Reasons for Elon Musk's trip to the Pentagon (not including fan theories that he's Iron Man)

When billionaire entrepreneur Elon Musk and United States Secretary of Defense Ash Carter sat down together at the Pentagon on Wednesday, they probably had a lot to talk about.

From SpaceX's particular brand of rocketry to Tesla Motors' disruption of the car industry, Carter and the sprawling department he heads have a lot to learn from Musk's agile way of working within and outside of an industry.

SEE ALSO: Elon Musk drops more hints that he is, in fact, Iron Man

However, the exact topic of the meeting have not been revealed, leading to much speculation as to what, specifically, they talked about.

Is Musk — as he joked — actually building an Iron Man suit? Does the Defense Department want to award them more launch contracts? Are Secretary Carter and Musk both just really big fans of video games?

According to comments by Pentagon Press Secretary John Cook ahead of the meeting, Carter and Musk met at the Pentagon to chat about "innovation."

"Obviously, Elon Musk is one of the most innovative minds in this country," Cook said, according to a transcript.

Of course, "innovation" isn't exactly the most specific conversation starter, but Carter is known for his efforts to build bridges between the Pentagon and Silicon Valley.

Carter is a fan of Silicon Valley

Carter is the first Secretary of Defense to even visit Silicon Valley in about 20 years, and this meeting with Musk comes after he met with Facebook COO Sheryl Sandberg and LinkedIn co-founder Reid Hoffman, among other tech industry leaders. 

Meeting with innovators in Silicon Valley can help the Defense Department "stay as ahead as we can from a technological standpoint," a Defense Department official told Mashable in an interview.

Image: DOD/Master Sgt. Adrian Cadiz

Carter explained the agency's Silicon Valley "outpost" during a May speech on innovation in Mountain View, California. 

"When I began my career in physics, most technology of consequence originated in America, and much of that was sponsored by the government, particularly the Department of Defense," he said. 

"Today, we're still major sponsors, much more technology is commercial, and the technology base is global," he said. "And nations like Russia and China are modernizing their militaries to try to close the technology gap with us."

"So, to stay ahead of those challenges and stay the best, I've been pushing the Pentagon to think outside our fix-sided box, and invest aggressively in change and innovation," Carter added.

Image: DOD/Glenn Fawcett

To that end, under Carter, the Defense Department has established the Defense Innovation Unit Experimental (DIUx), set up to help the country stay ahead of the curve on new technologies.

DIUx employs people who came up in Silicon Valley. Isaac Taylor, for example, was the head of operations for Google X before joining the Pentagon outfit.

Musk is a poster-boy for innovation and government influence

Musk and Carter also have a fair bit to talk about when it comes to SpaceX.

Musk's spaceflight company is already in business with the Department of Defense, planning to launch a spy satellite for the National Reconnaissance Office in 2017, according to the space industry publication Space News. 

And, while exact figures aren't available, Musk has claimed that SpaceX's rockets are far cheaper to fly than rockets from other more established launch providers like United Launch Alliance — a joint venture of Boeing and Lockheed Martin.

Musk is also a perfect example of profitable relationships between private companies and government entities. 

SpaceX has been, in some ways, propped up by its contracts with NASA. 

The company won a key contract to fly cargo to the International Space Station for the agency using the spaceflight company's Dragon capsule and Falcon 9 rocket, and now the firm is working toward fulfilling a contract to fly astronauts to the Space Station as soon as next year.

Of course, that kind of symbiotic relationship can become contentious, too. 

In 2015, SpaceX took the U.S. Air Force to court after United Launch Alliance was awarded a launch contract that Musk's company thought should have been open for competition. 

SpaceX eventually settled the suit out of court and won a contract to launch an Air Force GPS satellite in 2018.