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President Donald Trump is expected to sign a new policy directive Tuesday laying out his administration’s long-awaited plans for establishing a Space Force.

“This afternoon the President is going to sign the Space Directive, Policy Directive that will establish the Space Force and give presidential direction to establish the Space Force within the Department of the Air Force,” Gen. David Goldfein, the chief of staff of the Air Force, told an audience Tuesday at the Brookings Institution in Washington.

Defense officials tell CNN that following Trump’s signing of the directive, the administration will then submit a legislative proposal to Congress, seeking the necessary authority and funds to establish the new military service.

However, given Democrats control the House, congressional support for the initiative is not guaranteed.

The cost of the Space Force has been debated, with the Air Force initially estimating a cost of $13 billion being significantly higher than the estimates touted by Acting Secretary of Defense Patrick Shanahan, who has said it would be less than $5 billion.

CNN has previously reported that the Space Force would fall under the Department of the Air Force, making it akin to the US Marine Corps’ relationship to the Department of the Navy.

The decision to put the Space Force under Air Force control represents a win for the department, which was known to be resistant to the establishment of a completely separate service due to the fact that the vast majority of personnel that would go to a potential Space Force would be taken from the Air Force.

Goldfein said that “80 to 90%” of space-focused military personnel are currently in the Air Force.

In June, Trump appeared to call for the Space Force to be separate. “We are going to have the Air Force and we are going to have the Space Force — separate but equal,” he said then.

While Trump had made it clear he had sought a separate and independent service, Goldfein said a wide range of options were considered.

“The President laid out his direction, and we were looking at a number of options, everything from a separate department, separate secretary, separate service, all the way down to perhaps the left bookend which would be more of a medical corps, JAG corps kind of a model,” Goldfein explained.

“We’ve been in a robust debate, as you’d imagine,” he added.

And while Tuesday’s directive will highlight the administration’s plans for a Space Force, Goldfein acknowledged that a lot of decisions still had to be made to bring it into being.

“There’s a thousand now decisions that have to be made to be able to work through the intricate details of how we move forward in establishing the service within the Department of the Air Force,” he said.

Goldfein said that from his perspective, the most critical aspect that needed to be established first was a US Space Command, something Trump had previously directed in December.

The US Defense Intelligence Agency recently released a report saying that Russia and China were boosting their space capabilities and developing weapons systems capable of striking US satellites.

“We’re the best in the world in space and our adversaries know it, they’ve been studying us and they’ve been investing in ways to take away that capability in crisis or conflict. That, to me, is the problem statement and we as a nation cannot let that happen,” Goldfein said.