Is NASA Necessary?

This week, after announcing a $104 billion plan for returning to the Moon for no particular reason, NASA Administrator Michael D. Griffin explained why money for rebuilding New Orleans should not be diverted from his budget:

There will be a lot more hurricanes and a lot more other natural disasters to befall the United States and the world in that time, I hope none worse than Katrina. But the space program is a long-term investment in our future. We must deal with our short-term problems while not sacrificing our long-term investments in our future. When we have a hurricane, we don't cancel the Air Force. We don't cancel the Navy. And we're not going to cancel NASA.

I am a science fiction fan and space enthusiast who hopes NASA critic Robert Park is wrong when he says "human space exploration is essentially over." But that does not mean I am prepared to force other people to fund my dreams. I see a distinction between the armed forces and NASA that Griffin seems to be missing: The Navy and the Air Force protect us from our foreign enemies, a central function of government for anyone who concedes the legitimacy of government at all, whereas NASA spends a lot of money on projects of dubious scientific value that are supposed to make us feel good. Given the relatively low cost of the unmanned missions that (as Park notes) offer the biggest scientific payoff, and given the emergence of a launch industry for both commercial payloads and space tourists, it seems NASA is necessary mainly to pay for projects that are not worth funding. If we were menaced by invaders from Alpha Centauri, I might change my mind.