Here's an experiment which could be started relatively inexpensively, but which would yield significant results: Start with just recycling water. Build a simila

Here's an experiment which could be started relatively inexpensively, but which would yield significant results: Start with just recycling water. Build a similar facility, or build a new one, but at first, just try to completely recycle the water. This could be done through greenhouses completely enclosing an artificial wetlands, which would be used to recycle human wastes. Pure water could be recovered by running dehumidifiers. Such a facility could be built in the desert, much smaller, but incorporating the lessons of Biosphere 2. (For example, that conventional glass blocks too much sunlight, and that curing concrete releases CO2.) Next, just completely recycle the air. Only after that, see if the ecosystem could be expanded and food grown for the inhabitants. That should also be staged, with the 1st part involving just supplying enough calories, the next parts working towards complete nutrition. Instead of sealing the system from the get-go, first build it "leaky," then prevent the leaks.