Project Orion

The History Channel had an interesting video clip of a little known project conducted by the US Airforce in the 1950s called "Project Orion." The information was obtained thru the freedom of information act and, according to the channel, the project went far further than anyone ever knew. The goal was to develop technology designed to move mankind to a distant planet in the event of a catastrophe on earth. It lasted for about a decade and the film clip shows a facsimile of a rocket being propelled upwards by a series of explosions behind the rocket itself. The people behind the project were quite serious and, given what they uncovered, it might not be necessary to reinvent the wheel relative to interplanetary flight. More:
https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion)

Yeah, I was aware of that; they did intriguing small-scale experiments that demonstrated the principle quite nicely: The vehicle (in the limit) is accelerated by a series of impulses, rather than continuous burn. If the impulses are literally nuclear, efficiency can be good. Protecting the crew from getting hammered is theoretically possible... but damned challenging. Reminds me of some ramjet contrails that are beaded/staccato.