Update: There is now a wiki entry for jumpdrives, which supercedes this.
If I'm back to "matter stays in jumpspace even without a field bubble around it" then it's possible to launch projectiles through jumpspace, which led me to "what about fighters in jumpspace?"
(Actually "whaling boats" but that's effectively fighters.)
Chemical thrusters would work, even if Magical Antigrav Type Stuff doesn't (though ship-internal agrav does work... hmm), which then is problematic. Because if chemical thrusters work for a fighter, it would work for the whole ship, and jet-speed-in-jumpspace starships would easily be outpaced by rocket-speed-in-jumpspace starships.
Plus: if you only need a jump drive to get into space, you can have a "stargate" of a single giant hauler that pulls ships into space and lets them go, never leaving the system itself. That's (probably) not what I want.
So maybe chemical thrusters don't work? (Inertia not working feels like something that would have bigger implications though.)
I'm back to needing a field bubble, aren't I? Hmm.
Revised whaling
If whales are not sentient (or even detectibly more intelligent than a single-celled organism), it's going to be considered [more] okay to hunt them by all cultures. (Though Zhdez, for instance, are much less meat-oriented than other cultures and are not thrilled with the necessity.) This brings me back around to "no extended whaling voyages" unless:
Whales appear to migrate from map-south to north, though it's difficult to track individual whales since they avoid non-whaling ships, and whalers tend to put a permanent end to any migration for whales they find. More to the point, no new whales seem to be coming in from the south, meaning the Terran territories (terrantories) are almost whale-free.
The Inukari position is that Terrans have overfished, while the Zhdez position is that the whales are in fact moving, and that it's linked to the withdrawal of the Ancients from Charted Space. Terrans, meanwhile, have a fleet of well-armed ships who make extended northern forays to keep their ships supplied with exoplasm. On the principle that they whales are leaving, they try to fish as far north as possible, hoping to catch whales before they leave Charted Space.
The Zhdez are fairly certain it isn't overfishing, since they're seeing their own decline in whale numbers. They are focusing on alternative sources of exoplasm - both in figuring out where whales go when sounding/feeding, and in collecting less-efficient voidlife - and on finding alternative types of interstellar travel.
Terrans are, ironically, studying whales more thoroughly than anyone else (though this is one of the few areas they cooperate with Zhdez researchers).
The Inukari who take the problem seriously are working hard to figure out the link between the Ancients and whale migration - are the Ancients leaving for more whale-rich areas? Are the whales following the Ancients, who seem to have also moved north? Ancients have never demanded exoplasm as tribute, and it's not clear that's what they use to power their starships.
Great Old Ones
I've gone from thinking "maybe the realspace side of inter-system jumpspace is where the Ancients live" to "but that's also where the sea monsters are" to "hmm, maybe the ~~Ancients~~ Precursors are eldritch horrors?"
Probably not, but it's an idea I'm going to keep in the back of my mind.
Sea monsters
Update: There is now a wiki entry for voidlife, which supercedes this.
I'm noodling around with the idea that starwhales "sound" into some other dimension (whatever "realspace" means outside the correspondence zone of a specific system/universe). Which begs for the questions "what are they doing there?" and "what else is there?"
For the second, obviously: giant kraken. Or their analogs, at least. Something that "surfaces" out of nowhere to attack ships, possibly only in legend. After all, unless someone sees it there's no way of knowing what happened to a ship that simply disappeared. And if sea monsters only attack solitary ships, there aren't witnesses.
Trip length
Update: There is now a wiki entry for jumpdrives, which supercedes this.
Given my current parameters, there's a few limitations on how long a trip can be.
Life support is the obvious one. It's relatively easy to overcome just by choosing to, though your average passenger liner will not be equipped for an unexpectedly long trip (though it certainly will be prepared for reasonable delays).
Fuel is the big limiting factor for Traveller ships, and brightspace energy (I may have to change that name since I guess I'm waving goodbye to false stars in favor of currents) is limiting in one sense (cost) but less so in ship size/volume. (This lets whaling ships who are awash in energy keep flying where a commercial ship would find it a lot more expensive.)
A ship would have to transition between currents in order not to drop into a gate lens now and then, which again would be energy-intensive sometimes.
But if a J1 ship can just ride a J2 current for twice as long, this eliminates the isolation period of the Ancients' withdrawal. Maybe there's something about the currents that J1 ships can't manage? Too strong and it "blows out" the jump field, maybe? That does open some interesting possibilities: a J1 ship can perhaps sustain travel in a J2 current for awhile, but it's risky. And a J2 ship in a J1 current still can't go faster than the current.
So if my analogy is sailing ships, the jump field is just the sails. A storm can shred them and then you're adrift, but if you've got the canvas/energy (and are out of the storm) you can just put them up again. But a drifting hulk will eventually deteriorate. Unlike the oceangoing one, a derelict starship isn't so likely to sink (just get absorbed by a space-amoeba).
The sail analogy doesn't go too far though, I don't think I want solar-sail looking starships (even if it's just the field and not a physical structure.
Revising the jump field
Update: There is now a wiki entry for jumpdrives, which supercedes this.
There are two competing uses of the jump field, at this point in my theory: getting into jumpspace, and moving through it. I initially thought of this as being the same use: you're maintaining a bubble of realspace in an alternate universe, and shaping that bubble to convince jumpspace to squeeze you along like a watermelon pip.
If dropping out of jumpspace only happens in the lens of a gate, that changes the purpose of the jump field. If there aren't laws-of-physics differences between the two spaces, such that jumpspace life is basically normal matter (albeit with some handwavey magic energy fields), then a ship can stay in jumpspace indefinitely, permanent structures can be built in jumpspace, and so on, and I'm not quite sure that's what I want, and yet.
Maybe the problem is just that the alternate universe has normal laws of physics, but no native matter (hence: the void). Jumpspace creatures (or plants) are hungry for realspace matter and a stationary structure will get chewed to bits. Plus here's a strong enough current piped through the gate that turbulence will mean "stationary" around a system isn't doable. A ship could stay in jumpspace indefinitely but it needs to keep maneuvering even to stay in one place, and then you'll have to keep scraping the space-barnacles. But it miiiiiight be possible to build pirate stations in the doldrums. They'll need defended from wildlife and maneuvered to stay in position, just considerably less so.
Currents
Update: There is now a wiki entry for jumpdrives, which supercedes this.
Okay, here's my thought: the "currents" that pass through a correspondence zone all go the same direction, twisting and braiding into a bundle that fills the correspondence zone at right angles to the invariable plane. Planets (or any mass of sufficient size) cause a distortion in the correspondence zone, pulling it up or down out of the plane in a sort of dimple.
The correspondence zone is a big lenticular shape, and ships have to get far enough out of the way below the plane to enter jumpspace outside the zone, because once you cross the "lens" you are dumped out. The lens is incredibly thin, compared to its diameter; a 1G ship will take 12 to 16 hours to reach the edge of it. Attempts can be made sooner but one runs the risk of wasting field energy only to be dumped back insystem.
The current curves up and out from the lens and then branches, taking off in all directions, braiding, and corkscrewing around others. There are hundreds that go between any given J1 pairs, declining to tens between J6 pairs.
Currents shift over time, and where opposing currents encounter each other, cause turbulence. So does the ever-moving distortion of a planet in its orbit, meaning ships drop into the compressed but not yet turbulent current ahead of their destination. A ship that loses its jump field to turbulence may have a great deal of trouble reestablishing it.
Outside the prevailing currents, a ship can still find current to ride, though sometimes less predictably. Changing currents mid-trip is thus possible, though it will add time to the journey.
There are occasional doldrums, of varying size up to the great rifts between systems. Whales can cross them, because they can "swim" as well as passively use currents. Starships can do some of this, but it is incredibily power-hungry - though the whales' field manipulation is clearly less energy-intensive, a rift-crossing journey will still deplete their exoplasm reserves.
