Yes, if we had Single Stage to Orbit fully reusable rockets and if all issues involved in living on another world were understood, Zubrin's plan(s) would be a shoo-in. However, we can't even construct a reliable artificial biosphere fully enclosed here on Earth!
Learn to walk before you try to run. Let's work on sustained outposts on a world no more than three days' travel away first.
Certainly not essential to Zubrin's plan. There are modifications to Zubrin's plan that can be implemented with existing boosters, with on-orbit assembly limited to linking together 4 components. Seems doable to me.
However, we can't even construct a reliable artificial biosphere fully enclosed here on Earth!
Where do you get that from? For one thing, the most publicized efforts were tried by questionable people. I think a legitimate effort would account for things like curing concrete absorbing lots of oxygen. For another thing, there's a huge difference between a biosphere and air/water recycling combined with local agriculture. The point is not to get a 100% viable self-regulating biosphere. It's just to be able to use local resources. For initial colonization, it's just life support for plants. The 100% viable self-regulating biospheres will take decades to get right, but we'll have decades and lots of economic incentive once the colonization efforts are under way.
Learn to walk before you try to run. Let's work on sustained outposts on a world no more than three days' travel away first.
If the only thing to be gained from the moon is a stepping stone to Mars, then it's a waste of time. The environmental challenges are just about all different, so it's not even a good rehearsal. That's more like "Learn to swim before you run. Let's work on movement while partially buoyant, not subject to a full G, first."
I'm sure you could train babies to swim-crawl-walk. But if you want to walk, it's an unnecessary detour.
>However, we can't even construct a reliable artificial
>biosphere fully enclosed here on Earth!
Where do you get that from?
We just don't know how to live on other worlds. We are almost completely ignorant of the complexities involved in the process and have a whole bunch of unpleasant discoveries to make yet. That's not to say it _can't_ be done and that we don't know what should happen in theory, but we have never done it before. Ever. There is no experience to build upon.
If you want another flags and footprints mission to plant a candelabra of pennants on Mars and then scurry back after a few days of visiting, by all means piss away hundreds of billions of dollars and go to Mars direct for a quick visit. However, if you want to learn the actual skills required to live and work on other worlds, you should focus on building missions which demonstrate and refine the skills required to live and work on other worlds.
Doing so on our Moon and near-Earth asteroids (the nearest locations to support and safety) is the best way to do that and will give us the tools needed to move outwards permanently.
So, as soon as possible, start on agriculture. If you're going to prioritize that, then you need to prioritize the knowledge and skills for the most productive environment. If you had to settle North America from scratch, would you first try to figure out how to farm in North Ontario? No, you'd try to figure out how to farm in places like Virginia, for the toehold, then as quickly as possible move out to the midwest, where the really big yields are possible.
Mars is probably going to be the off-Earth agricultural power, like the American midwest. The Moon, with its lack of resources, including suitable forms of sunlight, is going to be like North Ontario.
Doing so on our Moon and near-Earth asteroids (the nearest locations to support and safety) is the best way to do that and will give us the tools needed to move outwards permanently.
Near-Earth asteroids are a good rehearsal for expeditions to Mars. Any techniques useful to Mars that we might learn from the Moon, we would also learn from Near-Earth asteroid exploration. I am all for this. They will also yield information relevant to preventing asteroid collisions. I say we save the Moon for when we have a use for He3.
However, we can't even construct a reliable artificial biosphere fully enclosed here on Earth!...no one has done it yet. Ever.
I don't think you need a reliable artificial biosphere to get started. All you really need is life support for growing plants. I'm sure there's some grow houses out there in extreme northern latitudes that qualify as exactly this. If you can reduce the weight of supplies by a factor of 10 or 20, then this is enough.
The ISS is also self-contained.