This post started as a response to a thread on Reddit. But my answer ended up being too long to actually POST to reddit.

It sounds like you've spent more time developing your ships than your setting. Which is a fine start, but you are going to need to do better. Audiences don't get excited by plumbing and propulsions systems. (And those that do are going to insist that they are realistic.) People get excited by people. Ships are literally just a means to an end.

My intention is to help, so as you read my feedback I am not pooping on your ideas. Worldbuilding is hard. Nobody gets is right. Just some of us manage to produce something plausible. (And I'm not even published yet, so take everything I'm saying with an extra grain of salt.)

I have been working on a concept for a world that basically justifies the existance of a hero ship I came up a little before the pandemic. "The Arther Charles Clarke", but for everyone on board it it simply "home." A Generation ship that is halfway on its way to a sun-like star 48 light years from Earth in the constellation of Scorpius. But for all of the cool rotating decks, and fusion powered farms, something always nagged me: who on Earth would pay the exorbinant sums of money to build this thing? Especially because it had no way of returning back to Sol.

And that got me to thinking about the cold war, and how programs like Apollo were funded. Basically as a way of having a proxy war because fighting an open war would be far too costly. And also like Apollo my "Project Iliad" was basically built on the backbone of a doomsday weapon.

It was then that I decided that to develop my factions on board the ship, I had to understand the world that built the ship. And I shifted focus to the Solar System a century before the ship was launched.

My feedback is based on my experience world building this Solar System.

Now you have a lot of infrastructure that, frankly, is in the wrong places. At least according to the calculations I've done for a world with a similar set of restrictions, that is also based on implosion fusion cells. At least for vessels under a certain size, and operating within a certain range. For long range vessels, they use heavy water catalyzed by anti-matter. Because it's really hard to find lithium deposits in the outer solar system.

First off, despite what Babylon 5, the Expanse, and Elon musk may have led you to believe, Mars is never going to have much more than a research colony on it. You pay a lot of gravity tax to access basically the same resources that are available in the asteroid belt. The moons are not that large, and their orbit is not that stable. The climate isn't suitable for life. Heck, the planet doesn't even get enough sunlight to power a decent sized colony.

The kindest thing that can be said about Mars is that it cleared its part of the solar system. You wouldn't need a "skyhook" to propel things out to Neptune if you just built the things in orbit.

Second: with billions of people Earth is never going to be one government. Even if all of the governments are under one umbrella, you are going to have vast differences in how various regions are governed owing to climate, resource distribution, and local culture. And P.S. local culture is constantly evolving. There is also going to be in-flghting (and occasional open war) between regions, even under one government. Just look at the United States, the former Soviet Union, and even China for that matter. The most effective Empires are actually de-centralized with distributed control. Totalitarian states rarely outlive their founder, because central control is actually really inefficient. It is wonderful for enriching the livestyle of a few elites (looking at the Nazis and the Soviets and the Communist Chinese), but it leads to terrible outcomes for the people. People will only starve for but so long before they rebel.

So what you get is a cycle over decades where totalitarian states rise to power, and violently fall apart. On the margins people realize that it's better to simply govern themselves. Over time those chunks are not re-conquered when the next empire is formed. And that's how you end up with basically Europe. Yes, NATO and the European Union exist. But there is little that is keeping one country in NATO or the EU from doing whatever it wants in another part of the world. (I'm looking at France.)

Different regional-come-global powers will dominate the development of the Solar System over time. And each will probably have a different set of priorities. Which adds flavor to your world. Certain outposts have Chinese names because in the late 21st century they had colonies to collect resource X. They are inhabited, today, by English speaking people with Australian accents because in the 22nd century their power base collapsed following the great Pacific war, and Australia drank their milkshake. (This is strictly a hypothetical for all of my Aussie and Chinese friends. Feel free to replace this with your own head cannon.)

In my world Psyche was established by the Japanese, backed with money from Irish money laundering... er Banking institutions. Psyche ended up becoming the capital of a faction known a ISTO, but the Japanese are kind of known for being a bit... territorial. As a result, Japan still owns the actual planet of Psyche. And the ISTO leases a set of tethered space stations above Psyche. But nobody from "outside" of the cult who performs the actual mining on Psyche is permitted on the planet.

One tip I would recommend is actually wargame out your future reality. If you want to start off with the world as it is today, start it out like the world today. And then play out the world as a series of agents (in your head) responding to random occurrences:

  1. Major technical innovation
  2. Wars
  3. Disasters
  4. Market booms and crashes
  5. Revolutions

You are going to have to basically write a little history book. No more than a paragraph or two for each event. As you fill out your timeline, expand your map.

In my world, I actually started in 1777 and developed an alternate history. I also have a mechanic in the magic system that allows for multiple universes, with any attempt to violate causality simply jumping from one universe to another. Try to time travel? Well you end up in a past of future that is completely different. Faster than light travel? Well you might arrive at your destination. But in a universe where humans never evolved in the first place. And thus I sprinkle my fictional world with contact to our world through famous people that disappeared.

The Alternate history is basically to Clarke-proof my stories. 2001 was fascinating when read in the 1980s. Trying to read it today ... well ... the story didn't age well. But if you, say, decided that your world is one in which George Washington was shot by a sniper, and the entire American Revolution worked out differently... audiences can buy that up. (Look at the success of "The Man in the High Castle" and "For all Mankind")

And, lets say, they developed nuclear power before the automobile. And had atomic rockets by the time we had the first world war? Oh my... what if their first world war had nuclear weapons? You can repurpose historical figures to help your audiences connect with your world. But then, because everything is a little different, you have a free hand to develop the world in a way that supports the setting for your actual story.

For mine, I also wanted to justify a sci-fi world populated with D&D magic users. Part of my alternate history is the occult having far more sway on the development of science. And a medieval alchemist surviving the French Revolution who didn't in our world. (And of course, how a medieval alchemist was still alive in the 18th century, I leave as an exercise to the reader.)