We could've cured cancer, gone the Mars, developed hypersonic flight, and probably about a dozen other projects that would have had a huge impact. The interest alone is 10x bigger than NASA's budget.
In general, the foreign debt taken on by the US is similar - e.g. bonds issued by various countries, and bought by the citizens and the government as an investment asset.
Finally, the better you get at repairing cancers the more cancers you will be repairing because as we age our cells copying mechanisms age as well and that's one possible source of cancer. So cure one cancer, cause the organism to live longer and deal with a whole bunch more.
Cancer is to some degree systemic, it is a side effect of the way our bodies work. I'm holding out for a cure or even a vaccin for HIV/Aids but I'm skeptical on a 'cure for cancer', even though having such a thing would obviously be good.
We get deficits via a lot of $6.3M/yr expenditures.
...and rising, and falling, and rising, etc. Short-term movement depends on the economy and on the year of Presidential tenure (i.e. expect more spending in year one than year seven). The total over any decade is unlikely to be a surplus.
Kind of... To begin with, science jobs pay poorly, and a lot of exceptionally intelligent people choose high paying but ultimately ~zero-sum jobs like law and investment banking. And then there is the continual struggle for funding, which absorbs a good part of the scientists' time and energy.
These discussions often ignore that we have done very, very well for certain cancers.
Compare this to EBola, which, even liberal estimates suggest we won't see more than 100 fatalities/year in the United States, and America has invested $1Billion.
Cancer is a multi-trillion dollar problem - but the technology required to effectively combat it (nanobots, protein folding technology, targeted molecules, rapid-dynamic DNA assessment) is still many decades in the future.
Of course, doing the basic research to develop those technologies is going to cost a lot of money as well. But the difference is, unlike many human maladies (Old Age) Cancer has a pretty well defined solution, we (perhaps appropriately) just haven't invested enough time and resources to deliver that solution yet.