Hermeus is developing Ramjet-X, an expendable ramjet-powered vehicle designed to be released in flight from beneath its Quarterhorse uncrewed aircraft.
The company said in its announcement that the vehicle is intended to reduce the cost of high-Mach airbreathing flight testing.
Ramjets produce no thrust from a standing start and conventionally depend on an expendable rocket booster to reach their operating speed. Hermeus said Quarterhorse would instead carry Ramjet-X to the required speed and altitude, release it, and return for further test sorties.
The company is also positioning the vehicle as a commercial offering it calls “high-Mach Flight Test as a Service”. According to the release, customers would be able to integrate payloads, sensors, communications and computing systems, autonomy software, material samples and propulsion technologies onto Ramjet-X for testing in sustained high-Mach conditions.
“High-speed flight testing is extremely expensive, and you don’t get many shots at it,” Hermeus chief executive Zach Shore said in the statement.
Ramjet-X aims to make high-Mach testing cheaper
The release said ramjet engine testing is underway at the Hermeus HEAT facility in Jacksonville, Florida, and that it is developing high-temperature structures at its El Segundo, California, headquarters. Integrated vehicle testing is planned for 2027.
Shore supplied several of those figures in an interview with Axios published on September 9, 2026. He said
In an interview with Axios, Shore said that Ramjet-X measures roughly 6.7 meters (22 feet) long and 2.1 meters (7 feet) across. Separation would occur at about Mach 3, and the vehicle would then climb to about 100,000 feet (approximately 30,500 meters) and cruise near Mach 4 for tens of minutes. A first flight is expected within a year, and a single Quarterhorse should eventually carry two vehicles.
A concept with precedent
The pairing recalls the Lockheed M-21 and D-21 of the 1960s, in which a ramjet-powered reconnaissance drone was carried on the back of a modified A-12.
Quarterhorse Mk 2.1 reached Mach 1.21 on its third flight in May 2026, after the Federal Aviation Administration (FAA) issued a Special Airworthiness Certificate in the Experimental Category for the aircraft.
Hermeus closed a $350 million Series C round in April 2026 and moved its corporate headquarters from Atlanta, Georgia, to El Segundo.