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I’m not an expert but I’m pretty sure the only way to orbit via nuclear is riding the shockwave of one or more nuclear explosions. There was a program to develop one called Project Orion. https://en.m.wikipedia.org/wiki/Project_Orion_(nuclear_propu...

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No, nuclear thermal rockets could be launched from the ground. That was the plan with NERVA, which was a pretty serious attempt to develop the technology in the early seventies. A nuclear thermal rocket engine 'looks' like a rocket engine, but there's energy from fission in the combustion chamber.

I didn’t know about NERVA, thanks for the correction!

NERVA was targeting thrust to weight ratios of <5, though - which isn't high enough to lift off of the ground with. Makes a fantastic upper stage engine, but a rather useless first one.

And more specfically, it was being a proposed as a replacement for the S-IVB, the third stage of the Saturn V. Early maps (like the one shown at https://www.hq.nasa.gov/office/pao/History/SP-4204/ch11-8.ht... ) show the Nuclear Assembly Building, along with three pads, at Launch Complex 39, which launched the Saturn and Space Shuttle, and now launches the Falcon rocket.

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