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.

Days after successfully flying its Quarterhorse unmanned aircraft at supersonic speeds, an industry-first defense aviation company, Hermeus, has received the largest-ever contract awarded by the Defense Innovation Unit (DIU) to demonstrate high-Mach flight combined with high-Mach payload release.

The new $ 159 million award, which increases the original contract to a total of $219 million, will allow Hermeus’ engineers to expand on previous high-Mach test flight milestones in direct partnership with the U.S. Air Force and the U.S. Navy, with the goal of providing the American warfighter with the most advanced arsenal capable of delivering munitions and payloads around the world at record-setting speeds.

“By delivering flight-ready aircraft and demonstrating payload release at speed, we will prove this technology can create a decisive military advantage on a timeline that matters,” explained Hermeus CEO and co-founder, AJ Piplica. “Our focus is on providing the Air Force and Navy with the validated data they need to transition these platforms into the future force.”

High Mach Payload Release: “A Game Changing Warfighting Capability”

When announcing the new DIU award, Hermeus executives noted that the program will include a series of “intensive flight tests.” The first is expected later this year, while the final flights are expected sometime in 2027.

Although few specifics were provided, the company said the flights will “prove the aircraft can maintain high speeds and expand its performance limits” while also demonstrating the successful carry and release of payloads at high velocity. The company also noted that all flight data gathered during the development and testing phases “will directly inform service experimentation and future acquisition decisions.”

Although the U.S. Military has several aircraft capable of exceeding the speed of sound, and several more hypersonic (exceeding five times the speed of sound) aircraft and missile prototypes, delivering payloads from high-Mach aircraft has remained a challenge. However, some military experts argue that the U.S. would benefit greatly from the capability.

When discussing the need for high-speed payload release, DIU Military Deputy Major General Joe “Solo” Kunkel said that the largest problems the military is facing in the future are “generally around time and distance,” and the associated challenges with getting to distant locations “in a timeframe that matters.”

“I care about the warfighting capability, providing advantage to our partners and us in the fight, and making sure that we can walk into every fight with swagger,” General Kunkel said, adding that mass producing the technology developed by Hermeus could move it from a test platform to a “game-changing warfighting capability.”

“I think we found a significant number of use cases where it can be used as a weapon,” the General added. 

Moving High-Mach Capability Out of the Lab

When discussing the company’s approach that convinced the DIU to offer its largest award in the organization’s history, including what they describe as “reclaiming the lost art of rapid iterative prototyping to build the fastest aircraft in the world today,” Hermeus noted that directly partnering with the USAF and USN allows their engineers to align tests with future mission needs and shorten the path from testing to deployment.

“By prioritizing relentless hardware iteration, we deliver high-speed systems at the pace of the modern battlefield,” the company’s statement explained. “We work with the Department of War to provide the high-speed capabilities our nation and its allies need to maintain a durable, asymmetric advantage.”

When discussing the significance of the upcoming tests and the overall need for high-Mach flight payload deployment, including the benefit of the performance data, the company CEO heralded the DIU’s award, noting that the financing will help them move their successful demonstrations into real-world high-Mach platforms.

“This program is about moving high-Mach capability out of the lab and into an operationally relevant environment,” Piplica said. 

Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.