What would it take for humans to have a successful colony off Earth? That's a big question, but I have a few thoughts.
Whether you're talking about Luna, Mars, Venus, asteroids, or somewhere else, space is a very hostile environment compared to Earth. This means that more stuff per person is required to survive. So, the economy of a space colony must have more wealth per capita than the economy of Earth.
Yes, much of the economy of the modern USA goes into luxury and signalling. Yes, having exceptional people would improve the productivity of a colony compared to countries on Earth. But on the other hand, minimum scale is a big problem.
The modern economy operates on a large scale. Most "economic progress" has involved greater specialization and centralization. Many specialized but key products are only made at a few locations. Chemical plants, semiconductor foundries, and many other things have gotten bigger and more expensive. Even fairly large countries need to trade with other countries for key items.
I estimate a minimum scale of ~100M people for something like the current economy. A colony in space would be far smaller, and economic productivity at that small scale is usually a very different problem than productivity on the scale of a billion people. As such, most progress on industrial development is not applicable to a space colony. So, development of new manufacturing techniques for high productivity on a smaller scale is necessary for a successful space colony.
What new techniques are needed, specifically? 3d printing? No, I don't actually think 3d printing is very helpful. It's mostly a replacement for injection molding, which is easy. If you look at some video of, say, an assembly line for truck production, then you won't see much that's simplified by 3d printing. Versatile robotic arms replacing specialized machines and automated guided vehicles as an alternative to conveyor belts are more helpful for small-scale factories, but those still don't solve the infrastructure requirements. The plastic insulation on wires in a car comes from a huge chemical plant, using catalysts made in another large plant. Float glass is made in giant factories. And so on. What's needed for the economy of a space colony is redesign of hundreds of manufacturing processes that each cost billions of dollars to develop.
maintenance & dust
Luna has very fine dust, which is a big problem for machines:
The dust environment is especially harsh on the Moon. Dust will coat mechanical components, causing abrasion of surfaces and wear of moving parts. The dust also forms a thermal insulator that makes heat removal difficult. The particles of the lunar regolith are very fine (< 70 microns, equivalent to silt on Earth), sharp, and highly abrasive. These particles will erode bearings, gears, and other mechanical mechanisms not properly sealed. The dust will also abrade seals. The lunar regolith contains at least 20 percent silicon, 40 percent oxygen, and 10 percent metals.
Lunar dust carries an electrostatic charge which enables it to cling to nongrounded conductive and nonconductive surfaces. Astronauts from manned landings reported that removing dust from their equipment was difficult. The accumulation of dust on optics and radiators is also of concern. Even small quantities on the front surfaces of refractive optics will severely increase stray light scattering.
If deposits for key resources are scarce, and resources need to be transported by trucks or conveyor belts between distant locations, rapid degradation of gears and bearings by abrasive dust could easily make the economy of a space colony unsustainable.
resource availability & locations
Civilization requires hydrogen, oxygen, carbon, nitrogen, metals, and energy. A space colony must be able to acquire all of those.
A floating colony over Venus at ~50km has been proposed.
The atmosphere of Venus has plenty of CO2 and N2, but only low levels of hydrogen. A Venus colony would require a large amount of equipment and energy to produce water from it, but it's theoretically possible. On the other hand, metals would be completely unavailable.
If significant amounts of water are present on Luna, that water would probably be buried ice mixed with lunar regolith, and only present in specific locations. That would need to be dug out, separated, and transported - which would obviously require a large amount of equipment per capita.
Mars has similar problems to Luna, and is farther from Earth. Yes, Mars technically has an atmosphere, but it's ~0.6% as dense as Earth's, so it helps with landing from space but provides no benefit over a vacuum for a colony.
How about asteroids? All necessary types of materials are available from different asteroid types, and transport of material is much easier in space than on a planet surface. The problem is that those different asteroid types are not very close to each other, and moving asteroids together would require a lot of impulse. Still, I think that asteroids are the best option for space colonization.
Rather than large rockets, I imagine resource transport between asteroids involving mainly spinning tethers.
Most asteroids are relatively far from the sun, reducing solar panel effectiveness. But space-based solar panels can be lightweight, and if concentrating light with reflectors then heating is a limiting factor.
Asteroids have negligible gravity, and sometimes gravity is good, but I think that rotating spaceship sections are an easier problem than dealing with dust and surface transportation of material on Mars. The material requirements for artificial gravity from rotation are proportional to diameter*gravity, so I'd expect reduced gravity and multiple cylinders of relatively small diameter.
Since nothing is completely rigid, a long rotating cylinder will eventually change its rotation axis. But active stabilization of rotation axis is not too difficult for smaller cylinders, and it's also possible to have collections of stable rotating geometries. For example, a large sphere of iron and glass that acts as a radiation shield and atmosphere containment, which contains a collection of spinning spheroids with holes in their ends. Perhaps with a lower pressure outside the spheroids than inside them. Of course, that would require pumping any lost air back into the spheroids, and continually countering atmospheric drag with motors, but perhaps that's worthwhile.
Why are big rockets needed for a mission to Mars? Why can't smaller rockets lift up parts of a spacecraft that are assembled in orbit?
The problem is, doing things in space is hard. During EVA repairs, tasks that would be simple on Earth took well-trained astronauts hours of hard work. That's because it's hard to do things in current spacesuits. Current robots aren't good enough either.
Well, sort of. Those are possible, but there are some serious problems. The much-publicized "MIT Bio-Suit" didn't quite have adequate pressure, and had gas-filled gloves which negates much of the point.
Only the arms and shoulders really need freedom of movement to do work in space. It's possible to make hard shells with elastic arm-gloves. But gloves are hard to do, because of all the joints and concavities of hands. Blood pools in low-pressure areas, but if you inflate joints with gas, then it's too hard to move them.
So, suppose you have some elastic gloves with spherical bubbles around all the joints. The force required to move those joints is too high for humans, but the stress-strain curve of each joint is consistent. That means the required force can be cancelled out using springs; it's possible to make springs with arbitrary stress-strain curves using rolled spring steel of variable width.
Then, of course, those bubbles would be inconvenient for manipulating things, but solid protrusions from the other parts of the glove to equalize the effective thickness would solve that problem.
It's also obviously possible to generate electricity at the same time: Take liquid hydrogen, pressurize it, heat it in heat exchanger 1, heat it with concentrated sunlight, expand it with a turbine, cool it with heat exchanger 1, compress it with a turbine, heat it with concentrated sunlight, expand it with a turbine, heat it with concentrated sunlight, and send it to a rocket nozzle.
While large mass drivers to launch spacecraft are completely impractical, linear motors launching small iron balls could be a viable means of propulsion for ships for a space colony near an iron asteroid.
Rotating arms could launch material from silicate asteroids at over 2 km/s with current materials. Because you don't want to apply too much force to the spacecraft when material is released, I imagine a counter-rotating pair of continuously rotating arms, with electric shuttle robots continually carrying small amounts of material to the ends for release.
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