I don't like the way PHS has Scum Fleets as of right now. Not gritty enough for me so here's my take on them.
Scum fleets are more like the Quarian fleet from Mass Effect.
The whole fleet is this massive, amorphous blob of ships that is constantly strewn from one end of the solar system to the next. Though large, fairly unregulated, and mysterious the fleet is not the haven for gene hacking and augmentation that it is given to be. It is more a smuggling and crime haven that provides either of the two major factions in my game, the Jovian Republic and the Planetary Consortium a de facto neutral ground for certain clandestine activities.
Most of the ships are run-down, over-crowded, and radically converted making the scene more like a wandering bazaar of ever changing form and function as ships go from the rim to the core and back again but not the wildly active bio-modification bazaar pictured in the book.
Ships and scum are constantly competing for scarce resources and offering bootleg services to the highest bidder, most of the population are flats just looking for a place to stay. A few of the ships are massive databases that house additional millions of egos in cold storage. Passage through the fleets from the rim to the core or vice-versa is what brings in most of the income to the fleet which is governed by a loose organization of ship captains and lobbyist parties that attempt to look after the welfare of the Scum community. Passage is generally slow but most ships are comfortable with shuttles moving from the smaller skiffs to larger capital class and freight vessels quite often.
The primary quality of the Scum Fleet is the diverse environment and the complete lack of central police force. As such there is literally a lack of sousveillance and a struggling surveillance program to monitor at least general traffic through the fleet. This presents excellent emigration techniques and opportunities for criminal and clandestine trading.
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"And yet, across the gulf of space, minds immeasurably superior to ours regarded this Earth with envious eyes. And slowly, and surely, they drew their plans against us."