Everything that I've read about NPP states that a pulse unit would be ejected on the average of one every second. To me, this sounds like an undoable objective. Getting the loader to load the pulse units, the firing mechanism to fire them, and blast door in the center of the pusher plate to open and close once a second for an extended period of time without breaking down or jamming seems to be pushing it.

Is this high firing rate just for the Earth launched system or for the system in general? A high firing rate would be needed to accelerate out of the planet's atmosphere and gravity well, but would it be needed in space? If the ship was launched in the weightless vacuum of space then wouldn't the momentum imparted by the pulse units be cumulative regardless of the frequency of them firing? A firing rate of one every minute or so would be much easier on the machinery.