I'm writing this as a creative outlet. The basic idea occurred to me this morning, and I fleshed it out somewhat at work. Warning: I will be linking to TVtropes where appropriate.

Basic Conceits & Tropes
I'm aiming for a class 3 to class 4 on the Mohs Scale of Science Fiction Hardness, with the possibility of occasional dips into class 2. Faster-than-light travel is a fact, but not as casual as, for example, Star Wars. Most starships, I think, will be owned by governments and Mega Corps. I don't think I want to portray the megas as being quite as evil as they are in cyberpunk and other dystopian genres, though.

I'm leaning toward Absent Aliens, with a strong possibility of Transhuman Aliens. The main part of the setting, the Leonine Empire (more on that in a bit), will have a technology level well below that of Star Wars or Star Trek: FTL is the "One Big Lie" in that part of the universe. Weapons are mainly kinetic and explosive in nature, no energy shields, etc.

The history of the Leo Cluster (where the Leonine Empire is located; see what I did there?) will include a dark age: widespread interstellar warfare led to most, if not all, planets being bombed back to... well, not quite the Stone Age, but definitely to a pre-industrial state. This allows me to do a couple of things: it justifies having planets within the Empire with widely varying tech levels; it allows for the existence of Lost Technology and even the odd Lost Superweapon; and it allows polities outside the Empire to have significantly more advanced technology, thereby giving it a natural boundary and a reason to stop expanding.

On the subject of foreigners, I've got two extra-Imperial "states" so far (for a given value of "state"): the Solar Commonwealth, and a human-spawned AI that bootstrapped itself to a godlike level of intellect and power, tentatively called the Synthetic Intelligence, or SI for short. The Solar Commonwealth has technology significantly in advance of the Empire, and embraced transhumanism wholeheartedly a long time ago. Its people, while still being recognizably people, are mostly inscrutable, due to a combination of an extreme culture gap and altered thought processes. The Commonwealth as a whole is very inward-looking, though there may be individuals and groups taking an interest in foreign affairs (dun-dun-dunnnnn!). The SI will be the setting's chief source of phlebotinum, the assumption being that the SI's enormous processing power allows it to model reality effectively one-to-one: it doesn't need to build labs and spend time prototyping, because its mind is the lab and it can run as many experiments as it wants, as fast as it can think through the processes. Consequently, the SI is the setting's Sufficiently Advanced Alien, to the point of SI artifacts being basically Magic From Technology.

Which leads neatly into the subject of psychic powers and other magic-analogues: there aren't any. At least, none that are usable by or available to the player characters. I'm thinking that anything that can kill you with its brain is going to be at least a low-grade Eldritch Abomination: I want the PCs to think, "Holy fuck, how are we supposed to counter that?!" rather than, "Cool, let's see if we can recruit him."

Next post: a brief outline of the Leonine Empire.

The Leo Cluster: A (very) Brief History
~1,000 years BP (Before Present; actual in-universe calendar TBD): Tensions among the worlds of the Leo Cluster erupt into full-scale warfare. Over the course of several decades, all spaceborne habitats are destroyed and most planets bombarded to a pre-industrial state. All known starships in the Cluster are destroyed, rendered derelict, or simply lost.

~950-500 years BP: The Interregnum. Technological civilization slowly rebuilds.

~500 years BP: FTL travel rediscovered by several worlds more or less simultaneously. Contact reestablished with most planets. Tentative peace accords reached.

~450-400 years BP: Tensions in the Cluster mount. Finger-pointing, vis-a-vis the Interrregnum, appears to be leading up to renewed warfare.

~400-375 years BP: A warlord named Richard Stahl comes to power on planet New Oxford. Stahl exploits New Oxford's military power by conquering most of the Leo Cluster in a series of lightning strikes.

~375 years BP: Richard Stahl declares himself Richard I, Emperor of the Leo Cluster. The Leonine Empire is born. Stahl is a brutal tyrant, caring for little beyond his own power. His son, Richard II, proves slightly wiser, and Richard II's daughter, Catherine I, is wiser still. In this way, conditions slowly improve.

~300 years BP: Experiments in computer sapience bear fruit in the form of a recursively self-improving intelligence, called the Synthetic Intelligence, or SI. SI absorbs all known historical records, including recovered pre-Interregnum data, in a matter of minutes. It expands through the interstellar communications network, seizes control of all fusion power plants on every Imperial world, and threatens total devastation unless it is allowed to depart Imperial space. Imperial authorities call its bluff. The SI destroys the industrial center of Rowan, on planet Wyndham's Hope. Estimated death toll: 26.4 million. Imperial authorities immediately capitulate. The Imperial Fleet commandeers the interstellar freighter Butcher Bay and offers it to the SI. The SI uses teleoperated machinery to install a self-designed computer core aboard the Butcher Bay, then uploads itself into the ship. The Butcher Bay departs for parts unknown. Rear-guard programs left behind by the SI to cover its retreat self-erase, returning control of all power plants and interstellar communications to the Empire.

~300-100 years BP: Discontent with Imperial rule rises slowly but steadily. The Lion Emperors descended from Richard I prove mostly capable and reasonably popular, but many worlds long for a return to sovereignty. Separatist movements break out in several parts of the Cluster, and are ruthlessly stamped out.

~50 years BP: Imperial reconnaissance ship Sassenach reestablishes contact with the SI 137 light-years beyond the Empire's coreward boundary. The SI has established itself in several systems and is embarked on several megascale engineering projects, including a Dyson sphere and at least one matrioshka brain. The Sassenach's report is classified at the highest level: the fact that the SI exists and is remaking entire star systems to its own agenda is a military secret known only to the Emperor and his Privy Council.

~10 years BP: Emperor Erik III institutes wide-reaching political reforms, aimed at converting the Empire from an absolute to a constitutional monarchy. He is assassinated at the age of 47, ostensibly by separatist terrorists, but widespread rumors place his death at the hands of disaffected nobles fearful of losing power. His daughter, Lisbeth II, is crowned Lion Empress at age 22.

~10 years BP to present: Lisbeth II continues her father's reforms, making no secret of her determination that the line of the Lion Emperors will end with her. Her efforts gain her widespread acclaim and popularity among the commons, but Imperial nobility scheme behind her back. Separatist sentiment is on the rise again at the fringes of the Empire; many are unwilling to wait for reform and advocate violent rebellion. Brushfire wars erupt on several planets, with one side or the other (sometimes both) requesting Imperial intervention.

Notes
I've tried to populate the Cluster with numerous plot hooks and campaign opportunities. You want political intrigue? Get involved in Empress Lisbeth II's reform agenda, or back the nobles who want her deposed and/or assassinated. Would you prefer a more action-oriented game? Head out to the fringe and help stamp out one of the civil wars going on. Is a more Star Trek-like explorers-vs-the-unknown plot to your liking? Put the PCs on a recon ship headed into extra-Imperial space. You might even meet the SI! And get assimilated by it. Just kidding. Maybe.

For some reason due to brain farting, I had to read the title several times to not read "a Hebrew space setting" and have been really wondering how THAT was gonna work out.

If it's space Jews you want, read Dune. Well, space Jew-Muslim-ninja-pirate-zombie-robots... wait, I got sidetracked there. Sorry.

Character Options
Now we're getting into areas where it's hard to be specific about things, mainly because I don't really have a specific system in mind yet. Nevertheless, forging ahead...

I'm going to assume, for lack of a better starting point, that the PCs are officers in the Imperial military. Right now, I'm thinking there are three branches of service, roughly corresponding to the classic fighter-mage-thief triad. No, I don't want a class-based system (at least, I don't think I do, although there are things to recommend it); possibly each branch will give discounts on appropriate skills and whatnot.

Her Majesty's Imperial Star Fleet: The biggest and most expensive segment of the Imperial military. HMISF (colloquially, "the Imperial Fleet," "the Fleet," or "the ISF") accounts for all Imperial naval assets (obviously) and most aerospace assets. The Fleet fills the "mage" side of the triangle, except there's no magic. Fleet officers receive a great deal of technical training and education, since they expect (rightly or, occasionally, wrongly) to spend most of their careers aboard one or more starships. The Fleet also encompasses Her Majesty's Imperial Space Marine Corps, who are more combat-oriented than regular Fleet officers but more commando-like than Army characters. Marines also receive a fair bit of technical training, but also learn techniques geared toward infiltration, ambushes, sabotage, that sort of thing. Marines also specialize in ship-to-ship boarding actions and defending against same. If your character concept is a hacker, engineer, all-around gearhead, he probably went to the ISF Academy. If he's an assassin, ninja, sniper, or any sort of combatant with a sneaky bent, he's probably a jarhead. Hoo-ah!

Her Majesty's Imperial Starborne Army: The Fleet conquers star systems; the Army conquers planets. HMISA ("the Army," or "the ISA") is all about straight-up combat. They have their own Special Forces units, but mostly when the Army comes to your neighborhood, they do it in force: tens of thousands of power-armored troopers with tanks, artillery, and some aerospace support. Army characters are proficient in most forms of armed and unarmed combat, and do best as part of a fireteam. They have some technical skills, mostly related to the care and feeding of various types of guns and combat vehicles, but mostly what they do is make live things dead, and whole things fragmentary. Army officers also learn skills and abilities relating to leadership under fire. I think of them as both frontline combatants and natural party leaders.

Her Majesty's Imperial Intelligence Service: Yep, in the Leonine Empire, the spies are in the military. Here we have our "thief" characters: spook officers learn a little about close combat, but their real strengths are in stealth, disguise, and misdirection. Think Michael Westen, only not burned. They're the con men, the fixers, the agents provocateurs of the Imperial war machine. They're good at learning things they're not supposed to, and at feeding false information to the Empire's enemies.

Notes on Space Travel
Let's start big, both literally and figuratively. I don't want interstellar travel to be casual: no Millennium Falcons. The Solar Commonwealth might be able to build starships the size of a house; the SI almost certainly can; but in the Empire, the only power plants capable of supplying the enormous energy required to span the stars are, well, enormous. I know I want starships to be big, but I've gone back and forth on exactly how big. I initially thought that the island of Manhattan would make a good template, at least in terms of size, at 21.6km long by 3.7km wide. If we make the ship about a kilometer thick, we're looking at a nominal volume of 79.92km³. I'm of two minds, here. On the one hand, I'm not really going for the "spaceborne city" thing. I want a definite "vehicle" feeling for starships, rather than "mobile setting." As much as I love Iain M. Banks' Culture novels, I think his starships are too big for the Empire. On the other hand, I want ships to be big enough that a rogue starship is a weapon unto itself, even before taking into account any actual weapons it may be armed with. I want the news that an ISF starship has arrived in-system to be a definite "Oh, crap" moment for all but the most powerful antagonists, and a combination "Here comes the cavalry"/gunship rescue for the PCs.

I think I just have to bite the bullet and say that most starships are about ten kilometers long.

While writing this, a thought has struck me. I think I have a way to make starships big without them becoming settings unto themselves, and it's this: a starship is a power plant, a hyperdrive, and not a whole lot else. I'm thinking a crew of 50-100. How do you get away with flying something the size of a middling geographical feature with only a hundred people? Simple. The ship is mostly a skeletal mooring frame. Freighters, passenger liners, the odd private space yacht, pay the starship's owners to haul them across the gulf between stars. The starships themselves act like trains, basically: each one flies a circuit among a couple dozen inhabited systems or so, staying a few days in each system to take on and offload lesser ships.

Naturally, ten kilometers of truss strewn with spaceships has a bit of heft to it. I don't think starships have much in the way of maneuvering capability, with the possible exception of military starships (more on those in a bit). They jump in (transit zones being well-mapped, and located reasonably convenient to all major habitats), shuffle ships on and off, and jump out.

Military starships are a bit different. They're still mostly mooring framework, but the framework is studded with weapons, the best sensors money can buy, and sundry other unpleasantness. An ISF supercarrier is the command ship for a task force capable of conquering whole star systems. They arrive fully loaded: battleships, troop carriers, destroyers (missile racks mounted on engines, basically), etc. These are deployed infrequently; most ISF ships travel on commercial starships like everybody else.

something tells me you've read the evolutionary void recently

Actually, I haven't read any of the Void books. The only Peter Hamilton novels I have are the Night's Dawn books, Pandora's Star, and Judas Unchained. I quite like Hamilton's work, I just haven't gotten around to The Dreaming Void.

Mel Brooks directs another sci-fi movie?

Spaceballs II: The Phone Wars? I'd pay money to see that.

My focus for this project has shifted from RPG to wargame. I ordered a rulebook today for a system called Starmada. From what I can tell, it has something like the right combination of flexibility and setting-agnosticism to let me run a campaign of starship combat in the Leonine Empire. I might have to back off from the idea of starships-as-carriers to a more traditional naval model, but I think I can live with that. I'm looking forward to finally getting to grips with the setting.

The setting sounds interesting so far. The carrier jumpships sounds like the Guild freighters (?) from Dune. Which isn't to say that it's a bad idea; I think it works for what you're trying to do. For the Army, what's the tech level. You mentioned power armor. Dropships of some sort will be a necessity for the soft equipment at a minimum, since it sounds like the motherships will be too big to land on the planet. Are gravitics available? If so, you could borrow a page from Traveller and have grav tanks that can do double duty as impromptu CAS and solve the problem of getting the tanks dirtside.

Gravity control/generation is certainly possible for the SI; maybe for the Solar Commonwealth; definitely not for the Empire. ISA dropships conform to the BattleTech mold, I think: spheroids or aerodynes carrying soldiers and war machines, most of which are air-droppable and some of which are space-droppable. I think all ISA infantry are power-armored. Some, the equivalent of US Army Rangers, are specially trained and equipped to be dropped from orbit: their job is to secure landing zones for the dropships bringing in the heavy firepower.

One thing to remember is that there is no such thing as a planetary assault without aerospace supremacy. By the time the ISF takes orbit around a planet, they've already destroyed everything on the surface capable of reaching them. So when the Rangers start dropping, they're screened by ISF fighters and probably preceded by orbital bombardment.

Apologies for the necrothread, but I've been thinking some more about this setting, particularly about giving the PCs a starting point and a reason for them to know each other.

The Joint Office of Special Investigations
JOSI began its life in the early days of the Empire as a solution to the natural tendency of bureaucracies toward turf wars. Its mandate is to handle investigations involving overlapping jurisdictions within the Imperial government. Since no agency would countenance being under the oversight of its competitors, JOSI ended up being a military operation; and, perhaps inevitably given the nature of its job, became a backwater posting with little chance of recognition or advancement. JOSI is one of those commands where careers go to die.

Which is exactly how its current CO wants it. Major Maya Delacroix was once a rising star in the Intelligence Service, a bright, canny, driven woman who seemed on track to reach the very top. She ended up in the cul-de-sac that is JOSI after pursuing a lead in an official-corruption investigation that led her to the door of an influential member of Parliament. Politics forced the IIS to shunt her out of the limelight, and Major Delacroix's fast-track career stalled abruptly.

Major Delacroix, however, is the type of person to see opportunity even in adversity. As a spy, she knows that the disregard of one's enemies can be a powerful asset in itself. As a highly competent officer, she has enough pull in the service to have her pick of Academy graduates every few years. As a "disgraced" officer, her command is largely ignored by those bodies nominally charged with its oversight. These facts, taken together, have allowed Major Delacroix to assemble a small but extremely capable group of junior officers, which she wields like a scalpel against the Empire's enemies.

Drawn from all three branches of Imperial service, Major Delacroix's people travel all over the Empire, sniffing out trouble. Many times, they are able to put an end to it before the problem grows too large; other times, Major Delacroix finds it necessary to call in a favor from the Fleet or the Army, to supply heavily armed backup to her little band of troubleshooters.

The first CO of JOSI, Fleet Captain Yusuf Abdul Hassan, was a fan of ancient Earth pop culture; it was he who started the tradition of referring to JOSI agents as "Pussycats."