Remind me when a human steps foot on the moon again right next door.

Fair, but I'm less concerned about footprints, and more about economic complexity in space. None of our engineering base was designed for off-world use. We not even recycling old satellite hulls yet...

We're so close. We have 3d printers that print metal... We have solar panels, computers, algae that excretes gasoline... Every piece needed to create a basic colony in space, we have. I don't mean on Mars... Just space. It would be beyond silly to escape the gravity well just to go down another for no good reason. Forget the moon. We need water, so the correct target is some comet coming nearby. Catch it, park it in orbit of a nearby asteroid - that's the start of an industrial base. Then we begin the slow march into the deep void, grabbing ice and uranium wherever we find them.

Hell yes! Two reasons to go back down a gravity well, and they're actually one. Gravity is useful for so many forms of material separation - you can't even do a reflux still without gravity. You can cheat with centrifugal force, but then you need to maintain those bearings and structural elements because the failure modes really aren't nice. Secondly, and the big one - undifferentiated rocks and ices are nearly useless to us. Even on Earth, mining depends on finding places where a natural energy gradient has done most the hard work for us already concentrating whatever we're after. Mars likely has ~90% of the ore minerals found on Earth, some deposits having purities not seen here since the Bronze Age. Europa and Ganymede have much stronger energy gradients than Mars ever had. Their geology is WEIRD, but if we figure it out its industrial heaven. Luna is quite useless, and the Main Belt asteroids not much better. Water ice and iron-nickel alloy being the only resources of value.

Ganymede is a prize, and I've said before that I claim it for myself, and I'll keep saying until I can plant my flag on it and then keep saying it. There's more water there than on earth... The benefits of gravity can be had without landing on a planet. Theoretically, you could walk on a satellite that's in geosynchronous orbit. I don't think anyone's tried it yet... But assuming that's true, and I think it makes sense you could have the refining job in orbit and still pay a fraction of the cost that it would cost to get out of an atmosphere. That also makes sense because transport of ores is better done as a stream of pellets into a receiving orbit than as a spaceship with cargo.

Cost of escaping a gravity well is proportional to the square of its escape velocity plus atmospheric friction. Ganymede and Europa are pretty sweet there, there are many ways to get those ore pellets into orbit from them. Mars would still suck, albeit dramatically less than Earth, but it almost certainly has REEs, PEMs, gold and silver that you won't find accessible on the Jovian moons. I like this plan. Calling dibs of Europa, then :D #space #spacecolonisation

Excellent! We shall be competitors for refueling the solar system! Friendly competitors... Maybe cornering the market

I think large scale space colonies, O'Neil colonies at GEO and beyond laregely build from near earth asteroid material is the way to go. 2 mile by 10 mile or so rotating cylinder. Earth normal inner outer edge gravity. Variable gravity toward the center. Solar mirrors for light and much of heat. Much better than being on some rock not at all fit for human habitation like the moon or Mars. Of course first step is a doozy. IMHO we need lots of space robotics and nuclear space tugs to change down near earth asteroids to get it done. Can't do it with humans in space alone as we are fragile, especially outside van Allen belts, until a lot of supporting space infrastructure is in place.

Spin up gravity when you need it on a large enough space station and have the advantage of microgravity or none when that is best for what you are doing. Lots of differentiation of material in asteroids and half mirror solar furnance in inner solar system can provide a lot of process heat on demand. Asteroids are not at all useless. Best nickel deposit on earth I hear was from an ancient metallic meteor hit. BTW the metallics have a lot of very high priced precious metals that would be darn useful for funding the rest of what is really needed for space development.

Nuclear is definitely the way to go. And long term, O'Neil cylinders are, too. They're just expensive... Before we get to that stage, we'll need gravity without the cost of going back to earth, which is why I think we'll need to build habitats in geosynchronous orbits.

So... We should catch Apophis in 2029?

Spinning is unfortunately not simple, especially if you have a number of different processes going on producing different torques and a moving center of gravity. Pumping liquids between tanks is the most elegant solution, but still not simple or lightweight. Then you have to station-keep whilst under the gravitation influence of multiple bodies whilst shipments are arriving and departing, imparting various momentums and torques. Can be done, just math and lots of propellant. Solar furnace I'm not fond of - throughput is lol-worthy small, and you have wear and tear on seals. You're absolutely right re nickel, but I'm unaware of any asteroid deposits of native precious metals, I understand they're all likely alloyed with nickel and iron. They could be separated out, my boss is a big fan of nickel carbonyl solvation. But huge capex and unattractive energy cost, and ongoing leakage of process gases. I fear asteroid mining is something of an "altcoin", to put it politely.

Large scale is the way to make things economic, for sure. Leakage of atmosphere per unit volume is better for a start, and the problems of slosh and of asymetries of rotation causing varying centripetal force, vibration and cascading failure are much less dangerous at scale. The only asteroid materials we're going to be refining in bulk any time soon are nickel, iron and water, but it so happens they're what is needed for this :) Radiation environment sucks for humans, even for robots, but sufficient bulk between you and the outside will cut it down. My only real concern with O'Neil Cylinders is how they will pay for their inputs. Manufacturing? Mining colonies on some moon can sell raw materials, even if the logistics chain is a decade long. But manufacturers in free space are in competition with Earth (for the high-end stuff), and with the mining colonies (who will want to fab some least-complex stuff themselves).

Earth's gravity is still substantial at GEO, but in any stable orbit it will be balanced by an equal centripetal force. Not useful for material separation, sadly

Ah, well, there's always spinny things then

But people will still need places to live, and microgravity is unhealthy

Are the Psyche asteroids' ores pure enough to count? Last I heard, there's enough gold up there to make gold a shitcoin, and if there's gold, maybe there's other rare metals

Psyche's ores are about as pure and noble as the US Congress. With enough energy and the use of toxic process gases, sonething useful might be made from them. But without "new physics", we won't be separating asteroidal gold economically enough to compete with terrestrial planet production, ever, never mind make it a shitcoin.

Microgravity is definitely unhealthy, but last I checked we still have no idea what fraction of g is required for maximum health. I should check if any of those centrifuge experiments on the ISS shed any light...