Aerospace startup Hermeus Corp. today announced that it has raised $350 million in equity and debt funding.

The bulk of the sum was provided in the form of a $200 million Series C round led by Khosla Ventures. The deal, which also included contributions from more than a half-dozen other backers, valued Hermeus at $1 billion. A group of institutional lenders provided the remaining $150 million.

Los Angeles-based Hermeus is developing drones for the U.S. military. The company says that its aircraft will be hypersonic, which means they will fly five times faster than the speed of sound. Hermes plans to achieve such speeds with a jet engine that uses a so-called turbine-based combined cycle design.

Jet engines vary significantly in their construction, but they all operate on the same basic principle. They take in air from the atmosphere, compress it and heat it by burning jet fuel. The compressed air is then moved toward the engine’s exhaust, where it’s allowed to expand. This air expansion produces the thrust that enables aircraft to fly.

Hermeus’ turbine-based combined cycle engine incorporates elements from two existing jet engine designs: the turbojet and the ramjet. A turbojet uses heavy spinning blades to compress the air that it takes in, while a ramjet doesn’t have any large moving parts. The latter design is more suitable for use at speeds exceeding Mach 3, or 2,300 miles per hour.

Hermeus’ engine operates like a turbojet during takeoff and switches to ramjet mode after passing a certain speed threshold. That speed is the reason a ramjet doesn’t have any moving parts. Air hits the engine so fast that it’s compressed on its own, which removes the need for the spinning compression blades used by turbojets.

Hermeus’ engine is based on a modified version of a more than 50-year-old engine design called the Pratt & Whitney F100. RTX Corp., the defense contractor that makes the latter system, invested in the startup’s funding round through its venture capital arm. Hermeus’ engine also incorporates a so-called precooler that lowers the temperature of the incoming air to boost aircraft speed. 

The company completed its first test flight last May with a subsonic demonstrator aircraft. A few weeks ago, it flew a new iteration of the aircraft that is nearly three times larger and four times heavier. Hermeus’ next goal is to achieve supersonic speeds.

“This new funding lets us build multiple aircraft at the same time and scale our manufacturing capabilities, adding more hardware richness and robustness to our program,” said Hermeus founder and Chief Executive Officer AJ Piplica. “That accelerates our path to ramjet-powered flight.”

Photo: Hermeus