I was around when they killed the original Project Orion in 1964 - Project motto: Mars by 1965, Saturn by 1970. Interplanetary model would have been 10,000 tons, crew 150. 3 days to Mars. Cost same or less than Apollo
Interstellar model would have been 40 million tons, 1.5 years to Alpha Centauri.
Killed by Government inter-agency infighting, NASA Apollo conflict, perceived treaty obligations, lack of political leadership. “...the first time in modern history that a major expansion of human technology has been suppressed for political reasons.” - Freeman Dyson.
Unfortunately, not the last...