That's not really related though. I'm asking "what if you build a gun with nukes as propellant?", not "what if you build a plane that rocket jumps through air/space?". The idea is to impart the highest fraction of a single bomb's energy onto a payload. Orion is pretty wasteful in terms of energy conversion.

Orion requires quite a few detonations, though; even with a massive craft (much of which is pusher plate and shock absorbers) to absorb the impact, you have to use fairly low-yield bombs and each only provides a relatively short period of thrust. You could possibly design something that takes higher yields (especially higher relative to the vehicle mass) that would survive reaching orbit on one detonation, but it would be subjected to extreme acceleration - the kind that would crush any satellite launched thus far - and I suspect there might be too much risk of tumbling given the non-uniformity of the atmosphere.