Last weekend I created a draft design sequence. I can tell you that no matter how long or hard you think about your game's ships (vehicles, in this case), you don't know them until they tumble out of a big clunky spreadsheet. When I started, I was planning on very hard science-based travel. Maybe because my original inspiration was my 5-year-old's efforts in Space Simulator and Kerbal. Ultimately, unless you want a game about vast tanks of reaction mass, tiny pods, and months of travel, it takes away more than it gives. So I have handwaved in some helpful exceptions to current physics.
We were wrong! You can tweak the Higgs field. Using the Mach-Fontier inductor, you can fool your space vehicle into thinking it has only 1% of its inertial mass". Combined with the super-high-efficiency Quan-Ebrahimi fusion engines, you get weeks or months of 1g thrust. Thank you, magnetic reconnection! Cheers, magneto-plasmic surrogation!