Defense aviation company Hermeus has announced the development of Ramjet-X, its next-generation ramjet propulsion test vehicle capable of carrying test payloads to high Mach speeds.
The company said Ramjet-X, designed to launch mid-flight from a carrier aircraft, offers the key advantages of competitive high-Mach test platforms while keeping costs low enough for a wider range of mission profiles.
Pre-flight testing of Ramjet-X is already underway, with its first official prototype test flights expected in 2027.
Ramjet-X Will Launch Mid-Flight from Quarterhorse
Most conventional jet engines can’t achieve supersonic speeds without dumping raw fuel into an afterburner and literally rocketing past the sound barrier. To travel at high Mach speeds without relying on rocket-style propulsion, engineers have turned to ramjet engines.
While ramjets are effective, they rely on the high-speed influx of air to operate. This limitation means aircraft equipped with this type of propulsion must be propelled to higher speeds by another craft or booster rocket before they can engage.
In an email to The Debrief, a Hermeus spokesperson explained that current options often rely on “large and expensive” boosters that are discarded after each test. Conversely, Ramjet-X relies on the company’s reusable aircraft to reach launch velocity.
“Ramjet-X is designed to be carried by Quarterhorse, which provides the speed and altitude required for deployment,” the company told The Debrief.
The company could not disclose what speed Quarterhorse must achieve before it can launch Ramjet-X. However, the spokesperson did note that the launch craft is designed to return to home base for future missions.
When asked about Ramjet-X’s specific operating velocity once it disengages from Quarterhorse and engages its ramjet propulsion system, the company could only say the vehicle will operate at “High-Mach speeds.”
Conventional ramjets use a combination of high-velocity air and fuel to achieve extreme velocities. Hermeus said they cannot disclose specifics about Rocket-X’s fuel requirements.
Mission Profiles and Repeatable Architecture
Because of the sensitive nature of potential future missions, Hermeus was cautious about sharing specifics of any planned missions. The company also couldn’t provide technical details on what a typical mission profile might look like.
However, a Hermeus spokesperson told The Debrief, the vehicle’s architecture “allows customers and partners to integrate payloads, sensors, communications and computer systems, autonomy, material samples, propulsion technologies, and other experimental hardware and software onto Ramjet-X for testing in representative sustained high-Mach conditions.”
Hermeus also highlighted the potential cost savings of a “repeatable platform, launch architecture, and flight-test infrastructure,” designed to dramatically lower costs without sacrificing versatility or reliability.
“Instead of relying on a large dedicated expendable booster to accelerate the test vehicle into its ramjet operating regime, the launch aircraft provides much of that energy and then returns to fly again,” the company told The Debrief. “This architecture allows Hermeus to fly more by reducing the cost of expendable launch hardware.”
“High-speed flight testing is extremely expensive, and you don’t get many shots at it,” Hermeus CEO Zach Shore explained.
“Another Order of Magnitude Reduction”
Hermeus said specific unit costs are not currently available. However, they said a projected cost per minute of high-Mach test time “is in the low $100k’s per minute.” For comparison, the company highlighted the historic and current costs of high-Mach flight testing.
“Most of the below comparisons are rocket-based but will give you an idea how costly high-Mach tests are and why Ramjet-X will fundamentally change the equation,” Hermeus told The Debrief.
Older examples include NASA’s X-43, which achieved around 21 seconds of high-Mach flight, and the Air Force’s X-51, which achieved around 350 seconds. Hermeus said both multi-year efforts cost around $450 million each in today’s dollars.
Current options include rocket-powered test flights aboard Rocket Lab’s HASTE, which Hermeus said run $10-20 million each, “not including the expendable cruise or glide vehicles.” The company also pointed to Stratolaunch Talon-A missions.
“Even though fully reusable, (they) are $10-12m per flight for a few min of on-condition time,” the company told The Debrief.
Conversely, Hermeus said its current projections of less than a million per minute offer potential customers “another order of magnitude reduction in the problem that matters most.”
“Ramjet-X is being designed around simplified manufacturing, rapid production, and expendability in meaningful quantities rather than the traditional model of building a small number of highly bespoke high-speed test articles as was done in other high-speed airbreathing flight test programs like X-43 and X-51,” the company told The Debrief.
Development of Ramjet-X is already well underway
When detailing the newly announced Ramjet-X’s benefits, Shore noted that their system gives them a way to place new systems into sustained high-Mach environments “without building an expensive one-off test program every time.”
“Bringing speed, sustained flight, and scalability all into one system lowers the barriers to gathering extremely valuable data from these conditions and accelerates programs for both us and our customers,” the Hermeus CEO explained.
When announcing Ramjet-X, Hermeus said the vehicle’s ramjet engine is already undergoing extensive testing at its Florida-based HEAT facility. Future tests will occur at the company’s California headquarters, with the first flight tests planned for 2027.
Christopher Plain has spent the last six years as Associate News Editor and Head Science Reporter at The Debrief. Follow and connect with him on X, learn about his novels at plainfiction.com, or email him at christopher@thedebrief.org.