<Things were a lot looser forty years ago when they were working on Orion. That technology was brought to us by the same people who assured us that we could survive a nuclear war by digging a shallow trench in the dirt and covering it with plywood. It's not a bad thing that the nuclear safety bar is a lot higher today than it was then.

I would have been a lot happier if some of the many atmospheric tests had been used to actually do something useful like launch a large space station or Mars mission. Oh well.

And yes, a trench covered with dirt would save millions of lives in a nuclear exchange. Not everybody lives on ground zero, and I know something about fallout. But that' another story.

NASA's going to be fully mindful of the need to prove that any nuclear propulsion system it builds won't have harmful side effects. It'll have to satisfy the majority of environmentalists, though I'll concede that the more extreme environmentalists will never see beyond the word "nucular".

Nothing nuclear will ever satisfy environmentalists, but one hopes we can go ahead anyway. I really think we need this technology.

It won't be hard to prove the safety of a propulsion system intended for use only in space--vacuum is a powerful prophylactic. The sticking point is going to be construction and launch, and there we have the precedent of almost four decades of RTG use to go on.

One technique would be to launch the reactor and fuel separately, with the fuel maybe being launched in several subcritical packages. The reactor would not become "live" and highly radioactive until all the parts were assembled in space.