(Love love love the level of traffic!!)
Ok, here's my take on it.
Early Jump Drives need a gas bubble to inflate the portion of space time. These are refined more and more allowing for longer jumps - transiting "deeper" jump spaces with stranger physics.
Just like early J1 and J2 drives require a "backstop" endpoint to precipitate them out of J Space, and at TTL 12 that is overcome allowing for deep space jumps.
At TTL 16 a breakthrough in jumpspace physics allows for *energy* fields to provide the bubble, at hideous levels of power. The only engines powerful enough are antimatter.
However due to the energy density of antimatter fuel, at that higher TTL you can carry fuel for many jumps.
Higher TTL drives can do other things, like shorten transit times to days, or open a jump space conduit and squirt radio through it.
At obscene TTLs you can 'squirt' physical objects like missiles/HK robots etc.
I like the idea of smaller jump ships being possible - just 2dt of drive and 10dt of fuel is required.
Just my headcannon for jump drives :)
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