The U.S. Air Force estimated start up costs for a proposed U.S. Space Force, a new military service backed by President Donald Trump, will be around $13 billion in the first five years, according to a Department of Defense memo seen by Reuters.

The Air Force, the U.S. military branch that takes responsibility for space, authored the Sept. 14 memo outlining a proposal for “a lethality focused organization that will field space superiority capabilities.”

The Trump administration in August announced an ambitious plan to usher in the force as the sixth branch of the military by 2020. It would require Congressional approval.

The Pentagon memo was written by Air Force Secretary Heather Wilson, a former Member of Congress from New Mexico.

The memo estimated that creating a Space Force will cost in excess of $3 billion in the first 12 months with an additional $10 billion needed over the following four years. The U.S. Air Force estimated that there could be more than 13,000 people in the new “Department of the Space Force.”