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Comment by maxerickson | Hacker News Reader

The real answer is to figure out some interesting or profitable activity that you can do there and then let the details take care of themselves.

Of course the government could pour massive resources into it to see what happens, but we aren't really at the point economically or technologically where that makes sense, at least in my arrogant opinion.

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We spend tens-of-billions of dollars each year putting satellites in space. About $6B just putting fuel into LEO to lift things to GEO, so delivering fuel to LEO is a good starting point and I think we can eventually consider doing a suborbital rendezvous with a rocketship already fueled from lunar sources. Lunar gravity is low and there is no atmosphere so it is likely that in the long run the majority of material used in space will come off the moon or asteroids. A coil-gun would only need to reach 2km/s to get to an L1 transfer station to process materials into satellites.

Seems like we should achieve ISRU with robots before we waste a lot of money to send people.

Isn't that a little tautological? You rightly observe that there are uses for LEO and GEO, but you are responding to a question asking "what can we do on the moon?" with "well, we can put propellant in cislunar space so we can do stuff on the moon."

I think you put the cart before the horse here. Back in the 1400's, people were going out on ships to explore planet earth backed by monarchs on the assumption that there would be resources to exploit once they got there. I think the assumption here is that first we establish a colony on the moon, and then find a profitable activity.

That's not how colonization happened though. They went to exploit obvious riches, not to see if they could find something to do.

And the early colonies were plenty underplanned and disastrous.

Also, that's what my second paragraph is about. Given our current resources and capability, an experimental colony is a fool's errand.

There were other differences. In those days, they were colonizing places where they could easily adapt their existing ways of life. Their technological base was small enough that the colonies could become relatively self-sufficient quickly.

None of that would apply to a colony on the Moon: surviving there would require advanced technology, and we don't know if it's even possible for humans to survive in such low gravity for an extended period. A colony would probably remain dependent on Earth to supply manufactured products, such as semiconductors. Modern society uses a vast range of products. It probably wouldn't be much more self-sufficient than the ISS, and it wouldn't survive if Earth lost interest in supporting it.

It wasn't particularly easy to adapt. Lots of people died and it took decades to get footholds.

I've read about some of the early British colonies in Australia, and doesn't seem to have taken long before they were laying out farms, making bricks and quarrying stone blocks, constructing solid buildings, setting up blacksmiths, newspapers, etc. But by then it was getting into the 19th century.

Compared to the moon, it was stupendously easy. There was air to breathe, water to drink, and plants to eat, and reasonably safe levels of radiation. So easy even a caveman could do it.

The only thing the moon has going for it is the apparent absence of microorganisms that cause human disease.

Yes, of course humans already colonized most of the world in prehistory. Even remote Pacific islands had been colonized before 1000AD.

although i hate it, yeah. there are plenty of places humans don't live _on earth_. Deserts and tundra are obvious. but like 70% of the surface is water, and basically 0% of the population lives there.

Maybe we need to go down before we go up. Maybe we need to survive at a few meters below sea level before we can handle living at a few kilometers above it.

Yes, I think even building a completely self-sufficient city in a desert on Earth, with the ability to build its own equipment including computers may be beyond us at this point. Obviously it would be a lot easier than doing it on the Moon or Mars, but too much of the technology that would be needed is locked up in trade secrets.

There's plenty of 3D space available at the surface of the Earth; it's not exploited either because it's not profitable or because government rules prevent it. Who wants to live in a desert in the middle of nowhere? But they want to live on Mars? It would get old fast, especially with such a laggy Internet connection.

Here's the thing: In the 1400's there were fundamental differences in the general understanding of how the world works.

On top of that, the only problem left to solve was range of movement, in terms of thousands of miles and months at sea, using proven technology, typically utilized not too far from a coast with a known port. Diseases, hostile locals and natives, food supply, the return trip, all were considered otherwise negotiable concerns.

The moon, on the other hand, comes with at least two major problems:

1. Extended side effects of long term exposure to low gravity, within the context of human health.

2. Sustained self sufficiency for resource usage, and sociological organization of an encapsulated non-terrestrial community, with no regimented military context.

So, what would the age of exploration look like, if you were to add those two problems onto the problems already faced?

Your point 1 is why I expect any colonies on the moon and mars to stay as short-visit research colonies with any installed industry being as automated as possible. Long stay off-world colonies will be actually off-world. They will be spinning orbitals with public habitat around 1G.

I'd also expect biology research to start to change this calculus before physics research does, as we are likely to be able to engineer humans to put up with low gravity environments sooner than we will be able to engineer a gravity field.

Uh, no. In the 1400s, the maritime powers in the western fringes of Europe were attempting to build seagoing routes to modern Indonesia and Australasia that bypassed the Venetian and Ottoman trade monopoly, and aimed to use their sea power (mostly, fast sailing ships with guns on board to shut out potential competitors) to do so. Columbus argued that it was easier to cross the Atlantic Ocean to do so, but had a bad map and underestimated the size of the Atlantic. He was saved by the fact that there happened to be another landmass where he thought China was instead, and there wasn't much interest or activity until people realized that the natives were literally covering their houses with money (at least, what the Europeans thought of as money--the natives didn't think the same way), and, well, the rest is history.

Assumption? It was mainly to compete with the Silk Road, India was known.

Moon hotels. Tell Trump he can put his name on it and we'll have them in no time. But seriously, if the safety issues with space travel are reduced to a minimum, and we figure out how to make that whole escape from orbit thing a bit cheaper, I think this is the first interesting activity that people would pay money for.

EDIT: Honestly if someone is downvoting me because I mentioned Trump in a non-partisan fashion, that's rather petty.

I was close to down voting not for trump but for "more rockets for moon tourism". We are already messing up our planet with air travel. IMHO, make moon tourism a thing, with the associated rise in rockets launched, and rockets go from "amazing tech that sciences" to "yet another thing super rich people use for enjoyment while fucking over literally the entire planet"

From what I understand, the amount of stuff rockets carry into literally every layer of the atmosphere is already concerning. If someone can put my mind at ease with a paper not written by Big Rocket I'd be all the happier. ;)

"From what I understand, the amount of stuff rockets carry into literally every layer of the atmosphere is already concerning. If someone can put my mind at ease with a paper not written by Big Rocket I'd be all the happier. ;) "

Not an expert, but I believe the Saturn moon rockets did run on hydrogen, so there should not have been much pollution. The falcon-9 though runs on RP-1, refined kerosine.

The Saturn V only used hydrogen for its third stage. The first two stages (i.e. the ones that operated while it was still in the atmosphere) ran on RP-1.

Are there fundamental flaws with using hydrogen in the atmosphere?

Too volatile to handle?

The Delta IV Heavy uses hydrogen fuel even for the first stage:

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

Hydrogen offers excellent ISP but poor volumetric energy density, and it needs to stay much colder than oxygen to remain liquid. Fuel tanks for containing hydrogen tend to be more complicated and larger than those for other liquid rocket fuels. Upper stages see more relative benefit from the higher performance achievable with hydrogen fuel. The cost:benefit comparison has led to most rockets not using hydrogen for the first stage.

Thanks dor the detailed explaination!

But I assume

"The cost:benefit comparison has led to most rockets not using hydrogen for the first stage."

nobody factored in the long term climate cost with kerosine. But since most hydrogen is generated with fossils, it might not make a big difference right now.

Hydrogen yields higher efficiency (specific impulse) with lower thrust. Larger-molecule fuels, such as kerosene, have higher thrust and lower efficiency. When in the atmosphere, the rocket engines are spending a lot of energy counteracting gravity, so higher thrust is important. Once in orbit, efficiency is far more important (indeed, some deep space engines such as ion engines produce only millinewtons of force, but are very efficient.)

Consider that the moon hotel would enable Moon solar power plant

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