Project Orion motto: Mars by 1968 Saturn by 1972
Had that happened, there were inter-system versions to be followed by interstellar versions.
But like the NERVA, it was killed due to a failure of political will - something we still suffer from today; and by a need for politicians to retain power over individuals - something they would lose in a full-on deep space manned effort.
Unlike today’s concepts with a crew of a few and years to make a trip, and likely one way at that, the Orion worked better the bigger it got. So trips would be measured in days or weeks in the inner solar system, the outer in months. Crews in the test vehicle were 20 or more, water would ring the ship - insulating the crew from rays and providing hot water showers on demand.
The interstellar version would be crewed by hundreds for trips lasting years - but no where near the length of time for similar destinations using ion/plasma/solar sail/chemical. Only nuclear power of this sort could make trips to the nearer stars and back in a reasonable time frame.
One problem was that there was no way to steer the vehicle precisely - something which could have been solved had it gone forth. The real big problem was the one man who specialized in designing very small low yield fission bombs refused to make more and left the field.
Would this think spew radioactive material exhaust all the way there and back?
Do they make a catalytic converter for that?