Do you acknowledge the fact that interstellar travel entails more than just speeding up and slowing down? Because that's what Dyson would be telling you if he were here.
One of the main unsolved problems is the electromagnetic shielding, both front and back (as you need to turn to decelerate). Even at 0.08c every speck of interstellar dust has enormous impact energy, far worse than the radiation of your own bombs. AFAIK this is unsolved.
it's 35% of the fission energy released by totally fissioning 1g of U-235!
i.e. I don't know whether this it's feasible to just have a heavy water & lead shield, as 0.1g is fairly optimistic to be the heaviest particle hitting you. Already at this size we're in range of tactical nuclear weapons.
