You may have heard about President Trump's plans to build a space force, what would be a sixth branch of the U.S. military... Now we're starting to find out just how much that will cost.

FOX's Jim MacKay explains:

$12.9 billion: That's the estimate for the first five years of the planned Space Force, according to some number crunching by the Air Force.

The Air Force five-year cost estimate came out of a memo from Air Force secretary Heather Wilson, who has proposed the Pentagon ask Congress for the authority and cash, to build a Space Force headquarters as early as 2020.

All of these plans would need to get the okay by Congress and the administration right now is planning to propose legislation authorizing the establishment of the Space Force in early 2019.

Jim MacKay, FOX News.

Follow Jim MacKay on Twitter: @JimMacKayOnAir