President Trump is pushing forward to launch a space force as a new branch of the military – but it would at first be under the umbrella of the Air Force. The proposal requires an act of Congress.

This represents at least a temporary shift –Trump had stated that he wanted a space force that is "separate but equal" from the Air Force.

A space force is an often-repeated goal of the administration, announced by Trump last June as a sixth branch of the armed forces to ensure "American dominance in space."

Critics of the plan have suggested that it could further complicate military bureaucracy at great financial cost. The White House says it would mitigate threats in space from other nations.

"Potential adversaries are now advancing their space capabilities and actively developing ways to attack and destroy our use of space in a crisis or conflict," a senior administration official said, as NPR's Scott Horsley reported.

On Tuesday afternoon, Trump is expected to sign a policy directive that will request the secretary of defense to draft legislation to establish a separate "Space Force" branch of the U.S. military.

The new force's chief of staff would be a member of the Joint Chiefs of Staff and would be overseen by a civilian Air Force under secretary for space.

It would be akin to the structure of the Marine Corps, which is a part of the U.S. Department of the Navy but with separate representation on the Joint Chiefs.

The senior administration official said that if the plan is approved by Congress, the space force could eventually fully separate from the Air Force, as Horsley reported.

The "force would consolidate command of the military's existing satellite systems into a single command. Those include reconnaissance satellites, GPS, missile-warning systems and communications platforms," as NPR's Geoff Brumfiel reported last year.

Todd Harrison, director of the Aerospace Security Project at the Center for Strategic and International Studies, told Brumfiel that the space force would not actually involve troops in space.

"There's no space marines; there's no people flying around with jetpacks," Harrison says. In an opinion piece for Breaking Defense, he recently argued that a space force is "needed to consolidate authority and responsibility for national security space in a single chain of command."

The Air Force is currently responsible for many of the U.S. space-related activities. Last September, Air Force Secretary Heather Wilson said in a memo that establishing a space force would cost some $13 billion over a five year period.

"The costs here are additive costs," she told Defense News. "They are not just the movement of other capabilities and consolidate them. To stand up a department that's responsible for recruiting and training and planning and programming and budgeting and all of the leadership requirements that a department has, it's a major undertaking. It's a bold idea."

If the legislation passes, it would be the first time Congress approved a new branch of the military since 1947, when it created the Air Force.

As Horsley reported, administration officials on Tuesday did not clarify the cost of a future force. They did say establishing a new headquarters would cost less than $100 million. "Other money would come from consolidating existing space functions within the space force," Horsley added. "The president's budget might also propose additional money to cover the cost of enhanced military space functions."

And while the idea of a space force is a crowd-pleaser at Trump's rallies, it has been met with skepticism or even ridicule among other audiences. The Washington Post rounded up cartoons from around the country about the idea.

And, Netflix has announced that Steve Carell is going to star in a new comedy series about the idea. It's a "Workplace comedy centered around the people tasked with creating a sixth branch of the armed services... Space Force."

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