If the slightly insane Nuclear Salt Water rocket can be pertectec then couple percent light speed might be doable even without complex exotic tech: https://en.

If the slightly insane Nuclear Salt Water rocket can be pertectec then couple percent light speed might be doable even without complex exotic tech: https://en.m.wikipedia.org/wiki/Nuclear_salt-water_rocket https://en.m.wikipedia.org/wiki/Nuclear_salt-water_rocket