While the Chinese economy is quickly growing the US is still many times larger. The last projections I saw show China pulling even in the 2030-2040 timeframe and pulling slightly ahead in 2040-2050. And that projection postulated a growth rate for China that would be hard to maintain for 40 years.
The last figure I saw said 2020, but that was before the current financial crisis. A major collapse in the financial services industries will lead to even bigger trade deficits for the USA.
They are huge already - just not as big as the USA yet. However the USA is consuming far more than it exports, it's trade deficits are massive and it cannot sustain that situation forever in the light of mounting competition from the new would-be superpowers of China and India. The massive pool of cheap labour gives China an advantage the US won't have even if you let the entire population of Mexico in.With all news stories about China growing people assume they are huge already; they are not. Just like people assume China manufactures most of the stuff in world already when that honor still belongs to the USA.
Don't get me wrong - the USA is not going to end up a provincial power in twenty years, or turn into Britain or France. It will remain a massive economic and military power throughout most of the next century.
BUT - to wrench this back on topic - the USA cannot and will not afford to spend as much on a space program as the Chinese going forwards. Quite simply with the economic crisis, the constant financial drain of two wars and a simple lack of political will there is not a cat in hell's chance of NASA getting even a fraction of the money it needs.
All it takes is the political will. We are about to spend 700 billion dollars we don't have because we have the political will to do it. If China makes great strides in space we will have incentive and political will to compete with them.