Worlds of the System

    There are dozens of intelligent species in the System, but only a handful have a significant presence in interplanetary space. Producing spaceships requires the kind of highly-developed orbital heavy industry that few planets possess. 

    (Most) spaceships are moved by chemical rockets which operate by destabilizing metastable metallic hydrogen. This metallic hydrogen is harvested from suspended clouds of particulate in the atmospheres of Eos and Phaethon, two of the System's gas giants. The "mining" procedure is very safe, in modern times, and can be performed almost entirely by unmanned aerostats. Collecting the fuel is what's dangerous — piracy abounds, and an oxygen leak in the fuel-rich atmospheres of the gas giants will result in terrifying firestorms visible from orbit.

    Control over fuel production is control over the System. This has been conclusively demonstrated in the fifteen years since the end of the Second Battery War. At the beginning of the hostilities, Lith and her allies — the Sylvans of Satanazes, the mercenary armies of Koss, the theocrats of Pure and an engineering corps of callow Avian idealists — were opposed by fleets of pirates, rebels, adventurers, mafias, industrial magnates, technological adepts, factions in their own parliament, and the obscure influence of Phobos. The suggestion that fuel production might be entirely annexed and nationalized by one planet inspired strange alliances. Civil conflict erupted even on planets not officially engaged in the Battery War; Lith's brutality in seizing or destroying all foreign stores of fuel, even those in civilian hands, was matched only by their enemies' determination to recover it first. For a time, interplanetary trade was disrupted by the fact that no cargo could be as valuable as the engine that moved it. The capital of Lith was blockaded for two years and its space elevators were sabotaged. Holy sites across Pure were destroyed, some by orbital strikes, others by suicide attacks. Hundreds of stations throughout the System were bombarded by either or both sides. Millions were killed.
    But the Second Battery War could only ever have one outcome. Early supply issues led inexorably to later military catastrophes, and when Lith succeeded in monopolizing production, those who had opposed them found the gates of heaven closed and barred. Fuel is monitored now, and its disbursement tracked. Of course, some slips are still made, despite all of Lith's precautions — piracy abounds, after all, and a small-time operator may grow desperate enough to sell her scrip to a friend with dire need and deep pockets. But the era of the Free System is over. There are no fleets left to check Lith's ambitions. Opposition to the hegemony, where it exists, now takes subtler forms.

Sizes are illustrative; the planets are depicted ~two orders of magnitude larger as a visual aid.

Ava

    Ava is a gas dwarf with a rocky surface. Its atmosphere is dense, foggy and cold, but full of volatiles the Avians synthesized into the first rocket fuels. In prehistoric times the members of the Avian species fought for access to higher nests farther up the rocky mesas and pillars which make up the landscape, where their eggs would be protected from shuffling ground-based predators. It's a common evo-psych Just So Story that this behavior is what drove them ever higher, building homes and towers, and eventually ships to take them as high as anyone can go; interplanetary space.
    Avians follow a strict caste system. All Avians are hexapods; those whose third pair of appendages are feathered wings are Scholars, those with bat-like wings are Soldiers, and those with monstrous oversized hands are Servitors (nowadays called Workers due to a social-justice fad sweeping Ava). These traits don't breed true; Scholars have an equal chance of having children who are soldiers or workers. Because of this, Avians do not form biological family units. All Avians are raised by the state.
    Scholar-caste Avians are the largest and (according to the majority opinion of Avian scientists) the smartest. They occupy choice spots in the bureaucracy of Avian governments, and are the most visible caste off of their homeworld. They like to say they have the temperaments of "ambassadors" and "architects", but more accurately they are "meddlers" and "enablers"
    Soldier-caste Avians are the smallest, and since Avians are the smallest space-faring species this makes the soldiers very small indeed. They often serve as pilots of small craft and are by far the most numerous caste off of their homeworld.
    Worker-caste Avians are the strongest, though not as gifted at war or politics as the others. There are just as many workers as any other caste (or more, considering the mortality rates of fighter pilots) but since they rarely leave Ava you wouldn't guess.

Engineers

    On the topic of "meddlers" and "enablers": when Avians first invented interplanetary travel, they visited every world with a species that could talk and made a simple offer: give them half of the money on the planet, and they will build a space elevator. This led to the First Battery War almost immediately.
    But still, almost every captain in the System has at least one Avian officer. Their intuitive understanding of the dynamics of space travel and the mechanics of a ship's engine make them invaluable additions to a crew.

Purity

    Purity is a young and volcanically active terrestrial planet controlled by a theocratic world-government. There's a stark divide between the city-dwellers who submit to the theocracy (and by extension Lith), the wastelanders who are one step from being completely feral, and the space pirates who acknowledge no authority except their god and their guns. The Pure are a little insectile and a little reptilian, with high population variance in types-and-placement-of-limbs. Some have spider legs, some have additional arms, some have bat wings, some have clawed pedipalps.
    Their god, Pure, is the six-armed guardian of the Gates of Death and judge of mortal souls. In one hand he holds a toothy spear and in another a barbed lash, in a third the keys to Hell, in a fourth a lantern whose light reveals honest men, in a fifth the great and heavy book where your sins are recorded, and with a sixth he turns its pages of smoking brass. Fond of fighter-pilots and infantry. Hates snipers and landlords. Pilots of all species wear his symbols as lucky charms.

Lucky Charms

    Lith's state religion is the Communion of Measure, or the Compassers, depending on your translation. They have accepted and absorbed the gods of other worlds, though they renamed them after their planets in the process. The gods obviously favor Lith over their own people, and a wise businessman never misses an opportunity to capitalize on a positive relationship.
    Non-Lithians are not as eager to adopt the mores and tenets of other cultures. The one general exception to this rule is the god Pure. All spacers are afraid of "dying cold" — to run out of food, out of air, to be pinned under rubble or impaled on flotsam and die of thirst, to bleed out slowly, or (the unnameable terror) to float off into the dark with no tether, no radio, no jets, in a suit topped up with oxygen, and nothing at hand sharp enough to cut your tubes, or sturdy enough to break your faceplate. Superstitious spacers wear Pure's octagram and hope it guarantees them a hot death.

Satanazes

    Satanazes is an unmapped and untamed world. Woses, the males of the dominant species, are obligate carnivores, in that they are obligated to eat animals: when they see an animal, they eat it, even if that animal says "wait please I'm an ambassador I just want to talk please aah". The only creatures that Woses don't immediately reflexively attack are the Sylvans, the females of their species. When circumstances demand that they communicate with others, they do so through the intermediary of their many wives. When circumstances demand that they communicate in person, they show up wearing Scary Attack Dog gear with sturdy chains their wives hold like zeppelin anchors (picture a conversation with a bus-sized tiger that tries to jump on you every few words, held back by half a dozen catgirls). Lithians occasionally try to Weyland-Yutani an adolescent for scientific study, an endeavor with a 100% catastrophe rate.
    As for the Sylvans, at birth there are roughly three of them for every Wose, but as the males grow to adulthood, establish territories, and fight each other for status that ratio increases to more than 10:1. The Woses simply can't keep up with the demand, and so many Sylvans seek both employment and romance off-planet. Many Lithians have problematic attitudes about them.

Painted Tongue

    The Sylvans have a complex tradition of body modification and decoration, which in these days of interplanetary travel has both spread to and been influenced by the other worlds of the System. Piercings, especially facial piercings, are unsuited for spacesuits and breathing tubes, so many Sylvans have brightly-colored but meaningless tattoos splitting their lips or brows, or across the alars of their nose. They think little of clipping their own ears to better fit their helmets — Sylvans heal rapidly, even from serious disfigurements.
    Those who wish to be genuinely outre (which is most Sylvans) must go to more drastic lengths: false teeth of gold or surgical steel or black ceramic, auxiliary lenses, needles of magnetized neodyme in the fingertips, carbon filament knitting sheathing the ribs. A symbolically important modification, rarely imitated by other species, is what Sylvans call umineko: to gnaw off the tip of one's own trigger finger, declawing it, and making it possible for them to handle guns designed for other species.

Koss

    The Koss homeworld is a freezing ocean planet. They were a happy, peaceful people once; tubby walrus-frogs well-suited for their place in the ecosystem, content to swim and sing and live off of kelp and anchovies for a million years more. When the Lithians noticed how big and brawny they were, and beamed them up, and taught them how to make war, the Koss discovered that they were good at fighting. They enjoy it so much that the majority of Koss adults off-world are employed as shock troopers and policewomen to this day.

Contracts

    One half of a Koss contract slightly resembles a vacuum tube, though the low-density nacreous boron ceramic (LNB) shell is much more durable than glass or wire. Mated, the two halves reveal fine-detail legalisms, which typically begin with the religious formula "It appears that she who bears the one part of me owes five years" (or whatever length) "of armed service to whosoever bears my other part, howsoever it be obtained". The Koss regard these trinkets with fatal seriousness. Treasure-troves of legend often include the "rash boon", a contract of indefinite length promising the bearer arbitrary service from a hero, though this practice is not historically attested. 

Lith

    Lith is a desert planet very close to a powerful star. The biosphere is limited, and irritable. Lithians themselves are horned and bat-faced humanoids with long gangly arms and stubby powerful legs. Their skin is slightly-luminescent lavender in the visual range, and mirror-bright in higher EM bands. None of this is important information; what matters is that they won the Second Battery War, and the System is theirs.

Megastructures

    Lith's enormous industrial capacity is sometimes tapped to support grand Parliamentary hazards. Some are moderately successful, though rarely to the degree promised, and never enough to justify the enormous cost in blood, treasure, and the time of engineers.

• Emitter Bloc
      A swarm of power-collecting nodes orbits the sun closely; each of these sends a beam of directed energy up to the swarm of control nodes which orbit the sun at a distance; these in turn direct powerful masers and lasers towards innumerable reflectors, retransmitters, beam expanders, radio arrays, and both manned and unmanned deepwater installations. The Lithians use the Bloc to secure and obscure communication. Recently (or not so recently — secret projects are hard for outsiders to keep track of) they have even begun using it as a form of propulsion for stealth probes, which can be precisely maneuvered by limited bursts of energy caught in retractable sails. If you had the correct access codes, and a compatible sail, you could use this system to travel anywhere in the System you wanted, at impossible speeds, using no fuel, while remaining no more conspicuous than any piece of lifeless space-junk.
      The notion that the Bloc could be used to destroy a planet is, of course, absurd. The energy requirements, the wear and tear on components, the fact that the planet-destroying beam would have to be bounced off of a series of large mirrors — impossible. But you should still try to avoid driving your ship into one of those emissions.
  
• Mechanical Intelligence
      Sailors tell tall-tales of machine-minds going insane and turning against their masters. The engineers who build the devices know this is a fundamental misunderstanding. A "mechanical brain" is nothing like a brain; it has no volition and no agency. It is a clockwork device to calculate orbital trajectories, intersection ranges, and other matters which would be slow and imprecise for a (non-Avian) pilot to calculate by hand. It can only turn against its masters in the way of all machines: by failing, like a jammed gun or a leaking oxygen tube.
      Still, Parliament dreams of a machine-mind that can not only calculate but decide what must be calculated. Then the grim-faced Avian engineers would be made obsolete. Perhaps Lith would be able to exploit Ava's greatest secret: the Sewing Drive, which allowed Avian freedom-fighters of the Second Battery War to cross the System faster than the radio waves that warned of their approach.
      The engineers, for their part, have never provided such a machine.
• Company Loyalty
      The B.S.L. Hand That Feeds is a research vessel in orbit around one of Satanazes' dead moons. Two years ago they began experimenting with a new non-invasive transcranial magnetic procedure on their stock of Woses. Their first few attempts led only to aneurysms, partial lobotomies and fatal grand mals, but yesterday they had a breakthrough: if a certain portion of the amygdala can be targeted and electronically destroyed, the Wose loses its hostility to non-Sylvan life. There appear to be no other side-effects of the procedure.
      The lab crew are now split, evenly, on the question of what they should do with this knowledge. But how can there be an argument against applying it to the entire male population of Satanazes? The primary cause of mortality among Woses is death at the hands of another Wose. Surely, say one half of the team, this treatment is as ethically straightforward as a cure for cancer — or for suicidal impulses, if you prefer. There's no moral value to being brutally murdered by an apex predator, no matter how romanticized or "natural" your life might have been.
  

Phobos

    Phobans [or Phoebans, my notes disagree] come from Phobos [or Phoebe, ditto], a debris field orbiting the dead twin of the System's sun at an extraordinarily far distance. Their homeworld's star was stillborn, deprived of essential stellar material at birth and ripped apart in the formation of the System
    The Phobans are used to darkness, crushing gravity-shocks, and the near-silence of trace atmosphere. When they visit other worlds they wear protective, concealing garments, and speak very little through the medium of crackling radio.
    They have hated the Lithians since they met them. Phobos is the sole polity of the System which never officially agreed to the armistice which ended the First Battery War, though hostilities ended generations ago. It takes months or years to reach Phobos by rocket, and dozens of hours to contact it by radio.

Graffiti

    A spaceman who visits enough far-flung stations will see symbols repeated in unlikely places. Even in the high, high wilderness, out past Phaethon, you'll see the tags, badges and seals of the same distant gangs, regiments and academies painted on the walls or chipped into the paint.
    One motif is the "midnight sun", a yellow disc on a black field. For those who can put aside the victories and defeats, the profit and the loss, it symbolizes the freedom Lith promises: freedom from oppression, freedom from want, freedom of self-expression — nothing like the freedom of the Free System. It might appear in a rewinding station to mark the speakeasies of the counter-revolutionaries, or on a mining base to show the way to a supply cache, or it might be found on a distant asteroid, a hundred million miles from Lith, over a mass grave.
    For their part, the Phobans hate the symbol (and for this reason it's sometimes used as nothing more than an expression of anti-Phobos sentiments). They have no fondness for the Sun. It's no brighter than any other stellar object in their homeworld's sky, certainly not bright enough to dispel the permanent gloom, or disperse the clouds of carbon dust which shield the surface from the hateful stars.