HOUSTON SPACEPORT—On a cloudy day in late March, Andrew Duggleby guided me a safe distance away from a rocket engine. We did not have to go far, maybe 50 meters, because the prototype engine designed and built by his small engineering team is not that large.

We waited for a few minutes before steam began to hiss out of the engine. And then, for a few seconds, the engine emitted a distinctive whistling sound. “There it is!” Duggleby exclaimed. By it, he meant the sound of a rotating detonation engine firing after its ignition. The sound indicated that a reaction was successfully rotating at 20,000 times a second around the engine.

Duggleby is chief technology officer of a company he co-founded with his wife, Sassie. Venus Aerospace has the goal of building a hypersonic aircraft that can carry perhaps a dozen passengers and travel at the astonishingly fast speed of Mach 9, or more than 11,000 kilometers an hour.