Interstellar exploration, nuclear fusion engines, warp drives, solar sails and antimatter annihilation thrusters.

More star systems would be cool, but to get there, we need far future propulsion. Solar sails could be used for lightweight probes. They could be cheap compared to these other methods of propulsion, require no propellant, but only be usable on ridiculously light probes. Nuclear fusion engines would be nice as a higher-efficiency and thrust but higher mass and cost version of the nuclear thermal engines, warp drives would be good to get lightspeed travel to other stars and planets, but would be pretty heavy and ridiculously expensive. The idea with warp drives is that getting an encounter would be infuriating, because you can’t use a ‘low throttle warp drive’ so you would have to go full throttle with perfect timing, so I propose you just select a planet, moon or star, select a ‘warp button’ and you travel so fast, you are propelled there in a straight line, not an orbit. Antimatter annihilation would be somewhere between the two. Far more powerful and efficient, heavier and more expensive than Nuclear Fusion, but not as much as Warp Drives. However, they would each have their own niche. In sandbox, warp drives should not make antimatter annihilation and nuclear fusion obsolete, and the same goes for career mode once you’re rich enough. I don’t have ideas for how you could make the other three non-obsolete, but it’s fine.