What's the reasoning behind NOT colonizing the Moon?

[magnemoe]

6 hours ago, Scotius said:

I wouldn't be surprised if Moon became a major source of mineral resources in the future. At least as sort of intermediate stage before full blown asteroid mining. It's closer. It has (still) usable gravity. Due to lack of tectonic activity, whatever elements are present should be relatively shallow. And if we dig in the craters, we can be reasonably sure we'll find goodies asteroids brought with them

Yes, also the craters is asteroid impacts.
Yes the asteroids is cheaper in dV but the moon has shorter travel time and communication delay so if something goes wrong its much easier to fix. 
 

[MKI]

7 hours ago, monophonic said:

Except you can't. Not one that is useful anyway.

You see, the thing about a space elevator is that you want the upper station to be at the geostationary orbit. That way your space ships can come and go docking to and from your elevator as they please. At any other altitude your ships need to furiously burn rockets right to the moment the docking clamps connect just to match the motion of your elevator station. Strong rocket blast is something you definitely do not want happening right next to your precious space elevator.

Problem with the Moon is that it is tidally locked with the Earth. As it rotates so slowly, once around every 28 days and a bit, the theoretical selenosynchronous orbit is actually way outside the Moon's Hill radius. In other words, you won't be orbiting the Moon at that distance, you will be orbiting the Earth or the Sun.

Now you might think it could help you get started on reaching actual orbit. But you won't get any useful amount of velocity from the increased radius due to the very slow rotation, the difference in gravity compared to the surface is minimal, and there isn't any atmosphere to get above of. You could build a much bigger linear accelerator right on the surface and use less resources on it than building a massive tower to put your launch system higher.

Well there is the Lagrange point between the Earth and the Moon. That would be a nice spot to drop off cargo, right? Just a little push and the gravity from Earth should bring the pod down essentially for free? True, but that spot is over 60000 kilometers from the Moon. Even at 1/6th the gravity I don't think our current materials can handle that, even when not considering the tidal forces on a structure that long.

So there isn't really any point in building a space elevator on the Moon. It wouldn't bring you any advantage over just putting your launch pad on the highest spot of the Moon at the Selenean summit. Now Mars, on the other hand... maybe somebody else can check the numbers for that one?

I never thought deeply about the slow rotation of the Moon and its impact on where/how big the elevator would have to be to even be reasonable 

I've heard kevlar can be used to build the "Lunar Space Elevator". However, I'm not sure if they considered the length required to build the elevator in the first place. But then why would they say its possible, if it isn't possible at the length required haha. I'd put it "close enough to reality" that even the 60k Kilometer distance isn't a complete game killer with modern technologies. Pretty crazy though!

Regardless, I find the idea of a surface level accelerator also being attractive as an easy way to get to orbit from the Moon with a lot less unknowns AFAIK. If its better/more reasonable than a Lunar space elevator is a whole other discussion haha. 

 

Obviously both of these proposals aren't realistic with today's financing, let alone building such a thing, but that's the fun of it right? ;D

 

 

[magnemoe]

31 minutes ago, MKI said:

I never thought deeply about the slow rotation of the Moon and its impact on where/how big the elevator would have to be to even be reasonable 

I've heard kevlar can be used to build the "Lunar Space Elevator". However, I'm not sure if they considered the length required to build the elevator in the first place. But then why would they say its possible, if it isn't possible at the length required haha. I'd put it "close enough to reality" that even the 60k Kilometer distance isn't a complete game killer with modern technologies. Pretty crazy though!

Regardless, I find the idea of a surface level accelerator also being attractive as an easy way to get to orbit from the Moon with a lot less unknowns AFAIK. If its better/more reasonable than a Lunar space elevator is a whole other discussion haha. 

 

Obviously both of these proposals aren't realistic with today's financing, let alone building such a thing, but that's the fun of it right? ;D

 

 

However an mass driver / coil gun can be build much easier and cheaper and it can be used from everywhere even the far side or the poles. 
 

[K^2]

36 minutes ago, magnemoe said:

However an mass driver / coil gun can be build much easier and cheaper and it can be used from everywhere even the far side or the poles. 

This is the reason we absolutely should be building infrastructure on the Moon. It's also why there is zero reason to put any permanent habs on the surface. An orbital station can supply standard gravity and you can even organize a miniature magnetosphere around habitable sections to give you as much protection as anything in LEO. This is all far more problematic on the surface. And a rail/coil launcher can also work for capture, which means you have "free" way to go back and forward. Do a work shift on the surface, then come back to the orbital habitat. All the colonies we should be building would be orbiting the Moon, not on the Moon.

[magnemoe]

18 minutes ago, K^2 said:

This is the reason we absolutely should be building infrastructure on the Moon. It's also why there is zero reason to put any permanent habs on the surface. An orbital station can supply standard gravity and you can even organize a miniature magnetosphere around habitable sections to give you as much protection as anything in LEO. This is all far more problematic on the surface. And a rail/coil launcher can also work for capture, which means you have "free" way to go back and forward. Do a work shift on the surface, then come back to the orbital habitat. All the colonies we should be building would be orbiting the Moon, not on the Moon.

"Also work for capture" makes "we catch the superheavy on the grind fins" sound boring. 
Doable, sure our accuracy is good enough, however I would made an separate loop for this, the return probe will be 1/10 the mass or less, you also want an wider loop for inaccuracy and an catcher at the end. Probably some armor in front if case something failed during final approach. 

And yes you keep most of the crew in orbit or back at earth if their work don't require seconds of  interaction. You still need mechanics on the ground to repair stuff. 
You could also just use dirt as armor as you will launch stuff all the time. 

[K^2]

5 minutes ago, magnemoe said:

"Also work for capture" makes "we catch the superheavy on the grind fins" sound boring. 
Doable, sure our accuracy is good enough, however I would made an separate loop for this, the return probe will be 1/10 the mass or less, you also want an wider loop for inaccuracy and an catcher at the end. Probably some armor in front if case something failed during final approach. 

Valid points, and yeah, you wouldn't capture a personnel shuttle with the same rail you use to send processed ores to orbit. But at least this actually feels like an engineering problem. It doesn't require some super-materials that are yet to be invented or impossible fuels. We have everything we need to build something like this.

 

Also, I just took another look at OP, and I should probably add that I'm of even lower opinion of Mars as valid place for human habitation. For purposes of safety, it's not an ounce better, with an added bonus of Martian soil being toxic on top of getting in everywhere just as well as Lunar regolith. The atmosphere is too thin to provide any sort of protection or even significantly help with landings, but thick enough to have dust storms and to make ascent complicated. Same deal with surface gravity. It's high enough that you have to deal with it when building structures and sending cargo up, but too low for normal human health, meaning at best you'll have to spend a lot of time daily on special equipment keeping yourself in shape, and at worst will put a hard limit on how long you can live on the surface. And building centrifuges is even more of a problem on Mars, because, again, there is atmosphere and dust that gets in everywhere with it. Out of all the places in Sol where we can actually build an outpost, Mars might actually be the worst place to do so.

So it's not so much, "Why we are talking about Mars and forgetting about the Moon?" and more about why are we even talking about Mars? Certainly, we should work on getting boots on the ground there, and having a few research station anywhere we can reach is a good idea, but neither is suitable for permanent habitation, and I don't think that will ever change. Every advancement that makes Mars a little more livable will also make all of the alternatives so much better as well.

[Ziggy Kerman]

8 hours ago, kerbiloid said:

They should start finding asteroids, rich with precious metals, and redirect them into the Moon.

Then harvest.

So resurrecting the Asteroid Redirect Mission, just for profit this time round?

[kerbiloid]

4 hours ago, Ziggy Kerman said:

So resurrecting the Asteroid Redirect Mission, just for profit this time round?

If find a golden asteroids - -why not. Otherwise why bring a tiny 10 m rock with several milligrams of something useful?

[magnemoe]

6 hours ago, K^2 said:

Valid points, and yeah, you wouldn't capture a personnel shuttle with the same rail you use to send processed ores to orbit. But at least this actually feels like an engineering problem. It doesn't require some super-materials that are yet to be invented or impossible fuels. We have everything we need to build something like this.

 

Also, I just took another look at OP, and I should probably add that I'm of even lower opinion of Mars as valid place for human habitation. For purposes of safety, it's not an ounce better, with an added bonus of Martian soil being toxic on top of getting in everywhere just as well as Lunar regolith. The atmosphere is too thin to provide any sort of protection or even significantly help with landings, but thick enough to have dust storms and to make ascent complicated. Same deal with surface gravity. It's high enough that you have to deal with it when building structures and sending cargo up, but too low for normal human health, meaning at best you'll have to spend a lot of time daily on special equipment keeping yourself in shape, and at worst will put a hard limit on how long you can live on the surface. And building centrifuges is even more of a problem on Mars, because, again, there is atmosphere and dust that gets in everywhere with it. Out of all the places in Sol where we can actually build an outpost, Mars might actually be the worst place to do so.

So it's not so much, "Why we are talking about Mars and forgetting about the Moon?" and more about why are we even talking about Mars? Certainly, we should work on getting boots on the ground there, and having a few research station anywhere we can reach is a good idea, but neither is suitable for permanent habitation, and I don't think that will ever change. Every advancement that makes Mars a little more livable will also make all of the alternatives so much better as well.

I would not use this system for manned ships anyway just for cargo as as you only need fuel for circulating, deobriting and control you don't need much fuel. 
And its not the same system, for one the orientation will be different and the catcher probably end in something like an net.

And yes mars is a bit less hostile, the problem is distance so its hard to evacuate or get emergency supplies. Moon has the benefit that its useful for resources and an tourist destination. 
Mind you I'm only thinking shorter terms. 

13 hours ago, kerbiloid said:

They should start finding asteroids, rich with precious metals, and redirect them into the Moon.

Then harvest.

Smarter to get it into orbit so you don't have to haul it out of the gravity well, you can use the moon to capture it into an orbit. 
This would not be an stable one but that just require a little dv to fix. 

[kerbiloid]

23 minutes ago, magnemoe said:

Smarter to get it into orbit so you don't have to haul it out of the gravity well, you can use the moon to capture it into an orbit. 

Maybe, but not necessary. The Moon holds the harvester on ground for free, while in zero-g it has to constantly use engines (rocket or mechanical) to hold and to move.

So, it has to be computed, which case requires less energy per t of mined something.

Also on the Moon you can process the ore in a huge on-ground facility, which is by definition cheaper than do it in an on-board device.

***

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

Say, a car spends 10 l / 100 km, i.e. 0.07 l/km.

Say, 50 km/day, i.e. ~1 300 kg/year,

Say, the car mass is almost the same.

Then per year a car spends about its own mass of petrol.

Petrol is (CH₂)_n.

Ideally, CH₂ + 3 O → CO₂ + H2O

So, 1 kg of petrol needs 3 * 16 / (12 + 2 * 1) = 3.4 kg of oxygen.

Total annual propellant mass spent by a car ~= 4.4 * its own mass.

Mass ratio = (4.4+1)/1 = 5.4

If presume petrol-oxygen ISP*g ~=3 km/s, this means that the car could provide 3 * ln(5.4) ~= 5 km/s of delta-V,

Edited March 25, 2021 by kerbiloid

[RyanRising]

8 hours ago, K^2 said:

Same deal with surface gravity. It's high enough that you have to deal with it when building structures and sending cargo up, but too low for normal human health, meaning at best you'll have to spend a lot of time daily on special equipment keeping yourself in shape, and at worst will put a hard limit on how long you can live on the surface.

How do we know 0.38 g isn’t enough to keep away the worst health problems associated with living in decreased gravity? As I understand it, the only two data points we have for long term habitation in differing accelerations are Earth surface gravity (fine) and free fall on the ISS (not fine.) It seems to me it would be difficult to draw any any conclusions about Mars gravity beyond “it’s somewhere between the two extremes” from that. Why isn’t that the case?

[K^2]

50 minutes ago, RyanRising said:

How do we know 0.38 g isn’t enough to keep away the worst health problems associated with living in decreased gravity?

We don't. The problems might be manageable. But it's hard enough to get adequate exercise on Earth for a lot of people. If walking isn't part of your daily commute, you kind of have to find time to do at least something. At lower gravity in enclosed spaces? There is no way your daily routine will involve enough physical work if you aren't part of the construction crew. This is why I'm saying that at a minimum, physical exercise with dedicated equipment will have to be a significant portion of your daily routine. Sure, it might not kill you, but having an increased risk of early onset cardiovascular problems if you don't is bad enough. And this is best case scenario. Like you said, we only have two data points and we have pushed long duration stays in microgravity pretty far, but everything points to it not being an option for indefinite stay. Certainly, not for most people. Is a third of Earth's gravity enough to push it over into manageable indefinitely with right exercise routine? Possibly. But we don't even know that. And yes, we'll find out long before we try to establish any permanent outposts, but when the best possible outcome is significant inconvenience and worst drastic reduction to life expectancy, it doesn't fill one with optimism.

[MKI]

On 3/24/2021 at 3:00 PM, K^2 said:

An orbital station can supply standard gravity and you can even organize a miniature magnetosphere around habitable sections to give you as much protection as anything in LEO

This actually has another advantage. If your on the surface of the moon, as mentioned earlier, due to its slow rotation you end up not being able to grow much, if anything due to the long day/night cycles. However if your in orbit above the moon, you get regular sunlight off and on during your orbit. 

Mind blowing you could just build some infrastructure on the moon to build stuff in orbit above it. (orbital velocity gun, or space elevator) The idea of "catching" something using the velocity gun backwards would be straight insane, in the "my gosh that's difficult, but awesome!" kinda way hahaha.

 

Obviously radiation shielding probably becomes the biggest concern, as if your on the surface you can just dig deeper until your as safe as you need. Large scale radiation shielding would need to be "built" in orbit. If you already have the infrastructure to get stuff into orbit this becomes less of a problem, but it would probably make up the bulk of whatever long term habitat your building. (If we assume you want to shield all of it and not just some tiny part of it)

 

[K^2]

8 hours ago, MKI said:

not being able to grow much, if anything due to the long day/night cycles

That one isn't too hard to overcome. Plants grow just fine under artificial lighting. But yeah, on a station, you could end up with something like a natural day-light cycle so that you don't have to bother with lights.

It might, honestly, come down to the kind of plants you are trying to grow. Some might be more practical to grow in an underground bunker on the surface, others will do just fine in microgravity and harsh radiation of the orbital garden.

[kerbiloid]

One human requires 1 ha of plowland to satisfy all needs, or 0.1 ha of plowland to survive.

1 ha = 100x100 m2.

If replace this with hydroponics and fusion reactors, just a little smaller area of radiator panels are required in vacuum per human.

No orbital or floating plowland makes sense. No O'Neil cylinders are viable.

Orbital habitats make sense only for normal gravity.
Any farming should be placed on a much greater surface of a celestial body and be powered by sun and cooled by the plowland/greenhouse roof surface.

Any industry should be placed on the celestial body surface for same reason.

Edited March 26, 2021 by kerbiloid

[MKI]

12 hours ago, kerbiloid said:

No O'Neil cylinders are viable

Wait, why not? You'd optimally want 1 G of gravity, which requires a rather large "ring" in the first place to be rotating at that size without getting any weird issues related to Coriolis effects.

 

"Viability" in this discussion is just is more what possible with known technologies, not really the scale at which it needs to be applied. As I mentioned earlier none of this is actually possible with current funding, but non of this stuff is limited by current technology. It might be damn hard to build a mass accelerator on Moon (duh) but I don't see any hard stoppers in terms of the technology required to make it work in theory. Assuming we had such a thing (or a Lunar Space Elevator) getting stuff to orbit becomes very easy compared to fueling rockets.

 

Getting enough stuff to build an O'Neil Cylinder seems just as possible. If it makes sense just for farmland is another story. Obviously if you want an actual colony you can move, you gotta build something of that scale. If you just want food not grown on Earth, sure put it on the Moon and grow it there rather than building something in space to grow it haha.

 

 

[kerbiloid]

31 minutes ago, MKI said:

Wait, why not?

Because multiply its population by
either plowland area per human (if your greenhouse is powered from Sun),
or by area of radiator panels to emit the waste heat (if you use reactors).

Then compare this total area to the size of an O'Neil cylinder.

Quote

Each would be 5 miles (8.0 km) in diameter and 20 miles (32 km) long

Total side area  = 32 * 8 * pi ~= 800 km².

Divided by two (because petals) ~400 km².

Sunny plowland per human ~1 ha/human

Total population = 400 * 10⁶ / 10⁴ ~=40 000 humans.
Or ten times more in overpopulated case.

If use fusion instead of Sun,

A plowland receives ~1370 W/m² from Sun.
Actually, ~10 times less due to clouds, reflection, etc.
Say, you need ~100 W/m2 of your plowland.

1 ha * 100 W/m² = 10 000 * 100 ~= 1 MW to grow everything you need, not just tomatoes.

I.e. same 40 000 population need 40+ GW of electric power and should produce several hundred GW of waste heat in the closed volume.
And the active cooling system should immediately pump this heat to the radiators and require more power.
Now imagine if the cylinder population is thousand times greater.

Of course, it's a quick and dirty calculation (because it's night already), but the idea is clear.
Here on the Earth we power the crops by sun for free, and cool the reactors by ocean for free.

The O'Neil cylinder would be either underpowered or overheated.

[MKI]

13 minutes ago, kerbiloid said:

The O'Neil cylinder would be either underpowered or overheated.

That's the only explanation I'd need hahaha, but thanks for going through all the hard math, even if they are back-hand calculations.

So would that mean an O'Neil cylinder is just impossible to create and use sustainably? Regardless of technology? (besides like magical energy generation or something)

 

 

 

[munlander1]

On 3/24/2021 at 9:51 AM, Scotius said:

I wouldn't be surprised if Moon became a major source of mineral resources in the future.

Assuming the cost is only the cost to collect the materials on the lunar surface and disregarding every other cost (getting everything to the moon, getting ore/refined material back, etc.), besides helium 3 are there any elements or compounds that are rare enough on earth to warrant the costs of such an expedition?

[kerbiloid]

1 hour ago, MKI said:

So would that mean an O'Neil cylinder is just impossible to create and use sustainably? Regardless of technology? (besides like magical energy generation or something)

It means that its surface area limits it population with in the best case hundreds of thousands, while the living area is designed for many millions.

So, it means that no pressurized habitat can supply the population on its own, it can be only a habitat, while the foods should be farmed on a celestial body and use solar light for photosynthesis.

In turn, this limits the habitable zone of the Solar System with its...er... habitable zone, regardless of future technical progress.

29 minutes ago, munlander1 said:

Assuming the cost is only the cost to collect the materials on the lunar surface and disregarding every other cost (getting everything to the moon, getting ore/refined material back, etc.), besides helium 3 are there any elements or compounds that are rare enough on earth to warrant the costs of such an expedition?

The legends  of ancient scrolls say that there should be scattered platinoids and lantanoids in some impact sites, i.e. craters.

Because the terrestrial and lunar ones have sunk into core (platinoids) or uniformly dissolved in crust (lantanoids), while the asteroids (who are either core fragments, or early debris) have them concentrated.

Who knows, if this is a truth, because if it is, unlikely it would be told.

[Ethan13]

However, people are going to set up a base on the moon.

The camp will be equipped with a lunar rover that will be able to scan the terrain for water sources, a habitable mobile platform for a 45-day expedition, and a "habitat" in the form of a stationary structure that can accommodate up to 4 people at a time.

The beginning of the creation of the Lunar Base can be considered the beginning of the Gateway project.

I think this is already a rather ambitious mission.

[kerbiloid]

11 hours ago, Ethan13 said:

However, people are going to set up a base on the moon.

They do it officially since 1950s.

11 hours ago, Ethan13 said:

The camp will be equipped with a lunar rover that will be able to scan the terrain for water sources, a habitable mobile platform for a 45-day expedition, and a "habitat" in the form of a stationary structure that can accommodate up to 4 people at a time.

40 km is current upper limit of any extraterrestrial rover path. A very hostile environment.

[Ethan13]

13 hours ago, kerbiloid said:

They do it officially since 1950s.

40 km is current upper limit of any extraterrestrial rover path. A very hostile environment.

Do you mean that projects with the deployment of bases on the moon will be constantly postponed for a long time? I think so too. But I hope that Gateway and Artemis and much more will be implemented.
What will definitely not happen is a space elevator to the moon.

[MKI]

On 3/30/2021 at 12:57 PM, Ethan13 said:

What will definitely not happen is a space elevator to the moon.

If you mean a space elevator on the moon, then yea such a thing probably won't exist in my lifetime.

Heck even permanent habitat on the Moon probably won't happen in my lifetime, let alone building such a creation.

 

The only chance I'd see if happening is if Elon suddenly pivots and focuses on the Moon for this specific goal lol.