Under SpaceX CEO Elon Musk's vision, humans could then land on the Red Planet in 2029, though he admitted 2031 is "more likely."

Planning for a war with China has dominated Pentagon thinking for decades, well before a possible confrontation with Beijing became more conventional wisdom on Capitol Hill. The United States has built its Air Forces, Navy and Space Forces — and even more recently its Marines and Army forces — with a possible fight against China in mind.

Billionaire Elon Musk arrived at the Pentagon on Friday morning for expected meetings with senior U.S. military leaders as the close ally of President Donald Trump makes sweeping cuts to the U.S. government.

Elon Musk and his companies, including Tesla and SpaceX, have been facing attacks from the left since the billionaire took on a role within President Donald Trump's administration to cut government spending.