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The moon has some additional practical hurdles compared to Mars:

1. No atmosphere means no weathering, so all of the moon dust is incredibly sharp and easily coats equipment when it gets kicked up. This dust quickly wears out joints and contact surfaces.

2. The Moon's low gravity and lack of atmosphere mean that you have to carry extra propellant to land.

3. Lack of easily extractable resources. It is comparatively easier to extract water and CO2 on Mars to generate methane for a return trip. A trip to the moon requires carrying all of the fuel for a return trip as well.

Nuclear-powered ships built in orbit would drop transit times significantly but I wonder if they'd significantly reduce Mars <-> Earth costs (you'd still need Starships to shuttle payloads through the atmosphere). They are probably required for mining the asteroid belt though...

2. The Moon's low gravity and lack of atmosphere mean that you have to carry extra propellant to land.

Lack of atmosphere I get, but how does low gravity require more propellant to land?

(edit: maybe you meant lack of atmosphere due to low gravity, and I got the other meaning contrary to your intent)

You have to use the engines to slow down rather than aerobraking in the atmosphere.

Sorry, my first thought was that it requires more delta-v to enter a lunar capture orbit since the gravity is weak, but I just double checked the delta-v roadmap and it's actually not that high.

However, it is a bit problematic that landing a rocket on the lunar surface can kick rocks around the planet (thanks to the low gravity), possibly into orbit or beyond (which could pelt other equipment). So you need to switch to an entirely different propulsion system for descent, which carries a payload penalty.

https://upload.wikimedia.org/wikipedia/commons/9/93/Solar_sy...

Mars is considered to be the hardest planet to land on in the entire solar system, you have to carry a heatshield or you will burn to a crisp, but it's so thin you still have to land propulsively using rockets. You definitely need to sacrifice less spacecraft mass to land on the moon

Also there is some water on the moon so you can make rocket fuel, though how much exactly remains an open question

Water yes, but I haven't seen anything about CO2 so I think you're stuck with hydrogen-oxygen engines (which have different tradeoffs than methane-oxygen engines).

https://everydayastronaut.com/raptor-engine/ (scroll down to the text immediately above the RP1/Methane/Hydrogen chart)

There is a lot of oxygen on the Moon (combined with silicon and aluminum), but carbon is not readily available, so it'd be more favorable to hydrolox engines.

> Mars is considered to be the hardest planet to land on in the entire solar system

Questionable.

> but it's so thin you still have to land propulsively using rockets

You have to do the same on earth. Starship sized vehicles have to land on earth propulsively too.

Sure, you can do somewhat larger payloads to Orbit without engines but for large things you need to have real engines.

> You definitely need to sacrifice less spacecraft mass to land on the moon

On the moon you can't aerobrake, that is far worse.

> Also there is some water on the moon so you can make rocket fuel, though how much exactly remains an open question

There is a huge difference. Water on the moon has to be mined from permanently shadowed craters. The water is frozen and incredibly hard, its more like mining stone on earth.

On Mars there are places where you can literally land, drill down and make yourself an underground lake pretty easily. Or land basically right on an ice sheet.

On the moon you need to figure out how to get energy down into the crater, you need sophisticated mining equipment, all that equipment needs to handle incredibly low temperatures.

Mars comparatively is not so far away from earth in terms of temperature for your equipment.

In summation, in-situ for rocket fuel/water is far, far easier on Mars.

Did you just make up the entire passage about ice strength? Why do you feel the need to do that?

Ice is 0.5 Mpa stong in the freezer and 2 Mpa at absolute zero.

Thats tensile strenght of chalk and limestone - you can get that with a shovel. Tensile strength of rock is measured in Hundreds of MPA.

The smallest, wimpiest digger you can find can handle it.

Tests have shown then depending on the situation lunar regolith can go up 80MPa. And the more water is contained, the harder it gets. You get low yield from that, around 10%. So you need to mine a pretty large amount and process it.

So you need to create excavator that operate inside a creator that can operate at extrem temperatures.

On Mars you can literally do what we already do at the South Pole, drill a hole and make it warm.

Its multiple orders of magnitude easier.

Mars has a few things in its favor. It has a (mostly) carbon-dioxide atmosphere that can be used as an ingredient to make methane. It has a normal day/night cycle so you can use solar panels without needing to store two weeks worth of energy in order to last through the night. It has higher gravity. In general, it's just a more hospitable place to live even though it's a lot further away.

We could start on Mars by building stuff in the canyons first at the lowest possible elevation to increase the air pressure. Then you can dome sections of the canyon and pump up the atmosphere allowing large "outdoor" area.

Would also provide radiation shielding.

Sounds like a plan. GO GO GO!

Mars air pressure is really low; I don't think building in canyons would have much benefit if you're concerned about reducing the stress of air pressure on the habitat. Building low relative to the surrounding ground though might have benefits related to radiation shielding, though.

The way I usually picture Mars settlements being made is either finding an existing lava tube and creating an airtight seal on the interior, or digging a hole in the ground, erecting a dome (possibly out of blocks made on-site from local materials), and then burying it in dirt. The dome acts as a compressive structure, and you can inflate a habitat on the inside like blowing up a balloon. Either way, people live underground for the benefit of radiation shielding. And either way, the airtight seal of the habitat has something solid for all that air pressure to press against.

I know that it's 1/200th of earth sea level but based on how deep those canyons are you might get 1/20 at the deepest parts. Maybe enough for water to not immediately evaporate.

Reminds me of Out of the Silent Planet by C. S. Lewis, written before anyone had much of a clear idea of what the surface of Mars is really like. There was air and life in the canyons, but everything else was a low-oxygen desert.

Realistically, though, I wouldn't expect pressure to vary that much with elevation. Mars' weaker gravity implies that it would vary less than on Earth. However, according to this [1], the pressure does vary a lot by season. That's interesting.

> Surface pressure: 6.36 mb at mean radius (variable from 4.0 to 8.7 mb depending on season)

Surface water might not be readily available on Mars, but ice is present on the surface at the poles, and probably elsewhere in shadowy craters or underground. (Unfortunately, the places with the best access to ice are not great for solar power.)

[1] https://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.htm...

I'd love to see some pressure readings from Hellas Basin. It's a full five miles below what scientists say is the average elevation.

Hmm, according to wikipedia, the pressure in Hellas can sometimes get up to 12.4 mbar, and it looks like there are some significant glaciers. Interesting. Tunneling into the ice could be a plausible way to build a Mars habitat...

https://en.wikipedia.org/wiki/Hellas_Planitia

I think you're underestimating the value of "you can breathe the air" and "water is easily available via melting snow" when comparing it to Antartica.

I'm suggesting that Mars may be a more hospitable place than the moon, not more hospitable than Antarctica. Antarctica is a much easier place to survive than Mars or the moon, but the long-term benefits of establishing a permanent human presence are less. We also already have a lot of people living in Antarctica; according to wikipedia, there are about 40 year-round bases, and the population varies from about 4,000 in the summer to about 1,000 in the winter.

> You can have a space elevator on the moon today with a titanium cable.

A space elevator makes no sense on the moon. First of all the orbit is unstable and you would need constant station keeping.

Also, it turns out that if there is no atmosphere you don't actually need an elevator, you can just use electrically driven propulsion without an elevator. You just use a rail gun to shoot stuff into orbit.

> when they get in trouble, there is no help.

But there will be at least one professional doctors and likely a highly advanced medical facility.

> Mars settlement is only viable when we have a spaceship factory on the moon, nuclear engines, and we could send the equivant of a large marine research vessel to mars, so 10,000 tons usefull payload, every month.

You would first need to prove that building such infrastructure on the moon itself isn't far to un-practical and more expensive then going directly from earth.

> "A space elevator makes no sense on the moon. First of all the orbit is unstable and you would need constant station keeping."

In a typical space elevator, the counterweight end of a space elevator is not in orbit. The center of mass of a space elevator would be above geostationary orbit, so the counterweight would be moving substantially faster than orbital speed at its altitude. A space elevator is held taut by centrifugal "force".

For the Moon it would work a bit different; the Moon doesn't spin fast enough for a purely centrifugal elevator. Instead the elevator would pass through one of the Lagrange points, in effect being held taut between the gravitational pulls of Earth and the Moon.

The Lagrange points aren't stable orbits either, but technically the space elevator would be going through a Lagrange point, not sitting inside that region in orbit. I am not sure how much station keeping would be required. You might still be right overall here.

The question is what the advantage is. If you are launch bulk materials, a railgun will be cheaper.

And for human launch a SSTO reusable lander should be fine.

Perhaps the niche for a space elevator is bulk passenger transit. An elevator could perhaps ferry more people than a reusable lander, while not turning them into goo as the g-forces of a railgun might.

"But there will be at least one professional doctors and likely a highly advanced medical facility."

Common, think about this for just a minute - how many medical staff and how many tons of equipment are required to staff even a small rural hospital? An MRI scanner alone weighs 20 tons. Where are you going to get fresh blood for transfusions, skin grafts, or a kidney transplant? Many medical supplies are perishable and won;t last the trip.

A mobile hospital looks like USNS comfort - 70,000 tons displacement and over 1,000 staff. If you could take it apart and sent it to mars, you would need 700 starships.

That's why, when US army deploys a forward operating base, or arctic explorers set up shop, they can't afford to bring an 'highly advanced medical facility'. They deal with basic injuries and stabilise the patient, and send him back to a proper medical facility asap. You can do that on the moon, but on Mars it takes 6 month to travel once every 2 years.

If you are one of the first people on mars, and your spaceship is not the size of a nuclear aircraft carrier, any kind of non-trivial medical problem is a death sentence.

"You would first need to prove that building such infrastructure on the moon itself isn't far to un-practical and more expensive then going directly from earth."

Look, you can argue that cities in space are too difficult, but if you want to argue that a Moon city is impractical but a Mars city is easy - then I think the burden of proof is on you.

Going to Mars carries risks, and not all medical emergencies will be able to be dealt with there. Is that, by itself, going to stop people from wanting to go there? Probably not.

We could reasonably expect any humans going to Mars to bring a lot of medical equipment, supplies, and trained personnel with them. If you need an emergency organ transplant, though, you're probably out of luck.

This isn't substantially different than the risks many people face on Earth, including tens of millions of people in the United States who lack medical insurance. Most people wouldn't accept those kinds of risks voluntarily, but if someone really wants to go to Mars they might decide the risks are acceptable.

If a Mars colony becomes well established with a substantial population, then the risks become less, as the colony would have the infrastructure and full-time expert staff one would expect to find in a typical hospital, and a larger population would mean more potential blood and organ donors.

My point was not that the facilities will be better then the best hospital on earth.

My point was that you will have at least 1 room dedicated and filled with the best available medical equipment and smart people that have thought about what is most needed. There will be likely two doctors and multiple people trained as backups.

That is only on the first flight, over time, as infrastructure grows the medical facilities will grow as well.

Point being here it is not exactly a crazy proposition for somebody to go on that mission.

> A mobile hospital looks like USNS comfort - 70,000 tons displacement and over 1,000 staff.

You are looking forward way far. If there is need on Mars for that kind of hospital with 1000 staff, 700 Starships is not actually that crazy anymore. Not to mention there are likely lots of optimizations as they serve different functions.

Economically, I think one huge advantage the Moon has over Mars, is tourism. The Moon is a practical tourism destination because you can spend a few days there and be off-planet for less than 2 weeks. Billionaires can take the time out of their busy schedules for a few days on the lunar surface. Mars is not a practical tourism destination because a minimum round-trip to Mars is closer to 2 years than 2 weeks. Nuclear propulsion may speed up the journey but even then it is still going to take many months.

Once you get regular tourist trips to the lunar surface for the ultra-wealthy, the economies of scale can drive down the cost and grow the market, and you may have the self-sustaining economics for a permanent lunar population to support these visiting tourists – hospitality staff, tour guides, maintenance staff, medical, construction, spacecraft maintenance (vehicles like HLS Starship can't return to Earth for maintenance but that could happen on the surface), etc.

I don't think it has to be either/or, you can do both – establish a crewed research station on the Moon and establish a crewed research station on Mars. But the former has a much shorter path to evolve from a research station (which is dependent on public funding or private philanthropy) into something economically self-sustaining than the later does.

What if the colony were 10x larger than you imagine?

Each Starship is designed to carry 100 tons to mars, IIRC.

What's stopping them from building hundreds of them?

I think the plan is to send a fleet of them with supplies only to mars first, and then bring them back, and do the trip a second time. It's feasible that once the tech is extant and they work and can be produced quickly, that they build hundreds or perhaps a thousand ships.

But that's kind of my point - once you are talking hundreds of spaceships, setting up a manufacturing shop on the moon will pay off, because you can manufacture and 3D print all the metal parts there.

You can also actually make money from producing telecommunication satellites, startlink sats, etc. and launching them from the moon.

I don't think starship propellant can be made on the moon.

I also don't think it is necessarily easier to manufacture space machines there given the constraints, even if the materials are available. If Starship is fully reusable 100T to orbit for just the cost of the propellant, there is a huge benefit to Earth-based manufacturing in the short to medium term.

But the question is why would you make it there.

The materials will be clearly far cheaper sourced from earth. You can probably make high quality steel on the moon but its not easy. You need to do prospecting on the moon, find what materials are where. You need to refine those sources into the right materials in the right amount.

You need to put a huge mining, refining, and manufacturing infrastructure on the moon at huge cost. And this is far beyond our current ability in robotics.

And 3D printing object of that size has not proven to be the best solution, there is a reason SpaceX builds Starship the way they build it.

And what does it save you? Why would you do it?

The traditional answer was, because launching from earth is expensive. But that very premise is what SpaceX Starship tries to overcome.

Once you have a fully reusable Starship System, having to launch a few more times should not be that expensive.

The infrastructure you suggest itself would require a fully working Starship system anyway. So why would we build that infrastructure on earth, then build the whole infrastructure again on the moon just so we can launch from the moon.

Additionally, all the other things that we want to send to Mars are on earth, including the humans, food, medical equipment and so on.

This simply doesn't make sense once you really think threw all the requirements end to end. SpaceX actually did think threw these things.

The only actually reasonable suggestion is that you could have some mining for water on the moon and then use a railgun to shoot it into earth orbit. But even the economics of that are very questionable and setting something like that up would likely require a working Starship system too.

Manufacturing on the moon simply makes no sense unless you actually want to create things on the moon. There are cool suggestions for that, see this company (who just got a NASA contract to study this further):

https://www.youtube.com/watch?v=9-RTBGnzNks

In the words of Dr. Robert Zubrin:

Why Mars? 3 reasons: Mars is where the science is, where the challenge is, and where the future is.

Give his full answer a watch, it's very interesting: https://www.youtube.com/watch?v=1S6k2LBJhac

I am a much bigger fan of Mercury, though it is less popular (http://einstein-schrodinger.com/mercury_colony.html previous discussion https://news.ycombinator.com/item?id=5734333 )

Mercury is indeed interesting from a colonization standpoint, but it's really less interesting than Mars from a science standpoint. Mars could potentially answer fundamental science questions around the origins of life.

That first link was a very interesting read, thanks for sharing!