Google co-founder Sergey Brin is secretly building his own giant airship inside a NASA hangar, Bloomberg reports today. The craft — which apparently looks like a classic zeppelin — is housed at NASA’s Ames research facility, the publication’s sources say, but it’s not clear whether the airship a prototype for a business venture, or just a passion project for the billionaire.

According to Bloomberg’s sources, Brin’s dirigible is not yet complete, but engineers have already built a metal frame that takes up much of the hangar. Google’s Planetary Ventures division gained access to the Ames facility in 2015, and started using its vast hangars as labs and test areas for new technologies, but the sources note that the airship isn’t a proper Alphabet project.

Brin has been fascinated by airships for a long time, the sources claim, but was inspired to build his own after seeing pictures of the USS Macon — an airship built in the 1930s by the US Navy, and also once housed at the Ames facility. Once the location was secured, and the concept imagined, he assigned Alan Weston — who previously headed NASA’s Ames programs — to lead the project.

The craft’s metal skeleton is reportedly complete

In an age of flying taxis, internet-beaming drones, and self-driving cars, airships might sound a little outdated, but Weston has spoken before about the potential of the vehicles to carry freight at reduced cost. In a 2013 radio interview, he described a helium-filled airship that used a system of “breathing” that would allow it to carry 500 tons of cargo, while remaining “more fuel-efficient than a truck.” Weston — who reportedly performed one of the world’s first bungee jumps — also noted that airships could drop goods off where they were needed, rather than dumping them at ports or airports, necessitating further travel by road or rail.

Weston didn’t respond to Bloomberg’s request for comment, while Brin himself said he “[didn’t] have anything to say about this topic right now.” That statement could be the Google co-founder being cagey and obfuscating his company’s plans to get into the airship business, or it could simply be the sentiment of a man who just really likes blimps. After all, what good is it being a billionaire if you can’t secretly build your own giant airship in a repurposed NASA hangar?