We can build an Orbital Ring Space Elevator today, using steel and kevlar. The Orbital Ring goes to low earth orbit, so it does not need advanced materials.
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Why build the Orbital Ring? It would cut our costs of going to orbit from about $2000/kg to about $1/kg. There are individual asteroids that have tens of trillions of dollars in materials on them that could be mined. One mission could easily pay for the cost of building the Orbital Ring.
We could then deploy solar power satellites in orbit above cloud cover and return the power back to the surface with near zero loss by running power transmission cables down the elevator, and sell the power at a profit.
With increased luminosity in space, enhanced exposure time, and the ability to deliver base loads, solar panels pay for themselves in only 1-2 years while having a 20 year life time.
In other words, if you put $5 trillion of solar panels into space, you get your $5 trillion back by the end of year two and a $5 trillion income stream each year thereafter.
In other words, the US could cut everyone's taxes, both personal and business, income, capital, death, or otherwise, all to 0%, not even cut any benefits or current spending, and pay off the national debt within a decade.