The real issue with NASA is that they are subject to internal politics. This includes the ever critical matter of funding. Right now NASA can call upon something like 0.5% of the US federal budget, and at 3.9 trillion dollars that's about 20 billion dollars, accounting for the rounding error.
During the heydays of the Space Race NASA could call upon 2 to 4% of the US's federal budget, and at the time the USA's federal taxes were pretty high. I think it boiled down to something like 2 percent or more of the USA's GDP at its height. I mean, the current GDP of the USA is 18 trillion 624 billion dollar and change (calculated for 2016 according to tradingeconomics.com), which would mean that if NASA could call upon the same resources now as it could then it'd have a budget of 372 billion dollars and change.
I mean, think for a moment; NASA has in comparison to when it was actually doing the whole sending people to the Moon thing an 18 times smaller budget than then. And that's the conservative estimate not accounting for shifts in the economy. And it has a lot of resources tied down in maintaining what it already has.
During the heydays of the Space Race NASA could call upon 2 to 4% of the US's federal budget, and at the time the USA's federal taxes were pretty high. I think it boiled down to something like 2 percent or more of the USA's GDP at its height. I mean, the current GDP of the USA is 18 trillion 624 billion dollar and change (calculated for 2016 according to tradingeconomics.com), which would mean that if NASA could call upon the same resources now as it could then it'd have a budget of 372 billion dollars and change.
I mean, think for a moment; NASA has in comparison to when it was actually doing the whole sending people to the Moon thing an 18 times smaller budget than then. And that's the conservative estimate not accounting for shifts in the economy. And it has a lot of resources tied down in maintaining what it already has.