QNP isn't a mod, but rather a much improved propulsion scheme which is used in a number of mods.
"Quasi Newtonian Propulsion", where Thrust Force = Mass * Speed
SE4 dosn't have a concept of acceleration, so Quasi is as close as you get.
Starfury has a limited acceleration model, though, and I made a mod for that which made the engines provide only turn rate and acceleration, while the speed of the ship was essentially unlimited.
Quite nifty, although it takes a lot of getting used to... very easy to hit the retros too late, and plow into the planet you are heading for.
