Last night I was thinking about a story, and came up with yet another variation of FTL drive. This one's not as simple to operate as the last one, but it works.
Basically it's six hours per light year, but you can only make a jump of about twelve light years before you must return to normal space. It's possible to go farther, but if you do you are risking inversion.
When a ship makes the jump to FTL drive, it is via a process which requires energy to maintain (call it "C-plus excitation", a phrase I've borrowed from some SF short or another). Shut off the drive, the ship reverts to whatever velocity it had before the FTL drive was switched on. This is normal and just and proper.
But if something--a starship, say--undergoes inversion, it becomes impossible for it to exist in Einsteinian space any longer. The people aboard the ship notice no immediate reduction in their standard of living; they go on breathing and metabolizing exactly as they did before inversion. The problem is, it requires an inordinate amount of power to return it to E-space, because the Laws of Thermodynamics must be satisfied; it's therefore impossible for the inverted starship to return to E-space at all, let alone long enough to resupply, and wherever it got the energy to place it in a permanent state of C-plus excitation, the energy required to reverse that--however temporarily--must come from somewhere and it must necessarily be greater than the original energy input. Eventually the ship runs out of consumables like food and fuel and everyone dies, leaving the ghost ship to circle the universe approximately forever at six hours to the light year.
An undesirable outcome, in other words.
It's therefore easy to see that in this universe, along the routes of longer runs there would be waystations at approximately twelve light year intervals, all moving at the typical departure speed. Hotels, casinos, fuel stations, all the comforts of home 'way out in deep space.
This is a pretty interesting idea. One could set a story at one of these way stations. One could set a story on a ship that has overshot such a station and is without fuel. There are so many things a person could write here.
...what I need is to become Birefringent Man, so I could send one copy to work while the other one stays home and writes all this shit. WTF.