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The Science of Speed: Understanding Hypersonic Flight

Nancy Atkinson
Matt Morgantini
June 27, 202310:00 AM UTC (UTC +0)

A scene in last year’s Top Gun: Maverick depicts Tom Cruise piloting a hypersonic aircraft called the Darkstar.

In the blockbuster film, the fictional aircraft successfully reached speeds of over Mach 10 — or ten times the speed of sound — before it disintegrated in mid-air. Back in the real world, however, the fastest a piloted airplane — one capable of takeoff and landing — has flown is Mach 3.3, or 2,193 mph (3,530 km/h).

This record was set by the Lockheed SR-71 Blackbird, way back in 1976. 

But now a startup called Hermeus is looking to make hypersonic flight a reality for the rest of us, with the ultimate goal of a commercial passenger aircraft called Halcyon, and with a first flight perhaps as early as 2030. The company hopes to soon roll out a remotely-piloted prototype aircraft called Quarterhorse for testing, with ambitions for Mach 4 flight by 2024. For a company that was only founded in 2018, that’s a fast turnaround.

“We focus on using existing technology and materials rather than finding or founding new ones,” said Glenn Case, one of the company’s founders, and the Chief Technologist. “That means we are on the precipice of rolling out one of our first vehicles by the end of the year, heading towards our goal of radically accelerating air travel. Quarterhorse will enable us to de-risk the technology needed to build Halycon at a lower cost and without risking pilots onboard.”  

Hermeus has another hypersonic aircraft in the works called Darkhorse, a hypersonic uncrewed aerial system (UAS) with multi-mission flexibility designed for defense and intelligence clients. The company brands Darkhorse as representing a major technological leap, providing a capability matched by no other country in the world.

And the timing is important. The development of these hypersonic vehicles has recently become a top priority for the US Air Force, for deterring the hypersonic weapons currently being developed by China and Russia. 

Hypersonic So Far

Sustained hypersonic flight — or traveling faster than five times the speed of sound — has been a goal in aviation and for the military for decades. While rocket-powered missiles and space vehicles routinely achieve hypersonic speeds, hypersonic flight within the atmosphere in a crewed, winged aircraft has been problematic, despite years of research and test flights. The field of hypersonics has also faced decades of boom-and-bust cycles, with ups and downs in governmental interest and funding, ever since the U.S. started developing hypersonic aircraft in the 1950s. 

The technical challenges of sustained hypersonic flight are vast.

Reaching those speeds — past Mach 5 (3,806 mph or 6,126 km/h) — means having air-breathing engines capable and versatile enough to power the aircraft from takeoff and acceleration through Mach 1 all the way to Mach 5 and beyond. During flight, those speeds produce metal-melting heat and turbulence capable of ripping an aircraft to pieces. But the rewards of hypersonic flight would be revolutionary: passengers could fly from New York to London in 90 minutes — twice as fast as the supersonic Concorde.

Hypersonic flight is not totally unprecedented. In 2004, NASA flew the X-43A hypersonic test aircraft up to Mach 9.6. This unpiloted test aircraft was initially boosted by a rocket before switching to a "scramjet,” a high-performance air-breathing engine, which takes in air from the atmosphere to help burn its fuel. But the hypersonic portion of the X-43A flights lasted only 11 seconds. It was a glaring demonstration that keeping an engine running at those speeds is incredibly challenging.

Hermeus And Beyond 

One of Hermeus’ taglines is to “Bring Newspace to Aviation.” The four founders all have backgrounds working with Newspace companies. Case worked at Blue Origin, and later worked at Generation Orbit along with a trio of others who led the development of the Air Force’s X-60A hypersonic rocket plane. The foursome left to found Hermeus: CEO AJ Piplica, chief product officer Mike Smayda and chief operating officer Skyler Shuford. Smayda and Shuford also had stints at SpaceX.

“While everyone in the industry seemed to be focused on small launch, we knew there was a real keen need in the military for high-speed systems and in particular air-breathing engines,” Case told Supercluster. “So we decided to kind of jump off a cliff in 2018. And try to build an airplane on the way down.” 

The sleek, rendered designs for the three planned Hermeus vehicles show smooth, blade-like surfaces with wings blended into the body, much like the SR-71. The design is all in the name of thermal management, and to reduce drag, said Joe Schoneman, a Loads & Dynamics Analyst at Hermeus. Schoneman said that while Quarterhorse is about the size of the Air Force’s T-38 jet (about 50 feet, with a 15 ft wingspan), upcoming flight tests will help improve the future designs of Darkhorse and Halcyon. 

“Once we have flight experience with Quarterhorse, how our models and designs line up with reality is going to inform [the design],” Schoneman told Supercluster. “This is inherently a very iterative process.”


But it is the Hermeus engine design that sets them apart.

Instead of developing a highly complex and expensive air-breathing scramjet engine like ones on NASA’s X-43 and the Air Force’s X-51 experimental hypersonic drones, Hermeus is using a simpler ramjet design based around General Electric’s smaller J85 turbojet, which powers other aircraft today, including the T-38.

Called Chimera, their engine is a turbine-based combined cycle, or (TBCC), which is a hybrid between a turbine engine and a ramjet, allowing for both low-speed (takeoff, cruise, and landing) and high-speed operation during flight. This is unique in the field of hypersonics. Hermeus says that by making a full-range air-breathing hypersonic engine that does not require a rocket to accelerate, they will have an aircraft that can be rapidly re-used. And a Chimera-powered aircraft would be able to take off from any major runway and return to land at the same airport. This is far less complicated and requires less infrastructure than an aircraft dropped from a larger carrier, or propelled from a rocket. 

One of the most complex parts of the engine’s operation is the transition from turbojet to ramjet.   

“Several things have to go right in a very short period of time,” Case explained, “because you have to effectively turn off the turbojet and turn on the ramjet while maintaining stable flight.” 

The Hermeus team conducted a successful test of Chimera at the Notre Dame Turbomachinery Lab last year, where high-speed Mach 4 flight could be simulated. The test campaign lasted five months, and engineers ran the jet in bursts, repeatedly demonstrating a stable transition from turbojet to ramjet.

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“We are the first privately funded commercial company to have ever done this, and we did it for an order of magnitude less time and money than any governmental program,” said Case. “So, we demonstrated the capital efficiency that a Newspace-type company can bring to the game. But more importantly, the test gave us a lot of great data to help us with some component redesigns to make the engine more efficient.”

That puts Hermeus on target for its lofty goal of reaching Mach 4 speeds by next year. 

And it would break the sustained airspeed record set by the SR-71.

Why Hypersonic, Why Now?

Over the past few years, several other private companies have begun to develop new hypersonic aircraft, with similar goals to significantly advance the United States’ ability to design and operate hypersonic vehicles.

In 2020, high-altitude launch company Stratolaunch revealed designs for two hypersonic aircraft, plus a reusable space plane that will be launched from its giant Roc Carrier Aircraft launch plane, similar to Virgin Galactic’s White Knight Two. Stratolaunch’s hypersonic planes are called Talon-A and Talon-Z, while the space plane is dubbed Black Ice.

The Talon-A is planned to be a fully reusable, autonomous, liquid rocket-powered Mach 6-class hypersonic vehicle with a length of 28 feet (8.5 m) and a wingspan of 11.3 feet (3.4 m). The first tests, perhaps by next year, will last for “over 1-minute of hypersonic flight testing, and glide back for an autonomous, horizontal landing on a conventional runway,” according to Stratolaunch. 

And earlier this year, Rocket Lab announced a hypersonic program called HASTE (Hypersonic Accelerator Suborbital Test Electron), a suborbital testbed launch vehicle derived from Rocket Lab’s heritage Electron rocket. On June 17, the company successfully conducted its first launch for “a confidential customer” (likely the US military), from Virginia’s Mid-Atlantic Regional Spaceport within NASA’s Wallops Flight Facility. Rocketlab says their hypersonic program was created to serve the unique needs of the U.S. defense and intelligence community and its allies.

And of course, long-time companies like Lockheed Martin, Northrop Grumman, and Raytheon are part of a revitalized interest in hypersonic vehicles and missile defense following recent intelligence that China fielded a test in 2021 of a hypersonic, nuclear-capable weapon, and Russia’s recent use of hypersonic weapons in its invasion of Ukraine. Australia, Iran, both North and South Korea, Brazil, Germany, Israel, India, and Japan are also said to be developing hypersonic programs. 

There’s been relatively little US investment in these systems in recent decades, but that has changed.  According to a January 2023 report from the Congressional Budget Office, the Department of Defense’s proposed budget for Army and Air Force hypersonics development for 2023-2027 now sits at $15 billion, along with the Navy’s hypersonic development program, which recently announced a $1.1 billion contract with Lockheed Martin.  

There’s a sense that the US is now playing “catch up.”

“I think it's one of the biggest travesties of American technology development, how we’ve fallen behind when we were so far ahead in terms of hypersonic research,” Case told Supercluster. “What we had was built on the shoulders of giants, with the X-15 flying virtually every week in the 1950s and 1960s, but then the focus shifted to space. Then in the late 1990s and early 2000s, we had the X-43 and X51 testing in scramjet development, but it stopped because the adversarial threat wasn’t there at the time. To be honest, the U.S. sat by the sidelines. Now we're playing catch-up.” 

Case and Shoneman both mentioned that much of the hypersonic research developed during these boom periods was published and became public, so those now considered “adversaries” of the United States were able to stand on the shoulders of giants, too. 

In this new boom period, Hermeus hopes to ride the current wave of hypersonic interest.

“I think developing reusable hypersonic systems is one of the most important things that aerospace engineers could be doing right now,” Case said. “Hypersonic passenger flight would be game-changing for everyone. And without being able to go into too much detail of what Darkhorse will be capable of, the one thing that really sticks with me is that it’s a platform with the capability to keep the U.S. ahead of others. And keep us out of war.” 

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This story is sponsored by Hermeus. Hermeus is on a mission is to radically accelerate air travel with Mach 5 aircraft to bring much needed innovation to commercial flight.
Nancy Atkinson
Matt Morgantini
June 27, 202310:00 AM UTC (UTC +0)