I have known that this was proposed for a long time now, and I have always had trouble picturing how it would be effective. A nuclear blast in a vacuum would not be pushing the atmosphere or debris. It would just be the mass of the bomb itself pushing against the shield, which doesn't seem like that much. Or is this some effect like photons pushing a mass?
The million degree temperatures involved also might tend to be problematic (if the mass striking the plate is from close proximity to the detonation....). How would you armor the feed tube which ejects the bombs directly behind (and centered on) the pusher plate???
Rockets do not "push against" anything. The whole business is momentum transfer.
Focus the (blast)action in a certain direction.
Every action has an equal and opposite reaction, which is, in this case, thrust.
It isn't "pushing" against anything.
my understanding is that the pusher plate (steel plate several feet thick, IIRC) would ablate from the heat, sending atoms at very high speed rearward and causing the thrust.