“What Hermeus is proposing is not without risk. We recognize that,” says Lieutenant Colonel Joshua Burger of the Air Force’s Presidential and Executive Airlift Directorate. Lt.Col. Burger is talking about the hypersonic drone Atlanta-based hypersonic propulsion startup, Hermeus , is building and the USAF’s $60 million dollar investment in it.
Hermeus’ ultimate goal is developing a Mach 5 hypersonic commercial transport capable of carrying 20 passengers from New York to Paris in 90 minutes, compared to the seven and a half hours it typically takes today. The company says it will fly that aircraft in 2029. But first it will work on developing and flying an unmanned, reusable hypersonic drone called “Quarterhorse” for the Air Force.
The development of ultra fast hypersonic (defined as Mach 5, roughly 3,800 mph) weapons and vehicles is a top priority for the USAF, squarely aimed at deterring the hypersonic weapons being developed by China and Russia.
The military’s desire to accelerate fielding hypersonic weapons and vehicles is exemplified by the push to get the Army’s long range hypersonic missile, now called Dark Eagle, operational by 2023. The urgency of such efforts was recently summed up by Rob Strider, deputy director of the Army’s Hypersonic Project Office who said, “You know we’re number three in this race and we’ve got to catch up.”
Unlike a rocket-propelled weapon, Quarterhorse could be a valuable air-breathing hypersonic research and development platform for the Air Force. However, there’s been some mixed messaging on its practical purpose. That likely stems from the funding that underpins it.
The $60 million comes from Air Force Life Cycle Management Center’s Presidential and Executive Airlift Directorate, the Air Force Research Laboratory (AFRL) and private venture capital sources.
The USAF’s press release says its engagement with Hermeus “is part of a larger effort led by the directorate to fuel the burgeoning commercial resurgence of high speed passenger travel, and has been dubbed the ‘Vector Initiative”.
The headline outcome of the investment/Vector Initiative would theoretically be a hypersonic presidential executive transport – a vehicle potentially based on the commercial hypersonic transport that Hermeus aims to launch.
But the Air Force’s interest in Hermeus and Quarterhorse is really about getting a reusable hypersonic test drone and promoting private sector hypersonic technology development – not a hypersonic Air Force One.
Risk For A Speedy Reward
To meet the steep challenge the Air Force has set for it, Hermeus will have to design and build three prototypes by 2024 which can satisfy five USAF objectives from reusability to providing data for hypersonic wargaming fidelity and future payload integration.
Hermeus hopes to fly a vehicle in three short years by taking what might be called a poor man’s approach to hypersonic propulsion.
Rather than developing a highly complex, expensive air-breathing scramjet engine as used on NASA’s X-43 and the Air Force’s X-51 experimental hypersonic drones, Hermeus is using a simpler ramjet design based around the core of General Electric’s diminutive J85 turbojet which powers aircraft including the Air Force’s T-38 advanced trainer.
The engine will be what is called a turbine-based combined cycle (TBCC) design, mixing a conventional turbine (the J85) with a ramjet which, as the name implies, uses the engine’s forward motion to compress incoming air for subsequent combustion/thrust. The turbine accelerates the aircraft to a point where the ramjet can come online, adding additional thrust.
The fact that turbine and ramjet engines slow air to subsonic speeds for combustion, (unlike scramjets) makes them far easier to work with and scale. But while ramjet TBCCs work well at supersonic speeds around Mach 3, they struggle to reach hypersonic speed (Mach 5).
Experts like Luca Maddalena, a hypersonic flight researcher at the University of Texas, Arlington, say that may limit Quarterhorse’s ability to be a truly hypersonic research aircraft.
Hermeus’ CEO, AJ Piplica, acknowledges that whether Quarterhorse can reach hypersonic speed with its engine package is a question. He says his design team has “picked a technology set that allows us to develop vehicles in that Mach 3 to 5 range.”
“We wanted to stay as simple as possible, within the realm of technology that was relatively mature.”
It’s an approach that makes sense for a smaller private firm without unlimited capital. Prior to the Air Force investment, Hermeus obtained seed round funding from Khosla Ventures in 2019. Owned by Vinod Khosla, co-founder of Sun Microsystems, the Menlo Park-based venture capital firm was joined in 2020 by Silicon Valley neighbor, Canaan Partners, which led the 2020 series A investment in Hermeus.
Veterans of hypersonic R&D attest that nothing about it – from wind tunnel time to materials engineering to cope with intense heat – is cheap. Logically, the question arises whether $60 million is enough for Hermeus to bring Quarterhorse and follow-on vehicles to fruition?
Piplica replies that he’s “very comfortable with the company’s access to capital,” indicating it has more in the pipeline. That’s reassuring given his acknowledgement that Hermeus is pushing itself to develop a vehicle that could “touch Mach 5”.
The Quarterhorse prototypes and subsequent Hermeus-developed vehicles he says will determine operationally relevant speeds for reusable military and commercial aircraft whether hypersonic or near-hypersonic. That includes the passenger-hauler the company hopes to have flying by the end of the decade.
“By the time we get to flying passenger aircraft is it going to be Mach 5, Mach 4.5? We’ll see. Ask me again in five years.”
Upsized With A Space Launch Flavor
An important detail missing from the coverage of Quarterhorse thus far is its size. The X-43 and X-51 demonstrators were relatively small drones at 12 and 25 feet in length respectively. According to the Air Force, Quarterhorse will be 40 feet in length, about the size of a T-38. It will land and takeoff conventionally in about 7500 feet.
The jump in scale of its TBCC from the small, static test engine that Hermeus previously demonstrated for the Air Force is impressive. The flight engine will be approximately 10 times as large.
It’s not unreasonable to think of pushing the jet trainer-sized Quarterhorse (named for the American sprinter horse breed) to Mach 5 as a 10X challenge, the kind of quest the space launch industry has recently embraced with its privately developed, vertically-recovered, reusable orbital vehicles.
AJ Piplica and the three other principles with whom he founded Hermeus have space/space launch backgrounds with stints at Blue Origin, SpaceX and NASA among others. Much of the firm’s engineering talent comes from the same places. It’s partly a concession to practicality Piplica observes.
“The number of people who’ve built hypersonic systems is very small, even smaller than the number who’ve tested them.”
By bringing space launch talent into the fold Hermeus is organically satisfying one of the Air Force’s investment aims.
“Ensuring that we are developing the human capital, test infrastructure, and long term capabilities in hypersonics is a key priority,” Colonel Nathan Diller (USAF), director of AFWERX affirms.
In fact, the Air Force is so motivated to cultivate private sector hypersonic ventures that it may stand up a Quarterhorse program executive office early to help shepherd Hermeus and others across the so-called “valley of death” according to Col. Diller.
The USAF is not the only player that would look favorably on Hermeus’ success. The same researchers who question the company’s ability to go hypersonic with its design add that enlarging the pool of new, younger blood into hypersonic research is vital.
Luca Maddalena points out that any reusable addition to the small fleet of hypersonic research aircraft will be enthusiastically welcomed by the academic community who’ll get in the cue to gain access for flight testing and data review.
Whether the Air Force ultimately realizes a presidential transport from this exercise or not, a commercial hypersonic bizjet or airliner is a useful stalking horse in the bigger picture Piplica says.
“For developing the workforce in hypersonics, I think giving people an ideal or mission to work toward that isn’t just weapons or defense systems creates a whole new pipeline of talent.”
While the people-connecting mission that supersonic transport developers Boom, and formerly Aerion, espoused may attract idealistic university students to the field, Piplica reckons commercial applications also attract a bigger swath of private capital, further speeding development.
Greenfields & Bulk Value
A new 110,000 square-foot headquarters/factory where Quarterhorse airframes will be built and tightly integrated with their powerplants is being fitted out in northeast Atlanta. Hermeus’ static engine test facility is five miles away.
It’s a Lego-like structure of maritime shipping containers the company designed itself and built with a construction partner in Atlanta. It sits on a patch of green grass adjacent to to retired runway 27 at DeKalb-Peachtree Airport. The company calls it “Site 27” and they’ve already conducted over 50 engine runs there.
The pastoral, if occasionally loud, setting reminds one of aviation in general and the Biden administration’s push to decarbonize it completely by 2050, possibly looking to eliminate pure fossil fuel as jet fuel by 2025. To date, no alternative fuels have been investigated for hypersonic propulsion.
How does funding R&D from which a hypersonic transport might someday emerge square with the President’s objectives?
The Presidential and Executive Airlift Directorate’s Lt.Col. Burger responds, “When it is time for us to evaluate future presidential executive airlift requirements, having Hermeus as a competitor is valuable. Those goals set by the current administration will be taken into account as we evaluate an aircraft for recapitalization.”
Hermeus’ CEO says synthetic aviation fuels, carbon capture and other measures could square the circle on green hypersonics while acknowledging no practical solutions presently exist.
“To some extent we’ll lean on what the operators are going to do, the airlines and the DoD,” he explains.
Explaining what matters most to the Air Force can be divined by asking which of its five objectives for Quarterhorse rise to the top of the list. Lt.Col. Berger says developing a payload integration guide is at the forefront. The Air Force’s “appetite for subsystem risk reduction at hypersonic speeds is high,” he affirms, acknowledging that ISR, command-control and video are logical hypersonic vehicle payloads.
The service is also interested in examining communications systems – communications and data are difficult to transmit/receive at hypersonic speed – with Quarterhorse. But Piplica says the drone will have just 2 to 3 feet of volume and only 100 pounds capacity for a payload. As such, lessons-learned may be more limited than the Air Force would like.
Simply flying a reusable hypersonic research vehicle to gain real world data is also a prime objective. The fidelity such input can give to Air Force wargaming – operational/tactical concepts, acquisition roadmaps and more – is highly sought after.
“The bulk of the value that comes from this,” Burger stresses, “is the information we garner to inform future decisions, both budgetary programs of record and also for the impact of reusable hypersonic aircraft at various scales.”
“The vehicle’s purpose is really to flight test the engine,” Piplica allows.
The ancillary benefit for Hermeus is the potential to accelerate its own hypersonics roadmap, a course that includes a number of intermediate applications for hypersonic drones and the revenue they might generate before/if the company progresses to building a transport.
It’s a risky enterprise, one that Piplica calls “hardware rich” in the tradition of USAF fighter development of the 1950s-60s or of the SR-71, created with slide rules in two years’ time. “If we weren’t taking some pretty substantial technical risks in this program, then we wouldn’t be doing our jobs,” he says.
The Air Force is “partnering boldly” on Quarterhorse Lt.Col. Burger opines. “The byproduct will be learning, whether fully or partially successful.”
The byproduct won’t be a hypersonic presidential transport anytime remotely soon. Perhaps a future president can dream of that. In the meantime, the would-be commander-in-chief can buy Hermeus merch.