“You could fly some sort of a weapon around the moon and it comes back — it could literally come at [objects] in GEO…and we would never know because there is nothing watching in that direction,” he said. “Why do you need a relay satellite flying around L2? So you can communicate with something that’s going to land on the other side of the moon — or so you can fly around the other side of the moon? And what would that mean for our assets at GEO?”

Michael Griffin, defense undersecretary for research and engineering, has been pushing for a more robust response to threats against U.S. assets in space. It’s one reason he and others want to move away from big, easily targetable satellites in GEO toward large constellations of small, cheap ones in low-earth orbit.

“China and Russia now have the capability to go after” intelligence and communications satellites in GEO, Griffin told reporters in August. “Those assets are what we use for communication and reconnaissance and missile warning and position, timing and navigation, a whole bunch of features that we use for war fighting.”

Gossel said that the actual threat from lunar satellites like the Chang’e 4 is very small — but that it’s his job to be a bit “paranoid” and seriously think about even highly unlikely threat scenarios.

Brian Weeden, who directs program planning at the Secure World Foundation, argued that the possibility was too low to constitute a significant threat. “I think speculating about military applications for China's lunar program is akin to Soviet concerns about the Space Shuttle being a potential weapon,” Weeden said. “There is a grain of truth behind the Shuttle being a space weapon and the Chinese lunar program having possible military applications. Doesn't mean either is reality, though.”

Still, Gossel said, the national-security community’s interest in China’s lunar activities is “building steam.” Stephen Kitay, deputy assistant defense secretary for space policy, as well as the office of the Director of National Intelligence have "an interest in it,” he said. “That’s where I come into play.”

Paulina Glass contributed to this post.