[AlexanderHowl]

A lot of them were probably using the assumption of TL7 space colonization, so TL9 by 2200 AD might not have seemed all that unreasonable. With sufficient investment, you can reach Mars with TL7 technology (we did it in real life), it just takes a really long time. The point still stands that bigger is almost always better when it comes to manned spaceships, as larger spaceships provide more radiation shielding and higher spin gravity.

By TL9, fusion rockets allow people to go anywhere in the Sol System without Hohmann transfers, which cut transportation times greatly. In the case of going to Saturn, it quarters the time required. If you are going to Uranus or Neptune, it cuts the time even more, as the Hohmann transfers take 21 years for Uranus and 42 years for Neptune (contemporary probes do not use Hohmann transfers for such missions, as the technology just does not have the lifespan). Of course, in situ resource utilization is a requirement, as is total life support, as the missions are otherwise too long for humans.

If you wanted a Neptune colony mission, the costs would probably be $400,000 per ton of cargo, since the ship will likely not return soon enough for a route to be economical. Now, you could have the colony give the crew the spaceship in lieu of salaries, in which the crew probably transforms it into a clan ship. If there was a major puah, with one such ship produced every year for a century, you could have a hundred clan ships traveling through the Sol System, going from Earth to Neptune every fourteen years. As long as the clans make enough to survive, I doubt that will care much about the economic viability of the model.

Similar clans could work the Earth-Main Belt, Earth-Jupiter Trojan, Earth-Saturn, and Earth-Uranus routes (Earth-Mars is too close for such spaceships to remain independent). After a century, every clan ship would have its own customs and traditions, though they would likely marry outsiders to prevent inbreeding.