I'm afraid that I must disagree with the Perfesser. He remarks that:
A basic tenet of libertarian welfare economics is that government should provide only those services that will be underproduced due to market failures. The government provides national defense, for example, because security is a public good and therefore will be underproduced by the private sector. I don't think you can make the case anymore that space travel is a public good:
Public goods ... are non-excludable and [non-rivalous] in consumption. An example is a street sign. It will not wear out, even if large numbers of people are looking at it; and it would be extremely difficult, costly and highly inefficient to limit its use to only one or a few persons and try to prevent others from looking at it, too. A traffic light or clean air is a further example.
Space travel obviously satisfies neither condition: You can restrict access to your spaceship and not everyone can use it simultaneously.
"Leave Space to the Private Sector" (17 Jan 04) (citation omitted). This, I am afraid, misunderstands the nature of space travel: it considers the spaceship to be the entire program.
One simple example of this is a look at something similar: aircraft development. It wasn't just the aircraft themselves. Sure, we can fly higher and farther. But the computer on your desk (or lap) has benefitted from materials initially developed for aircraft. Roads and other construction have benefitted from developing the technology to lay down a two-mile-long, perfectly flat runway. Portability of radios, high-compression internal combustion engines, digital control systems in factories, and more other things than I can shake a stick at have been at least catalyzed by aircraft development. Yet, on a strictly accounting basis, those things would not be ascribed to aircraft development. And, of course, none of this was predictable just from the idea that "we need better aircraft."