WASHINGTON – The Space Force moved closer to liftoff Tuesday after President Donald Trump signed a directive to create another branch of the military whose mission would be to monitor the heavens and protect the USA from attack.

During a signing ceremony in the Oval Office, Trump said he views the new military branch as part of his responsibility to protect the nation.

"I was put here for security, whether it's Space Force, which I'm doing today, or whether it's borders," the president said.

Money for the program will be included in the administration's proposed budget for 2020 that will come out next month, the White House said Tuesday morning. That seed money is likely to be less than $100 million.

Eventually, an undersecretary of defense for space would be named, and the program – which would start as a division of the U.S. Air Force – would become the sixth armed service, joining the Air Force, Army, Marine Corps, Navy and Coast Guard.

The idea of a military force patrolling Earth's orbit was dismissed not that long ago by critics as far-fetched and wasteful. Space Force became the object of ridicule on the internet and among late-night comics.

Still, Trump has enthusiastically pitched the idea, tweeting in August, "Space Force all the way!"

The idea has been a harder sell in Congress, where concerns about cost and redundancy stymied efforts to create another military branch.

The Air Force, which oversees the Space Command, also initially resisted the branch, saying it was unnecessary and bureaucratic. In September, a memo from Air Force Secretary Heather Wilson placed the five-year cost of establishing the new branch at about $13 billion.

The White House expects the cost to be far less. The Pentagon would consolidate functions "to minimize duplication of effort and eliminate bureaucratic inefficiencies," Trump's directive says.

The branch would include uniformed and civilian workers supporting space operations for the military, the White House said.

The creation of a Space Force would happen over several phases and could take years to complete. But Florida Gov. Ron DeSantis, a political ally of Trump, wasted little time in trying to capitalize on the announcement.

"Today, I am formally sending a request to @realDonaldTrump to place the headquarters for the Space Force Combatant Command here in Florida @NASAKennedy in Cape Canaveral," DeSantis tweeted. "This is part of Florida's history and is a logical fit for our state."

Sen. Marco Rubio, R-Fla., made a similar pitch in December.

The administration is doing what it can now without approval from Congress, which remains divided on the idea. Lawmakers ultimately will determine the fate of the proposed force, because they must decide whether to authorize the creation of a military branch and whether to approve money for the plan.

"We will recognize that space is a new war-fighting domain with the Space Force leading the way," Trump said in January during a speech at the Pentagon.

The president said he hoped the United States would never have to use space weapons, but there are "some very bad players out there. And we're a good player – but we can be far worse than anybody, if need be."

Related:Countdown to Space Force continues as Trump administration details trajectory of plan

Related:'The ultimate adventure': Virgin Galactic's space tourism plan demands courage and $250K

Former NASA Administrator Sean O'Keefe said starting a new military branch is a bad idea.

"The ‘Space Force’ as a separate military service entity would still compete with all the other defense-related priorities for resources and leadership attention," said O'Keefe, a professor at Syracuse University’s Maxwell School of Citizenship and Public Affairs. "There’s no reason to believe that space-related programs would fare any better than they do today under the U.S. Air Force recognizance."

At a meeting of the National Space Council in October, Vice President Mike Pence laid out milestones needed to establish what would be the nation's first new armed service since 1947. Those steps include:

Establishing a chain-of-command structure that would govern day-to-day operations and ensure integration with other branches.

Drawing up rules of engagement that detail the circumstances for enemy combat not only in Earth's orbit where U.S. military and commercial satellites circle the globe but also on the moon, where NASA plans a return by the end of the 2020s.

Working with lawmakers who have ultimate say on the design and funding of a Space Force. Defense authorization bills have not included the go-ahead from Congress to create a force, so the challenge will be to convince Capitol Hill such a step is needed for the nation's security.

The council endorsed directives that Trump signed calling for a return to the moon, promoting more commercial activities in space and managing traffic in low-Earth orbit.

Contributing: David Jackson