[InclinedPlane]

Project Orion was only a waste of money in the short-term. Long-term nuclear pulse propulsion will probably be put to practical use. Potential Earth impacting asteroids are fairly easy to protect against, you spend a lot of effort cataloging them and then you find the ones that could hit Earth 50, 100, even a thousand years in the future and then you go and you nudge those asteroids just enough to put them onto a non-impacting course.

But there are also long period comets that come in from the oort cloud. We may never have the technology to fully catalog all those objects (out to thousands of AU up to a light-year distant from the Sun). Which means that even our very much more technologically advanced future selves will almost certainly still be faced with the potential problem of having to intercept and divert an Earth-impacting oort cloud comet that has wandered into the inner Solar System. And to do so not with a century of lead time but with only a few years. And, worse yet, to have to trudge out to the outer Solar System in the first place just to have a chance to divert the thing in time.

This calls for a vehicle with a stupendous amount of thrust and delta-V capability. Precisely what nuclear pulse propulsion excels at. More so, the "pulse units" can do double duty by being used to divert the comet (using thrust generated by ablation from stand-off explosions).

So ultimately research into nuclear pulse propulsion is likely to be key to preventing the destruction of human civilization on Earth.