This entry is an informal response of sorts to a blog written by Charles Stross, which you can find HERE. Not that I think he'll read this, but I thought this might be something people reading the OV blog here might find interesting. I also touched upon this subject in one of the first articles I did for OV, Generations Ships.
In the original article, Stross postulates the difficulty in designing a society that could be stable enough to last through the centuries or millennia of the voyage. I think he was approaching the problem from the wrong angle.
You simply can't build a completely stable human society. Human history has proven that any institution established either mutates profoundly, dies off, or is absorbed by a newer one as the decades and centuries slip by. Human societies cannot be stable for long periods of time, its just not in our nature. Human culture is ultimately dynamic, not static, and that seems to be built right into our base psychology, if not our DNA.
Rather, you have to assume the human society on a generation ship is going to go through numerous upheavals and changes throughout its voyage. Its an inevitability. In fact, I'd even go so far to say that IT DOES NOT MATTER WHAT THE ORIGINATING GOVERNMENT OR SOCIETY IS. Its not going to last in recognizable form for more than a small fraction of any truly long-term voyage.
Realistically, the originating society on a gen ship will just be the builder society in microcosm. If the US built one tomorrow, the society would be the current US society in miniature. If China built one, it would be a mini-China, and so on. Its what the people starting the voyage would be most comfortable with, and imposing something radically different would lead to potentially a lot of trouble early on.
In fact, it seems an exercise in hubris by the designers, in assuming the generation ship crew will somehow be too stupid or inflexible to handle their own affairs, to the point that the builders have to impose excessively rigid societal restraints. It is true that a series of poor political decisions could have potentially disastrous effects on the environment or operation of the ship, but the same can be said of just about any government and its environs on Earth as well. Rather, we're just going to have to assume that the crew will adapt and grow to their environment on board in their own way, as our own societies have adapted and grown in unique ways to the world around us.
Instead of trying to impose rigid societal restraints that will just break down anyway, you need to provide the evolving society with one or more safety valves that will allow them to resolve conflicts with minimal threat to the ship as a whole. I think one of the most valuable of these would be living space.
Given the technology level needed to build a gen ship (which I estimate may come online at least 50 years from now, or at Tech Level 13 on the OV scale) how many crew do you really need to maintain it, given future advances in automata and AI? Probably not that many. So you leave most of the habitable space in your gen ship uninhabited; start with a small population, just big enough to ensure healthy genetic diversity, say a few hundred to a thousand. Concentrate them in one small town, and leave the rest of the habitat fallow. Depending on the size and design of the generations ship(Stross quotes an O'Neill-style hollowed asteroid design; it could also have many different levels or separate habitats), that could be from a few to maybe hundreds of square kilometers.
Over the course of the voyage, the crew will expand and 'colonize' the rest of the ship, giving them an added endeavor they can concentrate their energy on. Plus, when schisms and conflicts inevitably arise, the bereaved section of the society can just leave for 'new lands' elsewhere in the ship, giving them a hopefully better alternative to outright conflict.
The amount of fallow space you need to help mitigate potential conflicts would depend on a lot of variables, such as the size and design of the ship, the length of the voyage, and the size of the seed population. If planned out properly, the ship will reach its destination before all the internal space is used up. I do think this approach is the best way for a crew to mitigate the pitfalls of the inevitable ebb and flow of human societies on board a generation ship over the centuries.