Thermonuclear Orion could (on paper) reach 10% the speed of light. Proxima Centauri in about 50 years using technology contemporary with the Beatles and Woodstock.
This is why I have trouble dismissing the Fermi paradox. Either intelligent life that can engage in space flight is very rare (as in less than one per galaxy per billion years) or we are in a wildlife preserve or a zoo.
Project Daedalus could reach 10% speed of light. But that didn’t use thermonuclear bombs but laser-pumped inertial confinement fusion. It also didn’t use physical pusher but magnetic nozzle. We don’t know how to do them with our technology but should be possible. There are followons that are more doable but slower.
I have seen Wikipedia quote 10% for regular Orion but not finding any sources. I find that speed unlikely with all the trouble that Daedalus and others went through to get interstellar pulse rockets. I see 6ksec impulse for could-build-now Orion, 100ksec for theoretical improvements, and Daedalus would be 1Msec. Regular Orion probably maxes out at 1%.
Fission Orion is infeasible for interstellar because need huge quantities of fissionables, maybe 10-100x weight of ship. Fusion has advantage of using cheap elements.
This is why I have trouble dismissing the Fermi paradox. Either intelligent life that can engage in space flight is very rare (as in less than one per galaxy per billion years) or we are in a wildlife preserve or a zoo.