While the world's biggest space powers - the US, Russia and China - have put military and intelligence assets in orbit since the 1960s, they have done so mostly in secrecy.

Major stock indexes and the dollar fell on Wednesday as investors worried about a deteriorating U.S. fiscal outlook and Treasury yields climbed following a poorly received sale of 20-year U.S. bonds.

U.S. stocks fell on Wednesday as Treasury yields rose and investors digested prospects that passage of U.S. President Donald Trump's proposed tax-cut bill could swell the federal debt.