Quarterhorse: The Future of Hypersonic Flight

It has been six decades since the SR-71 Blackbird first took to the skies, and yet it remains, even today, at its place atop the mountain of global aviation. No manned, air-breathing aircraft has ever flown faster or higher, nor dared to brush so close to the edge of space itself. Since it was retired, rumors have abounded of successor craft that could do more, fly even better, than the Blackbird ever could, but they have remained just that: rumors, banished to aviation legend with no promise that the truth will ever be revealed.

But roaring to life out of Atlanta, Georgia, is a fast-growing organization that intends to blow the SR-71 clean out of the record books. Its name is Hermeus, and already, it has drawn comparisons to Lockheed Martin’s Skunk Works both for its ambition, and its immense technical potential. Yet even more captivating than the Hermeus company itself, is its flagship project, a series of aircraft known as the Quarterhorse line, with the ultimate objective of shattering the SR-71’s airspeed record once and for all.

In this examination of the Quarterhorse aircraft, we will be taking a closer look at how they are made, what they will be able to do, and why, after a long line of aircraft proposals from companies far bigger and more famous than this one, Quarterhorse might just be the one to make its vision into reality.

Meet Hermeus

In order to understand the Quarterhorse aircraft, we have first got to understand the company behind it. A recent start-up founded in 2018, and led by CEO and aerospace engineer AJ Piplica, Hermeus has very quickly become a darling of the venture-capital world. Big names like OpenAI’s Sam Altman and tech entrepreneur Peter Thiel have poured cash into the project, encouraged, in part, by the expertise of the organization’s leaders.

Prior to founding Hermeus, Piplica and his top executives led Generation Orbit Launch Services, a group that was instrumental in developing a hypersonic testbed aircraft for the US Air Force that was eventually designated the X-60A. In an industry known for its flights of fancy around bold, high-supersonic aircraft designs that never manage to get built, Hermeus has already developed a strong reputation, not just for its technical vision, but for its apparent potential to actually make good on what it has promised.

Uniquely for a relatively small, relatively young company, Hermeus has already proven itself able to produce new technology demonstrators at high rates. Rather than waffle on about funding constraints or stay vague about what it hopes to achieve, Hermeus has made a reputation for itself with a timeline to crank out its flashy new toys quicker, and with greater operating efficiency, than any other private company in recent memory. In fact, they have drawn comparisons to the early years of Lockheed Martin’s Skunk Works, responsible for generation after generation of groundbreaking aerospace innovation, not just for the scope of Hermeus’ ambition, but also for its ability to actually produce tangible products along each step of the way. As journalist and defense expert Alex Hollings described the company in a recent YouTube episode for Sandboxx: “This Hermeus team has the technical prowess, they have the pragmatic optimism, and they have the audacity to change the world all over again.”

Those sorts of distinctions are very important for a company like Hermeus, at a moment in time when the American military is increasingly open to relying on newer, smaller companies to produce new ideas and technology demonstrator craft. With well-established aerospace companies like Lockheed Martin, Northrop Grumman, and Boeing, already hard at work developing incredibly sophisticated future aircraft, both the US Department of Defense, and the private world of venture capitalists, have started to branch out toward other organizations that have the requisite knowledge to take the United States even further. But when it comes to actually putting money down in support of new startups, the Pentagon has been far more skeptical; after all, it is all too common to see even the best-intentioned organizations fail to deliver even after they receive the massive checks they ask for.

But when it comes to the current field of startups, especially those brave or foolish enough to believe that they can take on the prospect of hypersonic flight, Hermeus is head-and-shoulders above the rest. And just as important for a company hoping to make a major impact, they appear to be at the right place at the right time.

The Hypersonic Challenge

Before we actually get into specifics on the Quarterhorse line, we have got to be specific about what kind of problem Quarterhorse is supposed to solve. There are many, many barriers that make hypersonic flight difficult to achieve, but “hypersonic flight” itself is not a monolith. By example, ballistic missiles have been more than able to travel at hypersonic speeds for decades—and, by the way, hypersonic speeds are anything at or above five times the speed of sound. But ballistic missiles, rockets, and other vehicles that can consistently achieve hypersonic flight, do it in parabolic arcs where they fly very high up into the sky, level off, and, if they are going to return to Earth, fly basically straight down toward the ground. They have got only minimal ability to maneuver, and they cannot really evade air defenses, so while their hypersonic speeds certainly confer a lot of benefits, they are not nearly as good as they could be.

What Quarterhorse, the US government, the governments of Russia and China, and anybody else on the cutting edge of aerospace design really wants to achieve, is the capacity to achieve hypersonic flight without leaving Earth’s atmosphere, during sustained level flight. Imagine something that can fly like an airplane, but do it while going bloody fast. When it comes to that sort of mission role, the SR-71 is still the best operational aircraft in history, although it still fell far short of the Mach-5 criterion to go hypersonic. The US and other nations have what is called boost-glide vehicles, ones that use rocket boosters to achieve hypersonic speeds, but those are very difficult to design in a way that would get them to a target and enable them to come back, without dropping below hypersonic speeds. So, these are more likely to be one-way systems like missiles, or drones that are not likely to slow down enough that they would be recoverable after, let us say, smashing into the sea after they have flown over a target. There is also experimental technology like scramjets, specialized engines that allow fuel combustion to take place while the air present in the engine is moving faster than the speed of sound, which should enable high-performance, high-efficiency flight at extremely high speeds. Unfortunately, though, these are still very much in the experimental phase, and because scramjets do not work at subsonic or low-supersonic speeds, any aircraft that uses them also has to have a second propulsion system onboard in order to get to their required speed to function.

Most challenging of all, is the prospect of designing an aircraft that can take off from a runway, get up to supersonic speeds, then go hypersonic, before slowing down again to speeds that would allow it to land intact and perform more missions in the future. With current technologies, that is a really hard ask for even entire governments to achieve. As recently as 2023, the US Pentagon estimated that even one single-use hypersonic missile could cost more than a brand-new F-35A, meaning that a reusable, recoverable hypersonic aircraft should, in theory, be much more expensive…except Hermeus begs to differ. According to the startup, it should be possible to field a reusable hypersonic aircraft not for an order of magnitude more than the price point of a hypersonic missile, or for two or three times the price, but for roughly the same—meaning that if Hermeus’ calculations are right, then the company has the potential to completely upset the conversation on hypersonic aircraft. And the path to getting there, runs directly—and exclusively—through the Quarterhorse.

The Quarterhorse Line

When we consider the nature of the Quarterhorse aircraft, it is important to preface what we are about to see with the fact that these are technology demonstrators. None of the designs we will explore from Quarterhorse, not even the finished product, are ever expected to be able to fulfill a role with the US military or any other. Instead, they are meant exclusively to prove that Hermeus’ proposed technology solutions, have the potential to work as well as the company says. Prove that, and that is when the real party starts, as Hermeus’ technology gets snapped up by the Department of Defense, and the design once known as Quarterhorse begins to evolve into a weapon.

The Chimera Engine

The program starts with the element at the core of any hypersonic aircraft: the engine. In Hermeus’ case, they use a homegrown, first-of-its-kind engine called the Chimera, which holds the distinction of being the world’s first commercially developed turbine-based, combined-cycle engine. This, alone, is a very impressive piece of engineering, a unique engine design that marries a turbojet—the powerful, but low-supersonic engines that can be found on today’s fighter aircraft—with a ramjet, a hypersonic-capable engine that includes a mechanism to compress incoming air to subsonic speeds, fire it through an engine, and produce speeds well above Mach 5 for the aircraft that carries it.

Already, Chimera has proven itself to work, pushing first into turbojet mode before cycling up to its ramjet function, and then cycling back down to turbojet, all in one engine. When in flight, the turbojet component will be capable of bringing an aircraft up to around Mach 2 all by itself, before the ramjet kicks in and works together with the turbojet, to bring the aircraft up to about Mach 3. Then, the turbojet switches off and the ramjet takes over, in a process that goes in reverse when it is time to slow down to subsonic speeds.

Even more important, Hermeus was able to go from zero to a fully functional Chimera in just the span of twenty-one months, and for the shockingly low cost of 18 million dollars US. Hermeus was able to 3D-print a full fifteen percent of the Chimera’s components, and build it in-house using an older-model General Electric J85 turbine that is, as Hermeus describes, “readily available, off-the-shelf”. In fact, it is the same engine used in the F-5 fighter aircraft and the T-38 trainer aircraft, of which nearly 4,000 have been constructed worldwide.

A hypersonic aircraft that can carry Chimera onboard will have no need for a rocket, no need to find extra space within the airframe for a separate hypersonic-capable engine, and the capacity to be easily maintained and turned around for subsequent flights.

Quarterhorse Mk 0

Then, there are the Quarterhorse technology demonstrators themselves, starting with the Mk 0 craft. Fitting with its designation of zero, this particular demonstrator is capable of exactly zero flight, but it is not intended to be a flyable aircraft at all. Instead, Mk 0 is an ode to the idea of walking before you can run, something that Hermeus achieved in 2023, when the Mk 0 began taxi tests on the ground.

Remote-operated, stripped down to the bare bones, and less than forty feet long, the Mk 0 is not much to look at. But nonetheless, it was a critical piece of Hermeus’ approach to building a craft—what it refers to as “rapid prototyping”. As Hermeus itself explained in a press release, “Rather than consolidating all uncertainties and variables into a single Mach 4 aircraft, we are spreading the risks across multiple vehicles, which will enable us to learn more quickly.

This iterative, hardware-intensive method is our key to speeding up aircraft development.” By all accounts, Mk 0 was a success, clearing the electrical, hydraulic, pneumatic, steering, ground propulsion, and command-and-control systems Hermeus intends to use, so that now, as they progress to bigger and badder prototypes, no more time will have to be wasted validating those systems.

Quarterhorse Mk 1

And by all outward indicators, Hermeus wasted no time at all in getting to the Mk 1. Built and ground-tested while the Mk 0 was still completing its own tests, the Mk 1 is the first real-life aircraft that Hermeus will send up into the sky. Powered by the same GE J85 engine that has since been adapted into the Chimera, Mk 1, like the rest of the Quarterhorse line, will be uncrewed.

It incorporates software and hardware changes based on lessons learned from the Mk 0, and its primary purpose is to demonstrate that it can take off and land at high speed. The “high speed” portion is particularly important, since it is that critical element that would make a hypersonic aircraft of this type practically feasible. The same narrow-body, narrow-delta-wing design that allows hypersonic aircraft to slice through the air at speed, makes it impossible to slow down to normal-plane speeds to land.

Instead, the Quarterhorse, with its sleek design, will need long runways to do its work, something that the Mk 1 will get squared away rather quickly. But even before it flies, the Mk 1 has scored a major success; wrote Hermeus CEO AJ Piplica on X: “We designed and built this airplane—from scratch, like literally napkin to airplane—in 204 days. Let that sink in. 204 days.

The standard here is about 1,400 days – 3.5 years. We missed the P80 record by 61 days. This is the way.”

Quarterhorse Mk 2

And if the Mk 1 is about getting into the sky, then the Mk 2 is about showing exactly what this Quarterhorse platform is really capable of. About the size of an F-16, hauling a Pratt & Whitney F100 engine that will be modified into a more advanced Chimera successor, the Chimera II, the Mk 2 is not about beating the Blackbird—at least not yet—but it is about trouncing the competition of the 21st century. Capable of hitting high-supersonic speeds just south of Mach 3, the Mk 2 will aim to go faster than nearly every manned fighter aircraft and unmanned UAV on the planet, at least the ones that are publicly disclosed. With that, the Mk 2 will become the fastest re-usable jet in history, as well as the first high-Mach autonomous aircraft in the world. As of now, Hermeus is believed to be well on the way to having a working Mk 2 in its hands, equipped with parts manufactured rapidly via titanium 3D printing, and designed using iterative improvements on the Mk 0 and Mk 1 in real-time as those prior platforms were tested. The company’s profile on X promises a big reveal in the summer of 2025, keeping pace with the delivery schedule they have promised: one aircraft per year.

Quarterhorse Mk 3

Finally, there is the Mk 3, the end-stage of the Quarterhorse line. It is the Mk 3 that will beat the Blackbird’s airspeed record, flying at expected speeds past Mach 4, bringing it just to the edge of true hypersonic flight. To do that, the Mk 3 will be the first Quarterhorse model to use the Chimera II engine to its fullest potential, and carry out the complete cycle from turbojet, to combined propulsion, to pure ramjet, and back down.

It is not yet clear whether Hermeus will push the Mk 3 past the threshold to hypersonic flight, or whether they will settle for claiming the all-time airspeed record for the world’s fastest aircraft, but in theory, the Mk 3 will have the capacity to break that final boundary as well. Its anticipated top speed is said to be somewhere around Mach 5.5, or just over 4,200 miles per hour—fast enough to cross the continental United States in some forty-five minutes. As for when the Mk 3 will emerge, Hermeus’ own promises would suggest that it will be out in the world, in some form, by the end of 2026, and judging by the company’s ambitious testing schedule, it will likely take to the skies soon after.

Progress and Potential

As of now, Hermeus is charging through its estimated progression of technology demonstrators, with no end in sight. At the end of March 2024, the Mk 1 was unveiled to the media, revealing a stripped down, but very impressive-looking aircraft sporting a cylindrical fuselage, a delta wing set far back across its length, and a long, pointed nose with an engine air intake just below. It is expected to take its first flight in the summer of this year.

In other news for the Quarterhorse series, Hermeus recently signed a multi-year contract to partner with the US Department of Defense’s Defense Innovation Unit, in order to use Quarterhorse as a testbed prototype for other advanced technology relating to hypersonic flight. While the DoD has at least seventy programs across the military focused toward developing the requisite tech to make hypersonic flight happen, it lacks airframes in order to actually see whether that technology works. Hermeus has the Quarterhorse, available in up to four distinct editions, each of which can be reproduced and used for testing depending on what the Pentagon needs.

Military Applications

And what the Pentagon needs, might turn into a much more expansive slate of next steps for Quarterhorse. Although the Mk 1 prototype is not likely to be a ton of use, on account of how the US military already knows how to take off and land aircraft at high speeds, the Mk 2—with its UAV design and capacity to fly just as fast as any manned aircraft in America’s current arsenal—is a candidate to be modified into several mission roles. If even the Mk 2 were to enter service with the US, capable of flight up to around Mach 3, it would immediately become the fastest known UAV in the American arsenal. Strap a camera to it, and it offers unparalleled reconnaissance capabilities, filling a role that, at least officially, has not been accounted for since the Blackbird left service. In its hypothetical ISR role, the Quarterhorse might become a priority for the US military on its own, or be wrapped up into a larger program called Replicator, which the Pentagon intends to use to field a massive fleet of drone aircraft in the coming decade or so.

Beyond just its potential to fill a high-speed, unmanned ISR role for the US military—that is intelligence, surveillance, and reconnaissance—the Mk 2 also has considerable potential to serve as part of America’s so-called “Loyal Wingman” program. This is an ongoing effort that runs alongside the United States’ attempt to field a sixth-generation fighter aircraft, the Next-Generation Air Dominance program, although since its conception, aerospace and defense experts have speculated that the Loyal Wingman could go well beyond just the NGAD. The basic idea here is that the planes of the future, as well as the advanced models of the F-35 in service today, will be able to operate at the heart of small formations mostly comprising unmanned drones.

Those drones might be able to do anything from carrying extra weapons or electronic warfare equipment, to distracting an enemy air force, to even, one day, dogfighting and actively engaging in aerial combat operations. At present, it appears that the US is looking to field not just one line of Loyal Wingman drones, but a whole collection, adding and integrating new capabilities as they become feasible. If Hermeus’ Mk 2 drone continues to develop at its current pace, it should be able to physically keep pace with the F-35, the Next-Generation Air Dominance aircraft, and the other fighter, bomber, tanker, and early-warning-and-command planes that are likely to leverage Loyal Wingmen in the future.

The only question, then becomes whether the Mk 2—or even the faster Mk 3 successor craft—can be fitted with the requisite technology and equipment to be useful in that role.

Darkhorse: The Military Endgame

And for Hermeus, the Quarterhorse Mk 2 and 3 are still just the beginning. Next up, after the Mk 3, is the Darkhorse, the military uncrewed aircraft that Hermeus really wants to build. Powered by two side-by-side Chimera II engines, the Darkhorse is intended to be a fully hypersonic aircraft, designed specifically for use by military clients—meaning, in the case of Hermeus, the United States. It will measure a length of about 45 feet, and at a minimum, its Mach 5 speeds will put it at a top speed of 3,850 miles per hour—with an actual top speed well above 4,000 miles per hour, being somewhat more realistic. As of now, details on the Darkhorse’s ultimate purpose—other than its incredible speed—are as-yet unknown. But a platform with those capabilities would almost certainly be effective in fulfilling ISR duties, and if Hermeus or someone else can develop relatively affordable weapons that can either launch from a hypersonic platform and attain hypersonic speeds themselves, or decelerate in a way that both scores a hit on a target and avoids disintegration, then the Darkhorse has the potential to become a new worst nightmare for America’s adversary nations around the world.

No matter what else, the Darkhorse is very clearly meant to be a reusable platform, potentially costing as little for the US government as 100 million US dollars per plane. If that is a mind-boggling amount on paper, worry not; in reality, it is just a bit under the per-plane cost of the F-35, at least using current cost and production estimates on the F-35 program, less than a third of what the F-22 program cost per-plane several decades ago, and well under a tenth of the cost of a B-2 Spirit bomber. Those numbers, by the way, are not the sticker price advertised for each of those planes, but instead the program’s actual cost, divided by the number of aircraft that were ultimately produced.

Per Alex Hollings, who we referenced previously, the Pentagon’s current price estimates to procure just one single-use hypersonic missile run as high as 106 million US dollars—and that is for a piece of technology that will either detonate on impact with a target, disintegrate when it hits land or sea, or be, in some other way, completely unrecoverable. For Hermeus to produce a multi-use aircraft that can hit the same speeds, at a lower cost, would be game-changing for America and its allies, as well as anybody else who can get their hands on a Darkhorse aircraft.

Halcyon: The Civilian Vision

And Hermeus’ ultimate ambitions extend even beyond the Darkhorse line. The final grand project on the company’s slate—or, at least, the longest-term goal they have publicly announced so far—is not a military project at all. Known as Halcyon, the aircraft Hermeus ultimately hopes to produce would be a passenger aircraft, capable of hitting hypersonic speeds and performing trans-oceanic routes across the globe.

According to Hermeus’ website, the Halcyon would be capable of running a route from New York to London in 90 minutes—including not just hypersonic flight, but the acceleration and deceleration processes involved to go from airport to airport. That is so fast that it would save a full six hours of one-way flight on every journey. Marketed toward business-class customers, the 20-seat Halcyon will tap into a market that currently sees half a million business customers fly from New York to London annually, and potentially grow that market, as well as other international-route air markets, exponentially as a result of the new aircraft’s capabilities.

Per Hermeus, hypersonic travel along these routes has “the potential to add more than $4 trillion of global GDP growth per year by radically accelerating the speed of commerce and cultural exchange”. According to a feature done by CNN back in 2021, Halcyon will feature a range of some four thousand miles—not enough to cross the Pacific, but enough to enable trips from Boston to Mexico City, Singapore to Tokyo, Beijing to New Delhi, London to Lagos, Paris to Dubai, and many more intercontinental pathways that are relatively under-utilized today, but could become immediately feasible if Halcyon can take to the skies.

Limitations and the Road Ahead

Unfortunately, the entire Hermeus line of planned aircraft do have a key drawback; specifically, they have all got a speed limit. Granted, it is a very, very high speed limit, but nonetheless, it is unlikely that a ramjet-powered aircraft like the Quarterhorse line would be able to push past roughly Mach 6. Make no mistake, that is still very, very good, but so-called scramjets, which do not require air to slow down to subsonic speeds, can theoretically boost an aircraft to Mach 10 or even further. Where this becomes an issue, is if Hermeus wants to stay competitive—not with the industry that exists today, but with the one that might exist twenty to thirty years from now, when the Darkhorse and the Halcyon are just two among a wide variety of aircraft capable of extraordinary things. For now, Hermeus will be just fine; according to public knowledge, no nation, and no private company, has ever been able to make a scramjet work in anything more developed than a technology demonstrator. But in order to keep its edge for the future, Hermeus will need to address that scramjet issue. Perhaps, they will do it by designing an even more revolutionary turbo-to-ram-to-scram Chimera III engine, perhaps by building aircraft that integrate Chimera-style engines with additional scramjets, or perhaps by working to shift the way the market will work. Prove that an aircraft that operates at, or just past, the doorstep to Mach 6 is capable of doing anything you could ever want, without the costly addition of a scramjet at all, and the incentive to grow into a new niche is replaced by incentives to excel at a niche where Hermeus is already building a considerable edge on the competition.

Conclusion

But whether Hermeus ultimately becomes an enduring symbol of flight innovation, trekking across the same hallowed ground as Skunk Works and a tiny handful of other peers, or whether its contributions are tied only to this moment in time, one thing appears relatively clear—or, that is, as clear as predictions around highly ambitious engineering can ever be. We will not go so far as to claim that Hermeus is guaranteed to be the future…but there are a fair number of companies out there insisting that they will be the one to unlock the secrets of hypersonic flight, and quite frankly, there is a reason they are not the subject of this examination. Alongside its ambition, Hermeus has shown a rare degree of efficacy among its peers, not just dreaming big, but proving, year after year, that it can bring those dreams to life.

In twenty years’ time, we could be living in a world where hypersonic flight is practically normal, a new, but safe, trustworthy, and ubiquitous technology across the globe. Go back in time twenty years before this was written, and even just describing a first-generation iPhone would have generated more skepticism than optimism; time moves very fast, where truly valuable technological innovations are concerned, and hypersonic flight could work the same way. Or, in twenty years, we could be no closer to hypersonic aircraft than we are today, running up against a barrier that humanity just cannot seem to pass. What we will say, with a great degree of confidence, is that if we humans really can cross that barrier, then the Quarterhorse will be remembered as one of the aircraft most critical in getting there.

Key Takeaways

Hermeus aims to surpass the SR-71 Blackbird’s speed record with its Quarterhorse aircraft series.
The Quarterhorse line includes technology demonstrators like the Mk 0, Mk 1, Mk 2, and Mk 3, each progressively faster.
Hermeus’ Chimera engine combines turbojet and ramjet technologies to achieve high supersonic speeds.
The company has rapidly developed prototypes, with the Mk 1 built in just 204 days.
Hermeus’ ultimate goal is to create a reusable hypersonic aircraft for both military and civilian use.

Frequently Asked Questions

What is the Quarterhorse project?

The Quarterhorse project is a series of aircraft developed by Hermeus with the ultimate objective of shattering the SR-71’s airspeed record and achieving hypersonic flight.

Who is behind the Quarterhorse project?

The Quarterhorse project is led by Hermeus, a fast-growing organization based in Atlanta, Georgia, founded in 2018 by CEO and aerospace engineer AJ Piplica.

What is the Chimera engine?

The Chimera is a first-of-its-kind turbine-based, combined-cycle engine developed by Hermeus. It combines a turbojet and a ramjet to achieve hypersonic speeds.

What are the different models in the Quarterhorse line?

The Quarterhorse line includes the Mk 0 (ground-testing prototype), Mk 1 (first flyable aircraft), Mk 2 (high-supersonic speeds), and Mk 3 (aims to beat the SR-71’s airspeed record).

What is the Darkhorse project?

The Darkhorse is a fully hypersonic, military uncrewed aircraft intended to be a reusable platform capable of hitting Mach 5 speeds, designed for use by military clients.

What is the Halcyon project?

The Halcyon is a planned passenger aircraft by Hermeus that aims to achieve hypersonic speeds, capable of running routes like New York to London in 90 minutes.

What are the potential military applications of the Quarterhorse?

The Quarterhorse, particularly the Mk 2 and Mk 3 models, has potential applications in high-speed unmanned ISR (intelligence, surveillance, and reconnaissance) roles and as part of the Loyal Wingman program.

What is the significance of the Chimera engine’s development time and cost?

The Chimera engine was developed in just 21 months at a cost of $18 million, showcasing Hermeus’ ability to rapidly prototype and build advanced technology.

What is the current status of the Quarterhorse Mk 1?

As of March 2024, the Quarterhorse Mk 1 has been unveiled to the media and is expected to take its first flight in the summer of 2024.

How does Hermeus plan to address the speed limit of the Quarterhorse line?

Hermeus may need to develop a more advanced engine like the Chimera III or integrate additional scramjets to stay competitive with future hypersonic technologies.

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The Hypersonic Challenge