FILE PHOTO: NASA Administrator Jim Bridenstine (L) chats with US Strategic Command Commander Gen. John Hyten as they wait for the start of the House Armed Services Strategic Forces Subcommittee's joint hearing with the House Science, Space and Technology Committee, in Washington, U.S., June 22, 2018. The panel heard testimony on President Donald Trump's proposed Space Force. REUTERS/Mike Theiler/File Photo

WASHINGTON (Reuters) - The proposed U.S. Space Force, a new military service backed by President Donald Trump, could have an initial budget of less than $5 billion, the deputy defense secretary said on Thursday.

The U.S. Air Force estimated start up costs for a proposed U.S. Space Force will be around $13 billion in the first five years.

The Air Force is the U.S. military branch that currently has responsibility for space.