There are many things that have such a long payout period, that private enterprise will never touch it. The first government sponsored program along this line was the transcontinental railroad, which made a single nation out of two sea coast cultures. This country wouldn't be the same had we not done that.
That being said, I think there are better ways to get into space without NASA. The loan guarantees of the transcontinental railroad, plus land (previously worthless, being without a railroad) did the trick in the 1870's. Both industry and government made money.
The same should be done again. Offer loan guarantees and land on the moon/mars.