Metallic Hydrogen would be great to have in SR2, it is unbelievably more powerful than liquid hydrogen while also offering more ISP than even Ion Engines, but adding this will also require a new engine cycle. An electromagnetic engine cycle is about what its name implies, it basically directs the metallic hydrogen fuel using electromagnets to propel whatever spacecraft the engine is installed on.
@sacr3dbac0n0 preferably I wanna be able to do things without requiring mods, especially since I'm on mobile and my potato PC can't handle a game like SR2
Electromagnetic engine cycles are simply the only engines that can use metallic hydrogen as the fuel