Exosonic, a startup developing supersonic commercial air travel and UAV tech, is winding down after five years of operation.

In an update posted to its website, Exosonic said it was unable to find the traction necessary to continue operations. 

“Although the founders and team still believe in the need/desire for quiet supersonic flight and supersonic drones for the US Department of Defense, without further customer support for either concept, the company cannot sustain the cash needs to make further advancements,” the update says. 

Exosonic was founded in 2019 by Norris Tie, a propulsion engineer who cut his teeth at primes like Northrop Grumman and Lockheed Martin; at the latter company, he reportedly worked on the low-boom X-59 aircraft for NASA. Exosonic joined Y Combinator’s Winter 2020 cohort and went on to raise over $4.5 million from venture investors, including Soma Capital, Psion Capital, and Stellar Solutions. The startup also bagged several small grants from the U.S. Air Force under its Small Business Innovation Research (SBIR) program. 

The company was making progress: It hit a major milestone earlier this year when it flew its first aircraft, a subscale variant of its supersonic UAV called EX-3M Trident, in a test flight in California. It also had two other vehicles under development: a supersonic airliner called Horizon and a larger UAV called Revenant.

When asked about what Exosonic accomplishment he was most proud of, Tie said, “I’m frankly just proud of taking a childhood dream and building a company around it. I’ve been able to learn so much and meet great people along the way. From a company accomplishment standpoint, definitely flying our EX-3M Trident is the one the team is most proud of. We took an original supersonic aircraft design and flew it (albeit subscale and subsonic), but we did that in roughly <2 years with limited capital.”

It sounds like the company was ultimately unable to bridge what’s often referred to in defense tech as “the valley of death” — the period between R&D and commercialization. This is a well-known problem for vendors looking to sell to the Department of Defense, and a place where venture capitalists have said they could step in — unless they don’t. As Exosonic put it on LinkedIn, “Without further government support for its near-term supersonic UAV development, Exosonic can no longer sustain the capital required to further advance the concept.” 

Tie confirmed that the company has received some interest for potential IP purchases.

The story has been updated with Tie’s comment.