Simplex started as a branch from Complex. It has combined features from Path To Victory as well as many other mods through a long history of R&D. This mod aims to excavate the full potential of the Homeworld 2 engine and it will simply blow your mind with incredible fun!
I don't know how your implementing the afterburner but I hope you remember that its only used to boost speed for a short period of time. In a space ship as you can't use air burning engines you could end up damaging the engines. Or maybe you could implement that somehow to make people concentrate, if you use the afterburner for too long then the engines cut out and the ship is damaged?
Yes, I didn't allow this boost to work for a long period of time (a few seconds at most). In fact, based on the working machanism of rocket engine, there would never be an afterburner for space ship, because the rocket engine itself is an afterburner to some extend (at least for conventional rocket engine). But whatsoever, this is a sci-fi mod, just imagine it works as Schnolf said :D
Its possibly like an auxiliary engine with a limited amount of fuel, so after it runs it needs to build the fuel levels back up.