What we really need are better ion propulsion systems. Even with a power source current ion propulsion systems are much slower than chemical rockets for short-t

What we really need are better ion propulsion systems. Even with a power source current ion propulsion systems are much slower than chemical rockets for short-term deep space missions like transit to Mars. https://en.wikipedia.org/wiki/Electrically_powered_spacecraft_propulsion https://en.wikipedia.org/wiki/Electrically_powered_spacecraf... Realistically, if we had good electric propulsion we could just slap a conventional fission reactor in there. We already launch plutonium on many deep-space missions for steady nuclear power. For now chemical propulsion is simply faster and more reliable, electric propulsion is still in the early stages, and there are many other problems to solve in human spaceflight.