An aircraft running on hydrogen that races through the upper atmosphere at speeds exceeding twelve times the speed of sound might seem like a fantasy reserved exclusively for science fiction. That, however, is the promise behind the Australian Hypersonix Launch Systems’ DART AE demonstrator, a small and uncrewed vehicle that is built around the SPARTAN scramjet, a completely new kind of engine. The immediate objective of this development program is not to make this aircraft a vehicle for passenger travel but rather a recorder for flight data. Hypersonic speeds are difficult to validate unless an actual prototype takes to the skies, as ground facilities are incapable of reproducing the shock heating, turbulent flow, engine ignition, and precise speed control at Mach 5.

This is an engineering spring that will ultimately mix propulsion, materials, autonomy, and carefully coordinated testing logistics, all scenarios where small slips will snowball quickly. At the same time, the world’s first claim needs additional framing here. NASA built an X-42A hydrogen-powered scramjet to reach speeds of Mach 9.6 for a brief moment in 2004. Therefore, this new unmanned aircraft would be more of an optimization and refitting of an existing technology. The pitch that Hypersonix has given is that this new aircraft will offer faster build cycles, more launches, and longer powered runs. Those who back the program also emphasize the use of green hydrogen, ultimately positioning this program as both a defense-relevant aircraft capability and a cleaner overall propulsion experiment. We analyze this ambitious development program and what it could bring to the table in detail.

What Exactly Is A Scramjet?

For starters, we need to begin by adequately defining what exactly a scramjet is. The word « scramjet » is a syncopation of supersonic combustion ramjet, which is a kind of engine that has no fan or compressor. Instead, this kind of engine relies exclusively on a vehicle’s forward speed in order to squeeze incoming air. At speeds of around Mach 5 and above, the inlet itself shocks, and the duct geometry helps compress the airflow to high pressure and temperature.

Then fuel is injected and burned while an aircraft is in the air and while it remains moving supersonically through a combustor. That is both the magic and the headache. As the residence time for this kind of engine is minuscule, fuel is forced to mix and ignite extremely fast. The flame itself must stay anchored without choking off overall airflow. At the same time, the airframe and the engine become the same object, with the body helping form the engine’s inlet while the nozzle contributes to overall lift and generates thrust.

This is why scramjet engines are traditionally paired with rockets or other boosters, as they do not allow for a vehicle to taxi and then slowly start up like a turbine engine. Even small changes in angle of attack or heating can seriously upset a scramjet’s combustion stability, highlighting the volatility of these kinds of engines. When a program promises high Mach numbers, the question is not only peak speed but also how the engine itself will keep the aircraft at this speed, and if pilots will be able to steer with any actual form of accuracy.

Why Does Hydrogen Help Generate Higher-Speed Performance?

Hydrogen is incredibly attractive for scramjet engines, partially because the element is chemically eager to combust. Hydrogen atoms diffuse quickly, mix quickly with fuel, and can ignite over a wide range of conditions. This offers exactly what one wants when you have milliseconds to burn a massive amount of fuel, as is the case with these engines. The element packs a large amount of energy into each kilogram, which matters when drag is rising steeply with speed and an aircraft is fighting against rapidly rising temperatures.

In most hypersonic designs, cold fuel can even double as a coolant, ultimately pulling heat out of hot structures or engine walls before it ever even enters the combustor, ultimately improving overall survivability and enabling longer powered runs. But hydrogen itself is a packaging nightmare. The compound’s low density means that bulky tanks that perform cryogenic liquid hydrogen freezing or high-pressure storage, both of which add mass, complexity, and safety, are ultimately required.

A hypersonic aircraft’s fuel system must remain stable under consistent vibration, rapid acceleration, and intensely rising temperature gradients, all while maintaining precise flow control for the engine’s narrow overall operating window. As a result, the use of hydrogen does not eliminate hypersonic risk but rather reshuffles what is exposed to it. The price for the speed created by hypersonic hydrogen-powered engines is hardcore integration work, including tanks, insulation, valves, and improved plumbing. Leak detection also needs to be spot on, and contingency plans need to be well-prepared.

A Highly-Capable Testing Vehicle

The Hypersonix Launch Systems’ DART AE (which stands for Additive Engineering) is an uncrewed hypersonic demonstrator aircraft that is intended to serve as a high-cadence, lower-cost flight testing vehicle. Instead of being designed as an operational jet-powered aircraft, the model is built to generate real-world data for the manufacturer’s air-breathing hypersonic engines.

Further studies of inlet behavior, combustion stability, thermal load management, and aerodynamics will need to be performed. The aircraft’s propulsion centerpiece is the SPARTAN, a fixed-geometric scramjet that burns hydrogen while breathing oxygen from the atmosphere. Hypersonix also leans heavily on additive manufacturing for the vehicle’s structure, ultimately using high-temperature alloys in order to shorten build cycles and enable faster iterations on the model. Here are some specifications for the aircraft, according to Hypersonix:

The vehicle itself is relatively small, and it is not expected to have any kind of exceptional range. Nonetheless, a powered, hypersonic aircraft with brief ballistic dash capabilities is exceptional, and its modular payload bay is designed to let customers add different kinds of sensors, telemetry packages, or experimental hardware to the aircraft’s design.

A Difficult Development Process That Has Many Challenges To Overcome

The development process here will be driven by a basic scramjet constraint, primarily that the aircraft is incapable of starting from a standstill. In Hypersonix’s public description of DART AE testing, the scramjet itself needs a boost to roughly Mach 5 in order to self-ignite, after which the air-breathing engine can take over for hypersonic acceleration and data collection.

In order to get the process rolling in the United States, Hypersonix has partnered with Rocket Lab in order to fly the DART AE under the Defense Innovation Unit’s HyCAT effort using Rocket Lab’s HASTE suborbital platform from Mid-Atlantic Regional Spaceport at NASA’s Wallops Flight Facility. Following separation from the parent aircraft, the autonomous model will test non-ballistic trajectories, controlled burns, and stable control long enough in order to demonstrate a clear ability to gather the data the drone aims to collect. Here are some additional specifications, according to Hypersonix:

In parallel, Hypersonix has worked with Kratos Defense on booster integration concepts, including references to Zeus solid rocket motors, in order to keep multiple launch options open as missions continue to evolve. Development timelines have also been shaped by the less glamorous work, including permits, export controls, and overall coordination across the Federal Aviation Administration (FAA) and the National Aeronautics and Space Administration (NASA).

Would It Be Possible For The Aircraft To Ever Fly 12 Times The Speed Of Sound?

Let’s be clear here. We are highly unlikely to see this particular demonstrator aircraft actually fly at Mach 12. Nothing in the manufacturer’s current published specifications would lead us to believe that. They are fairly clear that the aircraft’s expected top speed will be Mach 7. However, the place where Mach 12 potential comes into this story is the SPARTAN engine.

Hypersonix says that SPARTAN needs speeds of roughly Mach 5 to operate and that the powerplant is capable of driving a vehicle at speeds of Mach 12. This is more an aspirational hope made by an engine manufacturer than it is a verified performance point for the actual airframe itself. In order to actually reach Mach 12 in an atmospheric, controlled flight, one would need a vehicle optimized exclusively for that purpose.

The NASA-built X-43A briefly reached Mach 9.6, demonstrating how hard sustained hypersonic speeds are. Therefore, this claim remains extremely aspirational.

What Is Our Bottom Line?

The Hypersonix DART AE is a Mach-7 single-use hypersonic demonstrator that is aimed at collecting flight data, and it could potentially serve as a building block in the hunt to create a Mach 12-capable hypersonic aircraft. The aircraft has a single hydrogen-fueled SPARTAN fixed-geometry scramjet.

Because these kinds of aircraft are incapable of operating from rest, DART AE must be rocketed to around Mach 5 before the engine can self-ignite. Thus, the breakthrough is a repeatable booster-to-scramjet test architecture that offers exceptional performance.

History ultimately supports this caution, with the NASA-built scramjet hitting Mach 9.6 only briefly. This underscores how hard sustained, controlled hypersonic propulsion remains. In order to truly approach Mach 12, one would likely need a new airframe and a higher-altitude profile.