U.S. Defense Secretary James Mattis (R) introduces Vice President Mike Pence before he announces the Trump Administration's plan to establish the U.S. Space Force by 2020 at the Pentagon, Virginia, the United States on Aug. 9, 2018. U.S. Vice President Mike Pence said Thursday that the United States plans to establish a Space Force by 2020, an idea floated by President Donald Trump and questioned by many top officers at the Pentagon. (Xinhua/Ting Shen)