So the back side is always dark to our radio even though it has about a 28 earth long "day". Any (non-polar) spot on the Moon gets about 14 Earth days of light and then another 14 of darkness, corresponding with the phases of the moon we see here.
I'm no astronomer but the moon is tidally locked to the earth and not the sun, which means that the moon should have sunrises/sunsets...
This mathematical effect is incredibly important, it means that sunlight, during the day, averages out to being half as strong as its maximum over the whole of the Earth's surface. The calculation isn't even particularly difficult: the surface area of a sphere is well-known to be 4πr², half of that or 2πr² is illuminated at any one time, but the actual irradiation that we receive is proportional to the cross-section area, which is just the area of the circle: πr². So if the Sun-directly-overhead light were to be illuminating that entire half of the world, we would get k·2πr² light for some k, but instead we only get k·πr² light for that same k, so it works out to be 1/2 when averaged over the whole surface of the Earth.
While I was at university a fellow student asked me to guess the coldest place in the Solar System. I guessed "the middle of the dark side of Mercury." I guessed this for a couple reasons: (1) I knew I needed a rock without an atmosphere since atmospheres sustain convection currents that transmit energy, and (2) I figured since Mercury is so close to the Sun it's probably tidally locked to the Sun and therefore this part probably has not seen a speck of sunlight in millions of years.
It turns out that general relativity makes point #2 wrong and my friend gleefully informed me that he was looking at an article (there were many, so let's take [1] as representative) suggesting that it might be in a crater on the South pole of the Moon. This has basically the same reasoning of (1) and (2) above, except substituting the shadow of a crater for the shadow of tidal locking. But Mercury is still in the running -- the only issue is that we might not be looking at the dark side of it, but rather, again, at its poles.
[1] https://www.space.com/7311-moon-craters-coldest-place-solar-...
I think you are drastically overstating the difficulty of heating a lunar polar base. You are surrounded by vacuum, one of the best insulators around. It can be used.
Of course a lunar base would probably be underground (for more radiation protection) and the lunar soil would quickly wick heat away. Simple to deal with. Excavate a small cavern and suspend the base inside the cavern. Aluminize the cavern walls if possible. Now the colony has its own thermos bottle and staying warm is easy.
Sunlight is just as intense at the lunar poles as the equator. The ground receives less solar energy, but that doesn't mean that less energy is present. In fact there is more solar energy available at some sites since the panels could receive light continuously instead of in 28 day cycles. (Might require putting the panels up on a tower to help reduce libration shadows?)
Vacuum is only one of the best insulators around if you're near other warm things, I'm afraid. Out in space the dominant form of heat exchange is the Stefan-Boltzmann law, which says that if you have a half-acre of total surface area on your moon-base, and it's at 300 kelvin, then you need to supply about a megawatt to keep it warm.
It's not an insurmountable problem, of course -- Tesla just announced a battery for Australia at 129 MW-hrs, which would sustain the thing for 5 days, which is not enough but it's only a half-order of magnitude off. (I'm also not considering something like nuclear heating; it's not uncommon to have a 1000-megawatt nuclear reactor in the US and that's just the power output, not the heat -- so it's not a terribly bad way to go if you can shield the rest of the base from it. The only hazard with that is one recently discussed by John Oliver on his show, firing nuclear things into space is heavily, heavily complicated by the nowhere-near-close-enough-to-zero failure rate of launch rockets and the insanely-scary-cost of distributing a bunch of reactor-grade nuclear fuel into the atmosphere.)
Historical aside: before we had good solar panels, people tried crazy stuff like the Phaeton satellite that used a generator spun by a heat engine powered by liquid mercury heated by parabolic reflectors. Let's bring that idea back.
1MW only requires a 30 meter by 30 meter thermal solar collector. Pump that 1MW of heat into the hab and run a heat engine, using the shell of the hab as the thermal sink. Now that constant 1MW drain is a required feature.
In fact our best understanding of why Mercury has the 3:2 relationship appears to be (if I'm reading these papers right) "because of historical reasons." That is, now that it's in that state, that state is stable and unlikely to decay to the 2:1 or 1:1 state, but getting into that state is much less clear and potentially requires that in the past, the other planets of the Solar system had nudged Mercury into a more eccentric orbit than it has now. The claim is that the eccentricity of that orbit caused the 3:2 resonance, then in more recent history these perturbations from other planets averaged out more to make Mercury's orbit less eccentric, but it still holds on to the resonance from its past.
It's the side we can't see from Earth. It's dark as in unreachable by line of sight or light, eg radio communication, from Earth. "Far side of the moon" is the preferred term but "dark side" is popular and persists.
What do you mean by this? The moon is tidally locked to the Earth, but the entire surface sees sunlight over the course of ~a month with the exception of a handful of polar craters where small portions are perpetually in shadow.
That's not true. There is a side of the Moon that's always facing away from us on Earth but each side of the Moon actually gets about 2 weeks of sunlight followed by 2 weeks of darkness.
Or to put it in human terms, like holding a shield of 1.25 cm of radius with your arm of 75 cm.
It will not protect you really very much.
There's hope for light most of the year at the poles: https://en.wikipedia.org/wiki/Peak_of_eternal_light
I used to fantasize about exploiting the temperature gradient between hemispheres for generating electricity on worlds with long days like Mercury and the Moon when I was a kid.
Because four billion wordwide population - all living - have a Computer God Containment Policy Brain Bank Brain, a real brain, in the Brain Bank Cities on the far side of the moon we never see.
Many of the same benefits Musk seeks (backup for Civilization, excitement) for a fraction of the cost.
Low gravity and atmosphere on a dome would be more complicated, but again, compared to Mars, it's right there.
It would be a more humble and realistic first step, IMO.