If you think robots should do everything then you might as well retire the human race. Why even bother to live. Why explore the stars when you can get a robot to do it for you?
If the goal is "put man on Mars" then that's what you gotta do. It's harder to make the argument that you need to do that in the service of science, or even offworld colonies, given the unsuitability and impracticality of those both.
Colonies on Mars are what drove the founding of SpaceX. Elon was looking up NASA's plans about sending humans to Mars and found that they simply didn't exist. He wanted to send a greenhouse to Mars while streaming its growth to get people inspired and thinking big again. NASA wasn't interested, Russia wanted too much $$$, so SpaceX was born. A colony doesn't mean you live there forever - it simply means a permanent human establishment. Some people will want to go back to Earth, some will want to stay on Mars indefinitely.
This is a big part of their obsession with lowering costs to space. When the launch costs are not such a huge economic factor, you have much greater leverage with doing things like building, resupplying, or even engaging in interplanetary commerce.
His main motivation was about making humanity a multiplanetary species, largely as a means of ensuring humanity's continuation. It sounds hyperbolic, but Earth has gone through multiple mass extinction events and we're rather overdue for another. And while those mass extinction events were all natural, there's also endless ways you can imagine us all managing to kill ourselves off. And, critically, all of these hyperbolic scenarios will seem extremely improbable up to the very day that one does inevitably happen. So the best time to start would be 50 years ago. But the second best time would be right now.
So the most logical place to start for this sort of 'humanity guarantee' would be Mars, which shares an oddly large amount in common with Earth. There's a verbose (and rather entertaining read) with lots of first party commentary here. [1]
This has been covered before but saying that Mars would be a “humanity guarantee” is actually extremely illogical, not the most logical. Short of the Earth getting blasted to tiny pieces in some way there is no scenario where Mars is more habitable than Earth. This is the sort of sci-fi Utopianism that this sober article is standing in opposition to. Mars may be the second most habitable place in the solar system and it’s infinitely less habitable than a nuked-out fallout-ridden earth or an overheated green house earth. There is no magic scenario where Mars suddenly ends up with a magnetosphere and an atmosphere.
Mars not having a magnetosphere isn't as short term a need. The atmosphere stripping away is on geologic timescales, not human ones. Even then, we could put a superconducting ring between Sol and Mars and get the same effect as far as solar wind stripping the atmosphere. It would be a big project, but not impossible. It's also a project that won't possibly start until people live there permanently.
Worrying about the atmosphere stripping away is akin to worrying about the smaller of Mars two moons being on a path that will impact in 100,000+ years with the surface of mars.
In many problem domains mars is an easier target for long term habitation than the moon, the biggest challenge is getting there. The retorts from people here about farming miss that we don't need 'soil' to farm, there are techniques that mostly just need water and vitamins that can dissolve into it. At Epcot they have a system to breed fish and use the fish waste for feeding plants to grow. Throw in mycelium for handling human waste and you have an efficient system for augmenting food production.
A serious effort for mars will have as many or more spinoff technologies as Apollo gave us. The computers we are using today are further along in development from the massive influx of effort to make computers that could fit in space capsules. With the acidification we are causing in the ocean, a reliable way of converting C02 to oxygen at scale might be needed here on earth to prevent an oxygen collapse within decades. Climate change is a bitch, and it could give an excuse to start charging people for breathable air here on earth so the cynics may be right about that eventually happening. That possible disaster just isn't on even most climate scientist radars yet.
There will be other spinoff technologies we just don't see yet. The large rocketry needed to get there also opens up resource extraction from near earth objects. There's massive material wealth just barely outside our present grasp. It would be nice for materials like platinum and gold to follow in the footsteps of aluminum in becoming common enough to be usable for trivial items. Aluminum was a precious metal just a few hundred years ago in its refined form. Gold nanoparticles look like a candidate that could make current GLP-1 drugs obsolete, it works in animal studies but not tested in humans yet. Manufacturing in space is also on the verge of practicality. Metal foams, ultra low attenuation glass and optically transparent aerogels can be made in microgravity that are superior to the versions that can be made here on earth. Metal foams would be ideal for making ships, cars and planes that are much lower weight than we can make now without loss of strength, less weight means fewer watts per mile and less material needed.
The people whining about the idea always seem to miss the secondary effects of making the effort and always see to paint the optimistic take as naive, really they are just demonstrating short sighted thinking.
This logic does not necessitate Mars ever being more habitable than Earth. Imagine one of the countless doomsday scenarios - a large asteroid impact. What kills you is not necessarily the asteroid, but it flinging debris into the sky that blots out the sun, not only creating a massive cold, but also rapidly killing all plants which starts a rapid series of extinction events on up the food chain.
If that happened Earth itself would still, even during the extinction event, be a dramatically more pleasant place than Mars. But nonetheless that event would kill off the overwhelming majority of people on Earth, and very possibly 100%, because it's such a significant change from the status quo we expect to continue on Earth. But having a parallel society or societies would ensure that even in the 100% scenario, life could get back up and organized relatively quickly. And even in the "only" 99% of people killed scenario, the outside help could help to reestablish order and kickstart society.
You could build a better 'colony' on earth to survive that event for way less money/effort/risk than a colony on mars. You aren't going to have a colony on Mars contributing back to the home planet in any meaningful way, and 1% of people left on Earth is still 80,000,000, many more than will be in a Mars colony.
> You could build a better 'colony' on earth to survive that event for way less money/effort/risk than a colony on mars.
How though? Not in terms of engineering, but in terms of politics and economics. The biggest charter city in the world just got ruled illegal and Honduras is about to take their stuff. Building colonies in Antarctica is forbidden by treaty. And much like Thoreau's cabin in the woods, if you try to make a self-sufficient colony somewhere that's not actually isolated, you might think you've succeeded but actually have been cheating all along.
Yes, objectively there are better options, just as e.g. ITER could have been built a lot more efficiently if most of the countries had agreed to pay one country to make it, instead of making precision parts in a bunch of different countries and having to assemble them together. But engineering and politics are the art of the possible.
Building colonies in-planet that could survive all possible scenarios would probably be impossible. But even if it were you'd face a pretty simple problem - who would ever want to live for there? You'd likely end up living in conditions that would make life on Mars look pleasant, without any of the upsides that might take people to Mars - adventure, ideology, commercial aspirations, perhaps even religious (you know the Mormons will want a planet or two), and of course 0.3g!
And who knows what the future holds in terms of population sizes? I also strongly disagree on the colonies not being able to engage in exchange. For a silly but very practical example sports in 0.3g are going to be insane. Jordan could jump something like 11ft and stay airborn for several seconds on Mars. That's going to be just be stupidly awesome to watch and play. MMA will look like a something out of a Chinese martial arts movie. For more mundane things, as the price of shipping cargo decreases the number of things available for trade increases. For example wine made in 0.3g will taste very different. Whether that's better or worse is yet to be discovered, but obviously such ideas will have no difficulty finding a market.
For better or for worse Mars (or the Moon) will also probably make amazing retirement places, especially if we can work on the scenery a bit. Taking that load of old bones might not only provide comfort but even increase longevity enabling a weaker heart to keep pumping a bit longer. And so on endlessly.
For me first logical step is to ignore the getting there part. And prove that we can actually build colony here. In suitable location say for example Sahara or Antarctica. After those technological challenges are solved next step is to see how to get it to orbit or make same in orbit. And then we can start thinking how to get all the stuff over there.
There's not really a plausible path to colonies on other planets (or on moons of Jupiter or Saturn) that needs to send humans there soon. Establishing such a colony and getting it working well enough to actually last would be a long term project, and it would be decades before it got to sending people.
Before that there would be a lot of work off Earth, including manned work, but it would be in space or on the Moon.
They key is Lagrange points. Each pair of bodies (Sun/Earth, Earth/Moon, Sun/Jupiter, etc) have 5 points where the gravitational forces from the two bodies balance out in a way that makes it possible for something to orbit that point, even though there is no massive body at that point.
Two of the Lagrange points are stable, meaning that if something in orbit around them is disturbed it still stays around that point. The other three are unstable. Disturbing something there will cause it to get farther and farther away.
You can use this to move things from Lagrange points of one pair (Sun/Earth for example) to Lagrange points of another pair (Sun/Jupiter say) very cheaply. Get it to the starting point, and then nudge it into an unstable orbit that will have it getting farther and farther away. We can calculate these unstable orbits well enough to pick one that at some point is nearly tangent to an orbit of the destination Lagrange point that moves toward that point rather than away. A little nudge them can move our ship into that latter orbit.
The catch is that this is slow. It might take decades or more to make the trip.
The way you would use this in a colonization program is to build a series of unmanned cargo ships. Say a new cargo ship is completed every year. It would be stuffed full of supplies the colony will need, send to an appropriate Sun/Earth Lagrange point, and nudged onto its journey.
Let's say these ships take 30 years to reach the destination. After we've been doing this for nearly 30 years then we'd send a ship with the colonists. That ship uses a fast but expensive orbit. It would only need to carry the colonists, the supplies they need during the trip, and fuel and supplies for an emergency return trip in case when they get there they find some reason that they cannot stay.
Note that it doesn't need to carry any material to actually build the colony, or food and water for the colony. All that is in the cargo ships that are now arriving yearly. (If we are sure that the cargo ships are making it the human transport ship could even omit food, water, and fuel for an emergency return. Those can be on the first cargo ship).
You'd want to build the cargo ships on the Moon, or build them in space using resources from the Moon, because getting from the Moon to Lagrange points takes a lot less energy than getting from the Moon to Lagrange points.
The most plausible path then is to greatly expand industrialization of the Moon and the space near Earth. Probably then expand that to include space bases at some of the Lagrange points.
Then it is time to start working on colonization.
Unfortunately we'd probably not do Mars this way. If I recall correctly the low energy Lagrange transfer orbits to Mars are particularly slow--over a thousand years if I remember correctly.
If you think robots should do everything then you might as well retire the human race. Why even bother to live. Why explore the stars when you can get a robot to do it for you?