This may be a somewhat unpopular opinion, but when dealing with cinematic or superscience propulsion systems, I actually find it's easier and more efficient to work backwards.
I took a crack at this a while back for my own space opera setting (which never got off the ground but that's neither here nor there). Instead of looking at the available options in the various
Spaceships books and building a setting around it, I decided on certain standard metrics and then made my own custom propulsion drives based on those metrics. Things like:
- How long do I want it to take a ship to travel across a star system?
- How long should a ship be able to burn for on one fuel tank?
- How many Reaction Engines/Fuel Tanks should be the standard on typical freighters, q-ships, etc?
- How expensive should it be to refill a fuel tank?
Once you've got a decent amount of answers for these questions, not based on existing drives but based on how easy, fast, and economical you want space travel to be, then you can start assigning numbers to things like:
- How much delta-V does a single fuel tank provide?
- How many G of acceleration does a single reaction engine provide?
- How expensive is a ton of fuel?
I find that when it comes to mechanics, it's more important for them to fit the
style of game you want to play rather than adhere strictly to realism. So long as it remains internally consistent and gets you the results you want, who cares, right?
Jinumon