The silhouette of a U.S. Army Apache helicopter is seen against the moon.

"The myriad of details which people joke about, the academies, the uniforms and what not, those may seem trivial but they are details that need to be worked out," James said raising concerns that the proposed space force will be buried in bureaucratic minutiae.

"I do not believe we should have a separate space force," she added noting that the potential sixth service will be a distraction to pressing U.S. national security matters.

"It is a virtual certainty that it [a space force] will be a huge undertaking that will consume a lot of time, effort, thinking," Deborah Lee James, 23rd secretary of the Air Force and principal defense space advisor for the Obama administration, said at the Brookings Institution on Monday.

As the Pentagon works to fulfill President Donald Trump 's desire to create a sixth service branch, a former secretary of the Air Force warned that a "space force" would worsen problems plaguing the U.S. military's space efforts.

What's more, James also explained that the formation of a sixth military branch will "zap resources away that could otherwise go to capabilities."

In lieu of Trump's proposed space force, James recommended that the president consider the establishment of a new functional combatant command similar to U.S. Strategic Command that would be solely focused on space.

James shared that the Pentagon's top brass is also hesitant to form a new military branch. "None of them are in favor of a space force but they are stuck," she said. "The president has said it and it will be interesting to see how they now deal with it."

Read more: What Trump's 'Space Force' might look like – and when it would be ready

When asked how expensive a new service branch will cost, James noted that it is certainly something that cannot be properly established without a significant investment.

"I do not know how much it would cost to set up a separate military service but if anyone thinks you're going to do it on the cheap I will tell you that I've never seen anything like this done on the cheap. So, No. 1, it will cost more than what they predict," James said.

Trump's sprint to develop a space force became apparent during an emphatic June 18 speech to the National Space Council. He announced his wish for the Pentagon to create a new sister service branch to stand alongside the Army, Air Force, Navy and Marine Corps.

"I am hereby directing the Department of Defense and Pentagon to immediately begin the process necessary to establish a space force as the sixth branch of the armed forces," Trump said before asking Marine Corps Gen. Joseph Dunford, chairman of the Joint Chiefs, to see the directive through.

"Our destiny beyond the Earth is not only a matter of national identity but a matter of national security," Trump said.