Check the Orion project (Freeman Dyson's son wrote a good book). We could have been further out than Mars... 40 years ago. :-( The motto was "Mars by 1965, Sat

Check the Orion project (Freeman Dyson's son wrote a good book). We could have been further out than Mars... 40 years ago. :-( The motto was "Mars by 1965, Saturn by 1970" (but that was probably optimistic... by maybe five years or so. :-) ) And sure, there was talk about a failed launch increasing the background radiation by 1%. Some cancer risk would arguably be cheap to get an industrial infrastructure outside the atmosphere. (Also note the implications for the Great Filter theory regarding the Fermi paradox. With a bunch or Orion launches starting in the 1970s we could have viable colonies somewhere between now and 2030. So any big catastrophe as filter would need to sterilize a whole solar system, not just a planet.)