Jon Goff relatively recently (over 2 weeks ago?) posted an interesting article
listing the various technologies required to make a civilisation spacefaring. I was going to comment on it last week, but I got distracted, and then after that I was on vacation last week at Jeju Island
Basically if the technologies listed were developed, it would allow relatively easy transport between the Earth and many locations in the Solar System. In effect, it is the makings of an interplanetary highway system. I love it!
But after reading his article and the subsequent responses and additions I still felt that there was something missing. But then I realized that his proposal is in fact quite comprehensive for what it is intended for - interplanetary travel. But this is only one side of the coin.
Jon Goff starts with a criteria that inteplanetary travel should be able to support at least the population of Tehachapi in order for the operators to qualify as truly spacefaring. I had to use wiki to find out that the population of Tehachapi is about 30,000
including surrounding areas. That's a pretty sizeable population to keep fed and pressurized.
Clearly the inhabitants of such a settlement would not, for the most part, be trading off the cheap real estate against the longer commute to Earth. Telecommuting is probably not a good idea either. The bandwidth might be ok, but the ping times to the company server would be dreadful. No, most of their work will be providing goods and services to one-another.
However the system won't be entirely closed. In order for such a population to thrive, there needs to be something they can barter for necessary supplies. Unless some kind of government subsidies are available for the goods being supplied (in which case is the country providing the subsidies really spacefaring?), the value of the exports should at least match the cost of the supplies, including transportation costs (Some government subsidies for the transportation infrastructure Jon described may be possible given that it will likely also be used by government space agencies and, possibly, military vehicles). It's unlikely, in my opinion, that mining, even rare earth elements, would be worthwhile at first. The exports with the most value for money would be services rather than goods and hardware. I could easily envisage such a community providing valuable scientific research, as well as other privately funded services such as virtual tourism. However would these kind of exports be of sufficient value to supply all the spacesuits, regolith moving equipment, housing components, etc that the settlers will need? I don't think so - in which case the settlers will have to be largely self sufficient, even while gradually expanding the size of the settlement.
Jon touched on this in mentioning ISRU and closing the water cycle, however what the settlers will also clearly need is a set of tools to allow them to be independent with the exception of small, hard to manufacture items. One key item is something that allows them to build custom structures from the available regolith. Think 19th century settler building a log cabin. They may also need to manufacture their own spacesuits, which may be quite crudely made at first and/or robotic equipment, and will require food production (farming) equipment, not to mention furniture, plumbing and other items to make the settlement reasonably liveable.
For a population to reach 30,000 in a space settlement, they would probably already have to have all the above capability, therefore these technologies would be required not just to maintain the settlement at that population, but to enable it to grow to 30,000 people in the first place.
What this all implies is that we really need to start putting some serious effort into developing the technologies to allow the maximum possible level of self sufficiency in a space settlement. In fact I would like to propose that until this technology is within reach there just isn't sufficient motivation to lower launch and space transportation costs to a reasonable level simply because until then there will be no feasible permanent 'there' to travel to. Robert Bigelow's space habitat is a fantastic start, but even so it won't allow anywhere near the level of independence necessary to start a colony, and without a nearby source of raw materials it won't be possible for residents to expand it significantly.
Note that I haven't been specific about whether the settlement is on the Moon, Mars, or a minor (dwarf?) planet or anywhere else in the Solar System. I really don't want to get into that debate.
One idea to get things moving is to offer (yet) another prize to be awarded to the first team to double the population capacity of a simulated settlement from 5 to 10 people over the period of one year with additional supplies limited to less than, say, 500kg. Initially a team of 5 would start with, say, 2 tons of equipment, which they could design themselves prior to starting the attempt, and would have to include an airtight habitat, pressure suits and oxygen. To make it more realistic, they could be provided with additional electrical power, in exchange for any solar cells they include in their initial equipment set, or manufacture on the spot. They would also be provided with an unlimited supply of simulated regolith.
I've no idea how much should be offered as the prize, but it would have to be substantial. If the above seems impossible now, even with some reasonable adjustment of the allowed equipment weight, it just proves how little effort has been put into making space settlement feasible and how much work remains to be done.
Another thought is that this kind of work could easily be undertaken by a space agency other than NASA. It won't require billion dollar investment, and there is plenty of potential for valuable technology spinoffs. Later on there will be recognition that this work is just as important as developing better boosters. I wish a country such as Australia (I am Australian, of course ;-) ), with significant in house mining and ore processing capability, as well as a can-do innovative spirit would get behind such a project. The benefits would be out of all proportion to the investment.