The focus of the closed-door get together was "innovation," according to a Defense Department spokesman, although Musk is also looking to win more government business for SpaceX, which launches satellites into orbit.

Neither Carter nor Musk spoke to reporters after their meeting, but Defense Department spokesman Peter Cook said Monday that Carter "has been reaching out to a number of members of the technology community to get their ideas, their feedback, find out what's going on in the world of innovation."

When asked by CNN's Barbara Starr if Musk's role as a defense contractor would complicate the meeting with Carter, Cook said: "The secretary knows very well the rules and regulations required, and how to keep those issues separate and apart and transparent."

Carter has focused intensely on promoting links between the Department and technology companies from the private sector, making a number of trips to Silicon Valley and establishing the Defense Innovation Unit Experimental (DIUX) in Silicon Valley and Boston.