Tannhäuser Gate

Tannhäuser Gate is a space station located in the Solar system. It is located at the entry point to the Sol-Centauri starlane, the only lane departing from the Solar system. With a permanent population of over 280 million, it is by far the most populated artificial object in the galaxy. 
 
Initially a deep space military-scientific station, it grew substantially following the colonisation of Alpha Centauri. It developed as a major mining and trade hub, as well as a resupply station for ships arriving from and departing for Alpha Centauri. The station kept growing until it eclipsed the military installations located in its vicinity. 
In 2277 the Federal government ceded the station to the newly-created Tannhäuser Gate Corporation which became the local civilian government. The Tannhäuser Corporation has ensured the station retained high levels of autonomy due to its particular status. Citizens of the station are usually exempt from certain federal taxes and obligations. The TGC is one of the rare non-commonwealth administrative units of the Federation to be represented in the advisory Host of Representatives. 
The station's population was initially overwhelmingly constituted of miners from the outer Solar system. Over time however, as the station grew richer from trade, it began attracting wealthier citizens. Today the station's citizenry is made up of descendants of the original space workers and upper middle-class Terran citizens which moved in within the past few centuries to enjoy some of the advantages of the local legislation. The alien population has steadily climbed, reaching 18% in 2723. Aliens have largely replaced human space miners.