Tian

A binary star system, Tian is a main sequence star that the rest of the system orbits, with a red dwarf named Pheonix orbitting at the very edge of the system. It is theorized that Pheonix was a rogue star that became caught in the gravity of Tian while passing by, and has been trapped ever since.

Capital

One of the colonies founded during the Great Expansion. Originally slated for traditional terraforming, early setbacks prompted the bluntly named Capital Arcology to pivot to a new direction. Capital decided to focus its tremendous resources on expanding its industry and manufacturing power rather than on terrforming, producing benefits and results within a single lifetime rather than aiming for goals hundreds of years out. As a result, Capital to this day has had almost no actual terraforming take place beyond basic safety essentials like the construction of the Capital Webb station. However, Capital is an economic powerhouse in the colonies. It produces products and parts for virtually everything and sells them to virtually everyone. While established planets like Rhineland may be able to have thriving local economies and industries, most stations and arcology worlds depend on Capital to make what they cannot. Every supply line runs through Capital factories evntually.
Militarily, Capital technically has the largest Spacy by number. But this is misleading. Capital warships are produced cheaply, and while it has a lot of them they do not match up well one on one with the warships of other planet-nations. Of course, that was never their intended purpose. Capital Warships are designed to be cost effective in bulk, simple to repir, and affordable enough to sell to smaller nationstates like space stations for their defense.
Capital is ruled by a psuedomonarchy known as the First Family, made of the descendants of the command staff of the original colony mission to Tian. The narrative is that the First Family was chosen to lead from the start, the best of the best that Earth could offer, and thus is inherently better suited to lead. They use the continued success of Capital as proof of their right to rule. Technically, they consider themselves a meritocracy, and thus while rare it is possible for someone of lower class to earn their way into First Family membership. The First Family, as the owners of Capital and its immense economy, are extremely wealthy. They also place great stock on making sure that the First Family is raised with the best education possible, and most members of the First Family are indoctinated from a young age to believe that they really do have a responsibility to be the best of the best, for the good of Capital.
The rest of Capital is taught that they too have responsbilities to work for the benefit of the nation. Not all of them take to it willingly. There is a musical subculture that has spread to other worlds known as Capital Drill which can best be surmised as 'space punk', which is distinctly anti-authority in sentiment, and anti-first family specifically. While famous across human space, Capital Drill is technically illegal in Tian and producing or selling it can be considered a form of treasonous activity, should the authorities choose to prosecute it as such.
As the largest economy in the colonies, Capital's physical money (the Petal, a shaving of proprietary Lilywood encased in a bead of platinum) is the defacto currency of interstellar trade. Technically the UCH puts out the Chit in what is supposed to be a standardized currency to fill the same role, but the Petal is much stronger and is what people actually use, even if Chits are still accepted almost anywhere.

Notable Stations:

Mons Gemini
In orbit of the red dwarf star Pheonix, on the edge of Tian system.
Like all stations that bear the Mons prefix, Mons Gemini is embedded into a prexisting stellar body rather than built from scratch. Mons Gemini itself is technicaly two such stellar bodies, the two peices of a large chrondite asteroid that split during mining, now joined by a manmade hub. What the locals call Little Rock is a rotating 11-mile wide chunk of stone that contains the spaceport and trade hub, and the Big Rock is a 97 mile wide asteroid that houses a large industrial sector devoted to refining, smelting, and processing the bounties of asteroid mining ventures. Most of Big Rock is actually left undeveloped and uninhabited, a natural shield kept facing Pheonix to block the star's radiation and occasional flares. Unlike Little Rock, Big Rock has no spin and is thus left in a state of zero gravity.
The proximity to Pheonix makes Mons Gemini an important transit hub for the Tian system, resources can be launched towards Pheonix and pulled in by the star's gravity before being intercepted by Mons Gemini's collection crews, and the star itself can be used for a gravitational slingshot to launch the refined materials anywhere in the system they need to be at a fraction of the usual propellant.