Nuclear pulse propulsion is certainly interesting, but it would face the same problems nuclear energy itself faces - it sounds scary and honestly would only be useful once in space for the most part because of it.
Indeed. The concept of lifting up a megasized rocket directly from earth could work out in the 50s or 60s, but not today. Anyway, if we are to scale out space travels, I think we need to think beyond chemical rockets (explosive or conventional).