If you could setup a permanent base on the moon....

[gomipile]

If you're mining asteroids for resources, why would you fire those down into the Moon's gravity well so you have to waste fuel lifting them back out again?

The same reason that most new nuclear power plants use boiling water reactors instead of pressurized water reactors despite the fact that PWRs are safer and cheaper to operate and maintain, among other advantages. Initial cost of construction.

It would cost a lot less to fly construction equipment to the Moon and build a base buried under 10m of regolith than to build a spinning orbital habitat with an equivalent amount of radiation shielding. That initial cost savings would be multiplied by the size of base you want.

Say you want an industry which would work best with a company town of minimum 5000 people total including supporting professions like education, health care, child care, etc. The initial cost of that 5000 person lunar base would be peanuts compared to an O'neill colony of similar capacity. Yes, the O'neill colony would have lower process costs and higher yearly net profit, but it would take much, much longer to break even and start turning a total net profit.

[Fat Rooster]

The main reason to use the moon would be availability of 'stuff'. For most purposes being in orbit would be better, but getting large masses into orbit is far easier from the moon than from earth. If you want a giant solar array set up in space it makes sense to get the silicon from the moon, provided you are also able to get rocket fuel from the moon too. Even if the differences are marginal, a case could be made for not using earth based launches due to nitrogen oxide concerns from re-entries. It might prove to be the landmark decision on whether we put the earth above all other objects in terms of protection status; whether marginal damage to earth is acceptable when the same can be achieved by exploiting another object. Doing damage during the transport of people might be fine, but moving fuel into orbit might not.

I don't actually see the duty cycle of solar being that much of a problem, because you need to transport energy anyway. For you to have access to water, you need to be placed out of sunlight. You get water or energy, but nowhere both. A vertical solar tower at the poles would be possible initially, but doesn't scale nicely because of structural constraints, and even then you need to transport energy from the rim of the crater to the base. Once infrastructure is set up this becomes less of an issue. Aluminium cables can be run on the ground without any insulation, and while cables thousands of kilometres long would take a long time to produce, all it would require would be energy and local materials (aluminium is available basically everywhere). A rolling factory could be perpetually connected to a large solar station nearer the equator as it extrudes a cable. Chances are that you will be able to produce large quantities of silicon as a biproduct, so producing the solar stations from the same factories might be viable. Similar rolling factories could run loops along latitudes, so by the time you are getting any energy transported long distances the duty cycle becomes an inefficiency rather than causing actual intermittency of power.

In the medium term, the main advantage of lunar construction would be that a space elevator would be feasible, making lunar material by far the cheapest option. A lunar colony could be bootstrapped from a solar and cable producing rover and a strand of a lunar elevator even without the use of rockets.

Saying the moon doesn't have heavy elements is a bit of misnomer. It has about as much as earth's surface, they are just distributed differently. Most of the iron from the formation of the earth is locked up in the core, as is any element with an affinity for iron. The stuff we have access to almost all comes from later impacts, and the moon doesn't fare much better than the earth. Where the difference comes is from liquid water, plate tectonics (possibly also from liquid water), and life. Geological and biological processes on earth have concentrated certain elements over very long timescales. While different processes might exist on the moon with such concentrating effects, we don't know of them (though we wouldn't). It is similar to the rare earth elements here. They are not particularly rare when considered as a percentage, with niobium and neodymium being more common than lead, and almost as common as copper. What is rare is high quality ores. We can still access them by strip mining and processing huge quantities of material, which we might be doing anyway.

As for why we should do the Moon over Mars as our first colony; flexibility meaning planning does not have to be nearly so perfect. If we find out that we have made a mistake in our plan, getting additional equipment to the Moon is far easier. A failure that means everybody dies in 2 weeks is recoverable on the Moon. This is important, because it means that food is not survival critical and food is far harder to get working than water or air. Missions can be set up with abort modes that do not require the refuelling equipment to work, and work from day 1. We can learn things practically on the Moon that we would need to theorise about if we went to Mars, and that is always slower and less reliable than simply trying something out. Given that the two big unknowns would be food production and ISRU fuel production, the fact that we can set up a Moon base with current tech that does not rely on these two things is massively in it's favour.
The other big advantage the Moon has is turn around time. If we try something on the moon and it doesn't work, we can have the MK2 there in a fortnight. Mars would have a turnaround time of years. As Elon says about timelines, "if it's long it's wrong".

[factotum]

Yes, having the Moon as being a dry run for testing survival techniques that would be required for deep space colonies is certainly a valid reason for setting up a colony there--although, in that case, you'd have to be severely limiting the usage that you made of any local resources available, because those same resources won't necessarily be available on, say, Mars.

[jayem]

Yes, having the Moon as being a dry run for testing survival techniques that would be required for deep space colonies is certainly a valid reason for setting up a colony there--although, in that case, you'd have to be severely limiting the usage that you made of any local resources available, because those same resources won't necessarily be available on, say, Mars.

Although: If you've done dry runs with respect to a few resources (and say are really confident with establishing energy) at least then you can put the effort onto thinking about how you deal with metal. So even if you 'cheat' it's still a step in the right direction and valuable knowledge.
So long as you remember that you've done it, of course.

[The Random NPC]

Get permission from who?

Also, the moon is big. Like, it's a lot smaller than the earth, but it's still very, very, very big.

I think, like Antarctica, you'd have to get permission from all the major powers.

[halfeye]

I think, like Antarctica, you'd have to get permission from all the major powers.

I suspect getting there is all the permission you currently need. If there is a major presence already there or in the space around it in the future, then they might have something to say, but they'd probably need weapons to make anybody take any notice of what they were saying.

[factotum]

I suspect getting there is all the permission you currently need. If there is a major presence already there or in the space around it in the future, then they might have something to say, but they'd probably need weapons to make anybody take any notice of what they were saying.

Might Makes Right hasn't actually been a viable method of international diplomacy in quite some years now. I imagine, if anyone started to set up a moon base for mining there, the signatories of the Outer Space Treaty would have to have some discussion and the treaty would need to be updated to reflect that--at the moment it's fairly unclear on the subject of lunar and asteroid mining.

[DeTess]

Might Makes Right hasn't actually been a viable method of international diplomacy in quite some years now. I imagine, if anyone started to set up a moon base for mining there, the signatories of the Outer Space Treaty would have to have some discussion and the treaty would need to be updated to reflect that--at the moment it's fairly unclear on the subject of lunar and asteroid mining.

Yeah, though either that treaty, or another one of the major space treaties (I don't quite remember which one of the top of my head) does in fact have a provision for when asteroid mining or mining the moon is about to become viable, though all it says is that such a situation would require a revision and making a new treaty, which isn't that helpful.

Still, I happen to know for a fact that work on this new treaty is in progress, though it obviously isn't a particularly high priority (though that will likely change once the first commercial venture starts bringing stuff back). Several countries, including most notably Luxemburg and the USA have passed laws that basically make it legal for companies based in said countries to harvest resources in space for profit, though these laws are not entirely in line with the Outer Space treaty.

[halfeye]

Might Makes Right hasn't actually been a viable method of international diplomacy in quite some years now.

I sort of wasn't talking about might making right, I was talking about being there making it okay to be there when nobody else was already there. I can see it's sort of similar, but there's not exactly a lot of martial might involved.

In a slightly longer view, I would foresee any lunar settlement eventually becoming independant of all Earth based nations.

[Peelee]

For almost a decade now I've beg saying that Space Law is about to be an in-demand field.

[The Random NPC]

I sort of wasn't talking about might making right, I was talking about being there making it okay to be there when nobody else was already there. I can see it's sort of similar, but there's not exactly a lot of martial might involved.

In a slightly longer view, I would foresee any lunar settlement eventually becoming independant of all Earth based nations.

Yeah, but as pointed out, there's a space treaty. If you ignore everyone it can result in anything from everyone ignoring it (unlikely), to trade embargoes/higher tarrifs (more likely), or even war (very unlikely). I'm sure there are other responses as well.
EDIT: Also, I hope space law is at least as interesting as tree law.

[Peelee]

Yeah, but as pointed out, there's a space treaty. If you ignore everyone it can result in anything from everyone ignoring it (unlikely), to trade embargoes/higher tarrifs (more likely), or even war (very unlikely). I'm sure there are other responses as well.
EDIT: Also, I hope space law is at least as interesting as tree law.

Space Law is actually a full branch of law. Two universities in the US specialize in it during law school, IIRC University of Mississippi and one of the Dakotas, I wanna say South? But yeah, all the treaties are from the space race and are nearing 70 years old, with a lot of assumptions that didn't really pan out and various changes now, like corporations having robust space programs (even if they do almost entirely contract through the government agencies). Also ESA is getting big, and the Chinese, Japanese, and Indians are in the game as well. Lots of fertile ground for new treaties, new laws, and forging new ground in general.

Plus,you get to call yourself a space lawyer. Which is just awesome.

[Traab]

I honestly consider it a bit of a coin toss as to how treaties might go. The biggest issue being potential profit and increase in power. If, for example, we discovered that 50 feet below the surface the moon is actually made entirely of an odd mix of gold and oil, there would be a LOT of hullabaloo over who gets to go there and dig for it as it would represent lord knows how much gain for whoever manages to lay claim to it. If the moon is a barely tolerable stop gap location for further space expansion, in other words, only just better enough than earth itself, and has little to no resources worth arguing over, then there isnt likely to be a large amount of strict regulation and a more ad hoc agreement to let other nations use the base if they want to try their hand at deep space missions too. And of course there is always the potential military applications. My moon base needs to have a space laser after all, otherwise, whats the point? That tends to make people get all objectionish about my plans though. "Wah wah wah! You might blow up my nation and I wouldnt be able to stop it! Blah blah blah! I dont WANT to pay you billions to point your laser elsewhere!" You know, little things.

[halfeye]

If, for example, we discovered that 50 feet below the surface the moon is actually made entirely of an odd mix of gold and oil, there would be a LOT of hullabaloo over who gets to go there and dig for it as it would represent lord knows how much gain for whoever manages to lay claim to it.

Actually, I suspect you'd find gold isn't worth enough to ferry from the moon, and oil certainly isn't. Platinum, if you didn't find too much and crash the market might be, and diamonds and sapphires might be if we weren't already making them.

[factotum]

Actually, I suspect you'd find gold isn't worth enough to ferry from the moon, and oil certainly isn't.

Oil might very well be, actually, because if you can build a refinery on the Moon to distil the stuff into rocket fuel, you have a ready-made method of getting it into space. Getting it safely down to the ground at the other end would be more of an issue, of course...

[halfeye]

Oil might very well be, actually, because if you can build a refinery on the Moon to distil the stuff into rocket fuel, you have a ready-made method of getting it into space. Getting it safely down to the ground at the other end would be more of an issue, of course...

Well yeah, I meant ferry down to Earth. If there was any up there, which is almost impossible, then using it up there would be perfectly feasible. Space travel is very expensive, and getting down to Earth safely is nearly as hard as going up to space.

[Traab]

Ok but still, you get my point. There is the vast range of value potential in the moon that would determine what sort of treaties would be formed. If its the equivalent in value of a truck stop for space travel? No big deal, probably a fairly casual "Let us use it too when we want and we will kick in a few bucks to help setup" sort of deal. If it turns out the moon is valuable for more than just easier liftoffs into deeper space things will get more complicated.

[halfeye]

Ok but still, you get my point. There is the vast range of value potential in the moon that would determine what sort of treaties would be formed. If its the equivalent in value of a truck stop for space travel? No big deal, probably a fairly casual "Let us use it too when we want and we will kick in a few bucks to help setup" sort of deal. If it turns out the moon is valuable for more than just easier liftoffs into deeper space things will get more complicated.

My understanding is that at this point there's not expected to be much there except rock, and maybe some very desirable water at the poles. It would be a very useful truck stop, truck stops do a lot of business.

[Peelee]

If there was any [oil] up there, which is almost impossible

I see my theory on space dinosaurs is already meeting resistance.

[Tvtyrant]

I see my theory on space dinosaurs is already meeting resistance.

The whole notion leaves me breathless.

[Fat Rooster]

My understanding is that at this point there's not expected to be much there except rock, and maybe some very desirable water at the poles. It would be a very useful truck stop, truck stops do a lot of business.

No need to sell rock short. Rock is largely silicon, and you only need trace amounts of other elements to make that into solar panels, and other electronics. Another major constituent is aluminium, useful for conductors, as well as structure. By far the most relevant element is oxygen though. A hydrogen engine only has ~12% of the propellant mass as hydrogen, with the rest being oxygen. Even without the water a useful percentage of propellant is available pretty much anywhere.

With aerobraking, it is possible to refuel hydrogen in LEO, land on the moon, refuel oxidiser, and bring a cargo mass of oxidiser back to LEO greater than the hydrogen refuelling (and keep cycling). It can be cheaper to bring oxygen to LEO from the moon than from earth, and that is worst case scenario. An oxidiser supply at the lunar gateway would be even better for long distance travel, with a ship refuelling oxidiser in LEO, then going to the gateway, and then going from there by slingshotting past the earth. You can avoid much of the tyranny of the rocket equation if you only have to carry the hydrogen with you.

It would be like a truck stop that sells fuel at half the price, it could be a really big deal.

[factotum]

Hydrogen isn't a great choice for a fuel when you're looking at long duration missions, though, which is presumably why we're looking at going beyond the Moon in the first place. It has to be kept very very cold in order to not evaporate, which is something you really don't want to happen--your turbopumps will not be happy if they swallow a large gob of hydrogen gas rather than the expected liquid hydrogen. You would be better off with a chemical propellant that's stable at higher temperature, or else you'd want to be using ion drives, which prefer stuff like Xenon as a propellant.

[halfeye]

Hydrogen isn't a great choice for a fuel when you're looking at long duration missions, though, which is presumably why we're looking at going beyond the Moon in the first place. It has to be kept very very cold in order to not evaporate, which is something you really don't want to happen--your turbopumps will not be happy if they swallow a large gob of hydrogen gas rather than the expected liquid hydrogen. You would be better off with a chemical propellant that's stable at higher temperature, or else you'd want to be using ion drives, which prefer stuff like Xenon as a propellant.

How cold is it in the craters near the poles where the water ice is? could you maintain liquid hydrogen there without refridgeration? I'm not that convinced on hydrogen being an asset, but if it's easily available we might as well use it.

No need to sell rock short

Rock is good, and I was in no way implying that it isn't. It's great for building structures, either in concrete or by making holes in pre-existing masses (we might well need to make the holes airtight afterward). I'd expect that a moon base would be mainly built out of moon rock.

I'm not at all sure that fractioning rock to get at the elements they contain is a good idea in a vacuum, they tend to be resistant to that until you involve high temperatures which are inherently dangerous, and in an extremely hostile environment like the moon, avoiding unnecessary dangers is usually preferable. Once everything is set up and running smoothly, maybe, but I'd want the truck stop to be operational for a couple of Earth years at least before thinking about that sort of complication.

[Fat Rooster]

Hydrogen isn't a great choice for a fuel when you're looking at long duration missions, though, which is presumably why we're looking at going beyond the Moon in the first place. It has to be kept very very cold in order to not evaporate, which is something you really don't want to happen--your turbopumps will not be happy if they swallow a large gob of hydrogen gas rather than the expected liquid hydrogen. You would be better off with a chemical propellant that's stable at higher temperature, or else you'd want to be using ion drives, which prefer stuff like Xenon as a propellant.

Firstly, things are far easier to keep cold in space. The difficulties with storing hydrogen on earth are the requirement for large vacuum vessels for Dewar flasks, and the supporting structure required for the weight, both of which are trivial in space. Secondly, most of the delta v to get anywhere (except maybe Jovian moons if you are in a hurry) is going to be spent close to earth within a few days of launch. Even if you use a different propellant at the other end you can still use hydrogen for the majority without having to store it.

Ullage motors are not specific to hydrogen, and are actually less of a problem for hydrogen than for most other fuels. The low density means that the pumps care less if a bubble goes through, as the relative masses of the compressor to fluid is much higher, and expander cycle engines actually start to develop thrust before the compressor even starts up.

High temperature propellants are definitely simpler, but if you are getting the oxidiser to orbit cheap it's advantages are further amplified. We are still at the point of 'just get there', which means do whatever works. The Elon Musk approach of 1 engine to do everything is a great phase 1, but phase 2 will be more specialised tools, and that means hydrogen once we are off earth. The use of methane has advantages is specific to mars, because of the abundance of CO2, but fuel is not available everywhere, while oxidiser is.

[Telok]

Hydrogen peroxide has been used as a monopropellant. Still just O and H but easier to deal with than straight H. A bit less oomph than a liquid O/H engine but also simpler for being a mono.

Really it's all doable. Just engineering challenges and the will to pay for it.

[factotum]

How cold is it in the craters near the poles where the water ice is? could you maintain liquid hydrogen there without refridgeration?

Not even close. The temperature in the "cold traps" (e.g. the permanently shadowed areas inside craters at the lunar poles) is around -121C. That's cold, but it's nowhere near cold *enough*--you couldn't even maintain liquid oxygen at that temperature (boils at -183C), and liquid hydrogen requires -253C, only 20 degrees above absolute zero.

@Fat Rooster: I'm just going by what has been actually used in long-duration space missions before. Probes designed to spend years in space, like Voyager and New Horizons, use hydrazine propellant, because it's a heck of a lot easier to store than LH2--and when you consider both those probes spent most of their time in the outer Solar System, a long way from that big fusion reactor that causes all the problems, you have to ask why they didn't use LH2 if it's such an obvious and easy solution.

[Peelee]

Not even close. The temperature in the "cold traps" (e.g. the permanently shadowed areas inside craters at the lunar poles) is around -121C. That's cold, but it's nowhere near cold *enough*--you couldn't even maintain liquid oxygen at that temperature (boils at -183C), and liquid hydrogen requires -253C, only 20 degrees above absolute zero.

It's very handy that the coldest known places in the universe are on Earth, then.

[Tvtyrant]

It's very handy that the coldest known places in the universe are on Earth, then.

There are cooling jackets and vests which are basically blue ice capsules sewn into clothing for temporary cooling effect.

[Fat Rooster]

Not even close. The temperature in the "cold traps" (e.g. the permanently shadowed areas inside craters at the lunar poles) is around -121C. That's cold, but it's nowhere near cold *enough*--you couldn't even maintain liquid oxygen at that temperature (boils at -183C), and liquid hydrogen requires -253C, only 20 degrees above absolute zero.

@Fat Rooster: I'm just going by what has been actually used in long-duration space missions before. Probes designed to spend years in space, like Voyager and New Horizons, use hydrazine propellant, because it's a heck of a lot easier to store than LH2--and when you consider both those probes spent most of their time in the outer Solar System, a long way from that big fusion reactor that causes all the problems, you have to ask why they didn't use LH2 if it's such an obvious and easy solution.

It is not easy, and brings a fair amount more complexity, so the benefits have never been worthwhile before. No deep space probe has ever run badly into the tyranny regime so more efficient propellants simply haven't brought enough benefits. For reference, Cassini* could have gotten a similar delta v from 2 tons of hydrogen oxygen, as opposed to 3 tons of hypergolics, bringing the launch mass from 5.6 tons to 4.6... except it wouldn't. On top of the temperature difference, hypergolics have a much higher density, meaning pressure fed is viable. You also don't need an ignitor. When designing a probe you can either design your own system that saves 1 ton of launch mass, or buy an off the shelf R4-D which is going to be simpler, tried and tested, can be fuelled before integration with the rocket, doesn't need to worry about earth's atmosphere, and can also run off the same system as the manoeuvring thrusters. The money saved can go towards a bigger rocket.

Voyager and new horizons in particular barely had engines at all. I think they had ~500m/s in the manoeuvring system for fine adjustments, but unless you are slowing down somewhere you don't need significant burns. Manned exploration will be wanting to slow down and probably land somewhere, which means a much higher fuel percentage (if there is no atmosphere). Personally I would love to see what the Geology of Io has produced in terms of ores, especially given the near infinite energy available there.

Another consideration is orbital fuelling, which was never used for probes. A storage tank optimised for vacuum will not work on earth, but this isn't a problem if you are going to fuel it in space (and deal with the small losses from a foam insulated tank for getting the hydrogen to orbit). You can just send your long term storage tank up empty, and fill it later. For a probe this would mean 2 launches rather than one, but most of the manned profiles we are looking at currently already require orbital propellant transfers.

For a real life demonstration that it can be done, we can look at the Hershel space observatory. It used ~300kg liquid helium to cool it's instruments (boiling it off), and it lasted 4 years. I expect there were quite a few headaches getting that to work, and the engineers were not even sure how well it would work (they underestimated the lifespan by a year).

It is slightly inaccurate that hydrogen isn't used, because many probes have flown on centaur upper stages, with that doing most of the work. Where hydrogen has not been used we typically have done multiple Venus gravity assists that would not be viable for manned missions because robots are more patient than people. The point I was making was that a hydrogen engine could pause in LEO to refuel with oxidiser from the moon and savings could be made. You could then refuel again out around lunar distance, before doing a final burn as you fly past the earth. There is a way around the tyranny, and at some point it is going to be worthwhile to build the infrastructure to use it. None of this even requires storage for more than a few days to be extremely helpful.


If you ask the question "what is the best way to get 100 manned spacecraft to Io" you might get a very different answer to "how do I get 1 small probe to Jupiter". It is not that the people building the probes were wrong, they were just asking a different question*. A large colonisation effort might make setting up complex intermediate infrastructure on the moon worthwhile, where supporting individual probes obviously does not. The complexity of the design of the spacecraft becomes a smaller part of the cost, so that an attitude of "just go with what we know works" isn't so efficient. It is better to spend a bit more on development, to the point of blowing up prototypes that would double the cost of a single item product. For each manned lander on Io you could potentially be saving hundreds of tons into orbit, and at that point those 50%+ launch cost savings from only having to launch the hydrogen really start to look worthwhile. The main factor in this is what mass fraction of a propellant mix is oxidiser, which hydrogen wins out on handily. The high specific impulse is actually just a bonus.

*For reference, Elon Musk is asking "what is the fastest way to Mars". Setting up infrastructure will make it cheaper, but we don't actually need it for Mars. Aerobraking both ends mean the rockets don't need to be that big. Mars has the resources to make methane, in a way we already know about. In contrast, getting the oxygen out of silicate minerals without carbon is a relatively unexplored problem as far as I know, because it isn't ever needed here on earth. The really cool thing about this is that it can drive the development of lunar infrastructure, because the mission profile already calls for orbital refuelling. Potentially they could start buying oxidiser in orbit, driving commercial oxygen production. That same tech could also be used on Phobos, lowering the fuel requirements to get back from Mars further.

[factotum]

The main factor in this is what mass fraction of a propellant mix is oxidiser, which hydrogen wins out on handily. The high specific impulse is actually just a bonus.

Hydrogen loses quite badly in terms of bulk, though--they didn't use LH2 in the first stage of the Saturn V, where efficiency gains would likely have mattered the most in terms of total fuel usage, because the required fuel tank would have simply been too big. The point about oxidiser does raise a question, which is: what oxidiser are you most likely to be able to find on the Moon? I don't think we actually have an answer for that. If oxygen is in short supply, but nitrogen and hydrogen are relatively plentiful, then hydrazine becomes a much better option for your rocket fuel than LH2--it might be slightly less efficient, but because it's available in much larger quantities it offsets that. I don't think we'll have a final answer for that until we actually have a moon base set up where people can do mining operations to find out what's beneath the surface, which brings us back to a reason for building the thing in the first place!