Very interesting design....however there is a flaw I fear. The reliance of said propulsion system on concussive force.
With an atmosphere this is a feasible design...in a vacuum not so much. On earth most of the destructive power from a nuclear device comes from the concussive backlash of the atmosphere responding to such a massive amount of heat in such a small amount of time (then of course the fall out afterwards but leaving this out).
In a vacuum this would not exist.... detonate a nuclear device in space and you will have a really really hot area for a minute...a very bright flash of light...then all will be well again.
Very interesting concept though....
Put simply, no, no, no, that is entirely wrong.
The nuclear pulse propulsion concept doesn't necessarily rely on the concussive wave of an exploding nuclear device, but rather the shaped directed charge of particles resultant from that explosion which will be hitting the ablation plate at several hundred thousand miles per hour upon detonation.
Cumulatively, this translates to a massive transferal of kinetic energy from the pushed ablation plate into the shocks which are subsequently compressed as the craft is moved forward.
The same concept applies to rockets in a vacuum, newton's third law. Every action has an equal and opposite reaction. In other words the force of the rocket pushes itself. Whether or not that takes place in an atmosphere or in a vacuum is completely irrelevant. Hence why objects bear the same mass on within a micro-gravity/zero-gravity environment upon impact with other objects as they would with on earth. Gravity just mediates the severity of such an impact's force when falling, but velocity in space performs the same action.
Though the concept of Project Orion wouldn't and likely never would be 100% efficient (if even 80-90% efficient), the mechanism by which it would attain its maximum potential velocity relative to the speed of light is by an order of magnitude MUCH more efficient than rockets today are in reaching hypersonic velocities either in the atmosphere or in vacuum.
The key is in energy density. Chemical fuels simply do not and never will have that potential... aside of nuclear salt water rockets or hydrogen fusion propulsion designs, but neither of those latter achieve propulsion by combustion, but rather through sustaining fission or fusion which are entirely different from chemical processes.
Our very in-depth conversations on technology and space are awesome... it really enriches me, and I appreciate that.
I think you will like reading the following articles. However unfortunate it may be that their funding was cut a long time ago. It could have given a Saturn-type rocket the push it needed to reach mars in a fraction of the time than possible with chemical engines.
American
https://en.wikipedia.org/wiki/NERVA <- Tested, completed all tasks and was a success.
https://en.wikipedia.org/wiki/Project_Rover <- Used NERVA engine.
https://en.wikipedia.org/wiki/Project_Timberwind <- Was suppose to be a refined version of NERVA, no test engines were build.
Russian
https://en.wikipedia.org/wiki/RD-0410-----------------------------------------------------------------
♫♪Sometimes
I feel like I want to live
Far from the metropolis
Just walk through that door
Sometimes
I feel like I want to fly
Reach out to the painted sky
A prisoner to the wind
A bird on the wing♫♪