The Variable Specific Impulse Magnetoplasma Rocket engine (VASIMR engine) is an engine currently under research development by NASA and other space agencies with the capability to carry people to Mars in under 40 days. It is also planned to be used on the ISS for orbital adjustments. In this engine, electricity is used to ionize an inert gas like Xenon (H2 is better since it is a waste product on manned space stations like the ISS. Hydrogen gas is also one of the most common gases in the universe, so a craft that uses Hydrogen fueled VASIMR engines could potentially refuel at any planet with Hydrogen in its atmosphere.) which heats it enough to turn it into a plasma. this plasma is propelled down a tube surrounded by magnets. The VASIMR engine has an isp of 5000 seconds (not recreatable in game without mods).
Obviously, I can't recreate this engine's performance, but the concept is pretty cool.
I make cooler version is “Wayne Infinity’s VASIMR pack”